Guide to R83 & R84 Concrete Base · Guide to R83 and R84 Concrete Base NR83 Ed 2 / Rev 0 3 Extra effort devoted to construction quality will have a large impact in reducing the need

Edition 2 / Revision 0 ROADS AND MARITIME SERVICES August 2012

ROADS AND MARITIME SERVICES (RMS)

SPECIFICATION GUIDE NR83

GUIDE TO QA SPECIFICATIONS R83 AND R84 CONCRETE BASE

REVISION REGISTER

Ed/Rev Number

Clause Number

Description of Revision Authorised

By Date

Ed 2/Rev 0 New Edition, updated to accord with changes to base specification R83 and R84. Guide reference number changed from “CR83” to “NR83”.

GM, IC 29.08.12

Edition 2 / Revision 0 ROADS AND MARITIME SERVICES August 2012


GUIDE TO QA SPECIFICATIONS R83 AND R84

CONCRETE BASE Copyright – Roads and Maritime Services

IC-QA-NR83

VERSION FOR: DATE:

Guide to R83 and R84 Concrete Base NR83

Ed 2 / Rev 0 i

CONTENTS

CLAUSE PAGE

FOREWORD ...............................................................................................................................................II RMS Copyright and Use of this Document ...................................................................................ii Base Specification..........................................................................................................................ii P.1 Introduction ....................................................................................................................1 P.2 Quality Standards in Pavement Construction.................................................................3 P.3 Nomenclature and Abbreviations .................................................................................10

1 GENERAL......................................................................................................................................12 1.1 Revisions ......................................................................................................................12 1.2 References ....................................................................................................................12

2 MATERIALS ..................................................................................................................................12 2.1 Aggregate – General.....................................................................................................12 2.2 Fine Aggregate .............................................................................................................13 2.3 Coarse Aggregate .........................................................................................................14 2.4 Cement and Fly Ash .....................................................................................................14 2.5 Admixtures ...................................................................................................................14 2.6 Curing Compound ........................................................................................................15

3 DESIGN.........................................................................................................................................15 3.3 Mix Particle Size Distribution ......................................................................................15 3.4 Binder Content..............................................................................................................16 3.5 Strength ........................................................................................................................16 3.6 Consistence...................................................................................................................19 3.7 Other Attributes ............................................................................................................19 3.8 Nominated Concrete Mixes ..........................................................................................20

4 PROCESS CONTROL ......................................................................................................................22 4.1 Placing Steel Reinforcement ........................................................................................22 4.2 Production and Transport of Concrete..........................................................................26 4.3 Paving Concrete............................................................................................................35 4.4 Concrete Paving Trial...................................................................................................56 4.5 Joints and Edges ...........................................................................................................57 4.6 Kerb and Gutter ............................................................................................................66 4.7 Special Slabs.................................................................................................................68

5 END PRODUCT CRITERIA .............................................................................................................70 5.1 Concrete Cracking ........................................................................................................70 5.2 Concrete Compaction ...................................................................................................73 5.3 Concrete Compressive Strength ...................................................................................80 5.4 Geometry and Thickness ..............................................................................................81 5.5 Surface Profile ..............................................................................................................83 5.6 Removal and Replacement of Concrete Base...............................................................87 5.7 Rectification of Finished Surface and Ride Quality .....................................................88

ANNEXURE R83/3 - REQUIREMENTS FOR TECHNICAL PROCEDURES.....................................................90

A2 MATERIALS ..................................................................................................................................90 A2.6 Curing Compound ........................................................................................................90

A3 DESIGN.........................................................................................................................................91

NR83 Guide to R83 and R84 Concrete Base

ii Ed 2 / Rev 0

A3.2 Survey at The Top of The Underlying Layer ...............................................................91 A3.3 Mix Particle Size Distribution ......................................................................................91

A4 PROCESS CONTROL ......................................................................................................................92 A4.1 Placing Steel Reinforcement.........................................................................................92 A4.2 Production and Transport of Concrete..........................................................................96 A4.3 Paving Concrete..........................................................................................................112 A4.5 Joints and Edges .........................................................................................................119

A5 END PRODUCT CRITERIA............................................................................................................121 A5.2 Concrete Compaction .................................................................................................121 A5.3 Concrete Compressive Strength..................................................................................124 A5.7 Rectification of Finished Surface and Ride Quality ...................................................126

ANNEXURE R83/8 – STEEL FIBRE REINFORCED CONCRETE ..................................................................127 A8.5 Texturing.....................................................................................................................128 A8.8 Conformity for Compaction........................................................................................128

ATTACHMENT A – REFERENCES...........................................................................................................129

ATTACHMENT B – CHECKLIST FOR LABORATORY TRIAL MIX ............................................................131

ATTACHMENT C – PAVING TRIAL CHECKLIST .....................................................................................139

LAST PAGE OF THIS DOCUMENT IS ........................................................................................................142

FOREWORD

RMS COPYRIGHT AND USE OF THIS DOCUMENT

Copyright in this document belongs to the Roads and Maritime Services.

The Guide is not a contract document. It has been prepared to provide readers with guidance on the use of the specification.

BASE SPECIFICATION

This document is based on RMS QA Specifications R83 Edition 2 Revision 8 and R84 Edition 2 Revision 8.

(RMS COPYRIGHT AND USE OF THIS DOCUMENT - Refer to the Foreword after the Table of Contents)

Ed 2 / Rev 0 1


GUIDE TO QA SPECIFICATIONS R83 AND R84 CONCRETE BASE

PREAMBLE

P.1 INTRODUCTION

P.1.1 Scope

This User Guide aims to present a background to the requirements in R83/R84 with examples and illustrations to complement specific clauses. It is intended as a guide only for the Principal’s staff and has no contractual status. The Guide serves to assist the Principal’s staff when examining the contractor’s submitted mix design, process control and inspection and testing documentation at the start of a project and monitoring their implementation.

Whilst it contains much in common with the R82 User Guide (for lean-mix concrete subbase), there are also many differences which reflect fundamental differences between the two layers (i.e. subbase and base).

The major emphasis of the specification is to achieve:

the required quality in the Works, and

an assurance of consistency at that quality level.

P.1.2 Quality

In the absence of evidence of a consistent process, testing becomes ad hoc and not representative of the product.

Uniformity is a fundamental requirement of all manufacturing and construction operations. Clause 7.5.3 of Specification Q6 states:

“The Principal has the right to reject a lot that is visually non-homogeneous and/or non-representative.”

The specification distinguishes between controls relating to:

the quality of materials as supplied to site; (as reflected in cylinder/beam properties);

and

the processes used to incorporate those materials into the Works. (as reflected by insitu test results such as core properties).

Regarding standards of workmanship in concrete construction, Dr Peter Miller [9] states:

"Technological understanding of concrete is elementary. Its control is an art form. The most brilliant design depends for its success on the skill of the craftsmen dealing with the wet concrete. .... Current knowledge .... is sufficient to .... avoid most of the faults we see.”



2 Ed 2 / Rev 0

Many of the problems experienced in concrete paving in the 1990s and early 2000s are repeats of those we saw during the 1980s and so it is true that we should be able to “avoid most of the faults we see”.

In relation to airport pavements, Rollings (18) states the following:

“.... a well-built but poorly-designed pavement is likely to outperform a poorly-built but well-designed pavement. .... our problems in the field .... usually are human errors where we misuse our design tools and fail to deal adequately with site conditions, materials or construction processes.”

Experience from NSW concrete road pavements would seem to endorse these comments.

The same principles seem to apply to other sectors of the construction and engineering industry. Comments made by Watts Humphrey [8] (a software design manager) are equally applicable to concrete paving.

“When you hear a symphony orchestra, that’s 50, 60, 100 musicians all trained and disciplined to work together – and they don’t hit bad notes.

The real challenge is to catch cub .... engineers as they are starting out, before they imbibe the culture that ‘we practise on stage’.

Surprisingly, it costs less to do quality work than poor quality work. It’s so terribly expensive to fix software ....” (and distressed pavements).

The three most common management performance measures are time, cost and quality.

Time

Cost

Quality

Fast completion Minimum cost

Quality construction Choose any two!

Oz Construction Pty Ltd

Source: Mather (2002) & Scott (1995) Reference [25]

Unfortunately, too often it seems that Quality issues are neglected merely because of the greater emphasis being given to Cost and Time issues (i.e. “Dollars” and “Deadlines”).

The major consequence of the mismanagement of quality is that pavements too often provide only a fraction of the life which they should (and could) provide.

Quality is art .... unrestrained quantity is vulgarity (1).

The benefits of high output (i.e. quantity) are widely recognised and rewarded, and so rarely need to be stated. Unfortunately, the benefits of quality receive much less attention, and the consequences of poor quality usually don’t become apparent until several years later, by which time they are rarely the responsibility of those who were involved in the initial construction.

This Guide documents some of the consequences of variable construction quality in an effort to improve the success in identifying and correcting the contributing factors.

1 Dame Margot Fonteyne



Ed 2 / Rev 0 3

Extra effort devoted to construction quality will have a large impact in reducing the need for premature restoration under traffic. In other words, the benefit-to-cost ratio of improved construction quality is very high.

Plate P.1 – Pavement restoration under traffic

P.2 QUALITY STANDARDS IN PAVEMENT CONSTRUCTION

Neglect of the fundamentals of good concrete practice has been the cause of much of the premature distress in pavements and structures throughout the world. Local demonstration of this is the observation that much of the premature slab replacement within NSW involves concrete whose insitu (core) strength is only 22 to 30 MPa at ages of 10 to 15 years. These low strengths invariably result from permutations of factors like poor concrete (at the point of supply) combined with the impact of poor construction practices (particularly under-compaction).

The positive side of this is that improvement in the fundamentals is readily achievable and is certain to yield very significant benefits.

However, it will often require concerted effort on the part of site supervisors to achieve such improvement. Work standards within the general construction industry are highly variable, and arguably deteriorating with time, partly under the pressure for increased outputs. Crews that are accustomed to mediocre work practices in, say, domestic and high-rise construction, are likely to resist attempts by RMS staff to achieve higher standards which might seem (to those crews) to be pedantic and unwarranted. This will obviously present substantial challenges to site supervisors.

Plate P.2 – Standards and performance demands



4 Ed 2 / Rev 0

However, there should be no doubting that high standards are justified in highway work. Concrete which might perform adequately for decades in frame structures could fail within five years in pavement slabs. This is largely related to the following issues:

(a) pavements perform in flexural fatigue, which is very sensitive to the concrete quality;

(b) the reinforcement which might be used in a pavement (CRCP or JRCP) does little to enhance the fatigue performance (2), and;

(c) the probing and intense nature of truck loading is such that every single batch of marginal concrete will be heavily tested and exposed within a short period of service.

By comparison, high-rise concrete frame structures are heavily reinforced and exhibit substantial load distribution. It is therefore possible to bury many loads of marginal concrete within such a structure with little apparent compromise to its performance for several decades.

The benefits of quality are readily apparent from European highway experience. In 1992, a delegation of American highway officials undertook a study tour of European highways [27]. They reported that “.... European pavements are better (than American) even though European trucks are heavier and traffic volumes higher than in the US”. One of their explanations for this was that:

“.... the European emphasis is on quality and effectiveness, rather than efficiency ....”.

The following is a brief discussion of selected key issues. Many of these issues are common to the R82 User Guide and so have not been repeated therein.

Further information can be found in the Concrete Pavement Manual [3].

P.2.1 Formwork

Ride quality will depend very much on the accuracy of formwork placement, and on the accuracy of screeding.

Forms are generally timber, steel or a composite of both. For high quality work, forms should be set to tolerances at least equal to those specified for the finished surface because the screeding process will dictate the surface profile, and finishing operations can do little to correct poorly controlled screeding. Formwork straight-edge tolerance should be better than 3 mm in 3 m.

P.2.2 Reinforcement

Reinforcement should be supported in place on bar chairs to which it is tied. Sufficient chairs should be used to prevent deflections or displacement of the reinforcement during placing and compaction of the concrete.

An important consideration for tiebars and stitch-bars is the bond strength (or pull-out strength) because it can have major implications for the level of stresses in the pavement and hence on the pavement life.

The Austroads thickness design method allows for two edge conditions, viz with~ or without shoulder. In this context, the term “shoulder” refers to the adjacent lane, be it a shoulder or a trafficked lane. The key issue is the degree to which the adjacent lane provides load support to the lane in question.

Load sharing is dependent on shear capacity at the joint. Shear capacity is provided by aggregate interlock (or corrugations) and this will only be effective whilst the faces are kept in close contact.

2 with the possible exception of steel-fibre reinforcement.



Ed 2 / Rev 0 5

Tiebars (and stitch-bars) are provided purely to act in tension to hold the faces together and they have little effective shear capacity.

If the tiebars are ineffective and the joint opens excessively, the pavement will be acting in a “no-shoulder” condition and hence will have substantially reduced flexural life. Further, the alkaline environment required to protect the tiebars against corrosion will be depleted if the joint width (at the bar level) exceeds about 0.5 mm.

The highest rate of tiebar pull-out failure occurs where bars have been pushed into the edge of a formed slab or kerb. In particular, the nature of extruded kerb mix (as distinct from slipformed paver mix) is such that tiebar bond is highly unreliable. For this reason, extruded kerb is not permitted where it will be required to provide edge support close to commercial vehicle wheelpaths.

P.2.3 Consistence (slump)

The measurement and control of slump is arguably the most contentious issue in concrete placement. The practice of “wetting up” the mix (retempering) to aid workability is one which is discouraged by most clients but one which nevertheless occurs on a regular basis throughout the construction industry.

Loss of workability (or stiffening) in concrete derives largely from three sources, viz absorption of water by the aggregates, hydration of the cement, and evaporation.

Hydration and absorption both begin as soon as the constituents are mixed. However, under normal conditions of temperature and cement type, the degree of hydration which occurs in the first 25–30 minutes will be minimal. In warmer weather, concrete loses workability more quickly because of the increased rates of both hydration and evaporation.

Theoretically, retempering is acceptable within the first 25 to 30 minutes after batching because any stiffening during that time is due largely to absorption and evaporation, and hence any water added within that period is effectively only water which should have been added during batching. For the same reason, this addition is unlikely to push the water/cement ratio higher than that of the trial batch (which uses aggregates in the saturated-surface-dry condition).

In contrast, water added after about 30 minutes will be replacing not only that lost in evaporation and absorption, but also (increasingly) that lost to hydration.

The effects of retempering are as follows:

Strength: the compressive strength of the concrete will be reduced in direct proportion to the amount of retempering water added.

Shrinkage: Shrinkage will increase significantly.

Durability: The curing time required to achieve discontinuous capillaries in concrete (and hence impermeability) increases enormously as the water/cement ratio increases (from about 28 days at a water/cement ratio of 0.5, to 6 months at a water/cement ratio of 0.6).

It is important that all supervisors understand the consequences of retempering. In most situations, it would be far preferable to increase slump with a superplasticiser rather than with water.

When preparing specifications, careful consideration should be given to the likely supply conditions. The provisions of the Specification (and AS 1379) should be tailored and supplemented to suit site-specific conditions.



6 Ed 2 / Rev 0

With SFRC, there is an increased temptation to retemper because of its apparent low workability. Prior to commencement of construction, this issue should be fully discussed with batchers and agitator drivers to ensure that they do not over-wet the mix based on their experience with plain concrete.

P.2.4 Mixing Uniformity

Uniformity is a difficult property to assess and it remains a contentious issue even amongst experienced personnel.

Consistent uniform production (both within and between batches) is most likely to be achieved by dedicated batch plants employing consistent batching procedures and proven mixing times but, even under these conditions, major problems sometimes occur.

For fixed-form paving, mixing and delivery will invariably be by agitators and hence the potential for problems is obviously higher. The most likely sources of problems include variable charging procedures and inadequate mixing time.

It is a good practice to thoroughly mix all agitator delivered concrete at high drum speed on arrival at site. The mixing time should be in accordance with the identification plate which is required (by Standard AS1379 and Specifications R83/R84) to be fixed to every agitator.

Additionally, if any new material is subsequently added (such as retempering water) the full mixing period must be repeated in order to restore uniformity. For typical agitators, this will require 3½ to 4 minutes of mixing, but random observations throughout the construction industry suggest that this is rarely provided.

With steel fibre reinforced concrete (SFRC), the sequence and method of charging the mixer is critical. Even under favourable conditions, fibre “balling” or “clumping” can periodically occur and so site staff must therefore add this to their surveillance list. Fibre balls must be removed before their incorporation into the slab, and if they occur regularly, the mixing process should be investigated.

P.2.5 Placement and Compaction

The placement of concrete in pavements demands the highest standards of technique and workmanship. The finished work must be well compacted and cured, and close surface tolerances will be required to achieve a satisfactory ride quality; all of this under sometimes harsh and variable weather conditions.

A fundamental rule is that placing, spreading and compacting must be kept as distinct and separate operations.

More commonly on construction sites, vibrators are used to simultaneously spread and compact the mix. This practice is harmful in two ways. Firstly, it promotes segregation (though this is unlikely in RMS’s well-graded mixes), and secondly, the vibrator insertion time will wrongly be considered as “vibration time”. In reality, effective vibration doesn’t commence until lateral movement of the mix ceases.

To achieve the required standards of compaction and surface tolerance it is necessary to use both internal and surface vibration. Non-vibrating screeding techniques are unable to achieve adequate compaction and have proven unacceptable in structural applications such as paving. The literature also suggests that their shearing action may encourage plastic shrinkage cracking. The continued use of non-vibrating screeds in general construction work should in no way be taken as an indication of their effectiveness.



Ed 2 / Rev 0 7

Similarly, vibrating screeds alone (without prior internal vibration) are unable to achieve compaction throughout the full depth of the slab. Advertising claims to the contrary should be treated with extreme caution.

Correct placement and compaction procedures are therefore as follows:

(a) place and spread the mix into its final position (with shovels), and then commence:

(b) internal vibration, then

(c) surface screeding and vibration (2 passes minimum).

The concrete should be spread by shovel before commencing vibration.

Pavements require both internal and surface vibration.

Plate P.3 – Good placing and compaction techniques

Internal vibration

Extensive experience shows that one 50–70 mm vibrator working continuously can fully compact about 10 m3 per hour. Hence, if concrete is being placed at the rate of 30 m3/hour, then 3 vibrators will be needed, and they must be working continuously.

Vibrators can be dragged (as they are under slipformers) or “poked” but, in both cases, the compactive effort must be thorough and systematic. The vibrator should be inserted or dragged at spacings of not more than about 350 mm.

If the vibrator is dragged through the concrete, its speed should not exceed 1.5 m/min. If the vibrator is poked its insertion time should not be less than 5 secs.

Segregation due to over-vibration is highly unlikely in well designed paving mixes (such as those complying with RMS specifications) and the international literature indicates that it is very rarely seen.

By comparison, under-compaction is a common problem and is the frequent cause of premature failure of concrete. This is explained by the fact that a 1% deficiency in density causes around 5 to 6% deficiency in strength. In other words, 2% of voids in a 35 MPa mix will reduce the strength to about 31 MPa and will reduce the design fatigue life from 40 years to about 15 years.

Surface vibration

The first pass of a vibrating screed is used to level the mix. The second pass is required to achieve final surface tolerances and to finish compaction of the concrete in the upper zones, including those areas disturbed by workers' boots. On both passes it is important that a small surcharge be maintained ahead of the screed because it is this surcharge which transmits much of the vibration into the slab.



8 Ed 2 / Rev 0

In SFRC, there should be no doubting that compaction is just as important as it is in plain concrete. In addition to the usual benefits of good compaction, SFRC requires full and consistent compaction to achieve high fibre bond strength. The ACI [26], for example, recommends that: “For fibre-reinforced concrete, internal vibrators must be used at a closer spacing and for a longer period of time to obtain satisfactory results.”

P.2.6 Finishing

Finishing and curing techniques must be of a very high standard in order to achieve the specified surface tolerances with a surface texture which is durable under the abrasive action of high speed traffic. The difficulty of achieving this will increase substantially with increased paving widths beyond about 4.5 m.

Durability is related to concrete strength which, in turn, is largely influenced by water/cement ratio and effectiveness of curing.

In this regard, the two most common abuses of concrete involve:

the use of over-wet mixes, and

wet slurrying of the surface

Both of these practices are intended to aid the finishing operation, but they also result in a surface mortar of high water/cement ratio and hence low strength.

Supervisors should also be alert to the common abuse of sprayed evaporation retarders (aliphatic alcohols) as finishing aids. Such compounds are typically diluted with water and hence their use must be closely controlled to ensure that they are not slurried into the surface. Advertising brochures which encourage their use as finishing aids should be treated with caution.

P.2.7 Surface Texture

The surface texture of a concrete highway pavement is critical in terms of its influence on skid resistance, ride quality and noise generation. The surface must not only meet the target properties when new, but those properties are required to be durable under long-term trafficking.

In order to meet these requirements, the quality of the surface concrete must be substantially better than that which is typically found in industrial and structural applications, and this means that placing and paving practices must be of a higher standard than those used in the general construction industry. In terms of durability (i.e. abrasion resistance), the critical issues are concrete strength, water/cement ratio and curing effectiveness.

P.2.8 Curing

Pavements are typically constructed under severe exposure conditions and therefore RMS specifications require the use of high quality curing compounds and a high standard of application. The timing of application can also be critical, particularly under conditions which are conducive to plastic shrinkage cracking. The Concrete Pavement Design Manual [3] contains a detailed discussion of this topic.

Good construction practice dictates that curing should commence as soon as the bleed water sheen leaves the surface.

Curing must be in place before significant drying occurs and must thereafter be maintained long enough to achieve the required strength and durability, and to minimise shrinkage. The importance of timely and effective curing cannot be overstated.



Ed 2 / Rev 0 9

In very cold weather, action must be taken to prevent freezing of the surface. Polythene sheeting alone (preferably black) can maintain the concrete temperature up to 7°C above the outside air temperature if it is fully weighted along all edges. In colder situations, hessian may need to be placed under the polythene sheeting to increase the insulating effect.

P.2.9 Jointing

Sawcutting of joints has the following advantages over formed joints:

concrete is placed monolithically, resulting in better surface finish and ride quality;

sawn joints are always perpendicular to the surface, resulting in no weakened edges or corners;

because there is no handwork in the joint area, concrete around the joint has the same properties as the rest of the pavement;

edge slump at the joint is avoided.

The main difficulty in sawcutting is determining its optimum timing. This can vary significantly depending on the temperature, humidity, aggregate type and other factors which affect the hardening and shrinkage rates.

It will only rarely be possible to postpone sawing until the morning after placement, and this applies equally to transverse and longitudinal sawing.

In summer, cutting may be required as soon as 4 hours after placement but in winter this could rise to 18 hours or more.

Premature sawing will result in excessive spalling at arrisses, whilst late sawing will result in unplanned random cracking.

A compromise is therefore required, and it is generally accepted that a small amount of ravelling is expected. The production of perfectly sharp and square edges indicates that sawing was probably a little late, with the attendant risks of random cracking. SFRC will probably ravel slightly more than plain concrete because of the plucking of fibres.

Typically, a single sawblade width is cut initially and this is later widened prior to sealing. The widening cut will generally remove most of the ravelling caused by the first sawcut.

Sealing must include the vertical face at each formed edge.

At all formed joints, the first-placed face must be positively treated to ensure debonding from subsequent pours.

P.2.10 Testing

A clear distinction needs to be understood between cylinder properties and insitu properties (as reflected by cores).



10 Ed 2 / Rev 0

Plate P.4 – Core versus cylinder properties [12]

P.3 NOMENCLATURE AND ABBREVIATIONS

Nomenclature

abcd [1] Referencing numbers for endnotes (listed under Appendix A “References” at the back of this Guide) are shown enclosed within square brackets [] in superscript.

wxyz (2) Referencing numbers for footnotes (shown at bottom of same page) are shown enclosed within round brackets () in superscript.

Extract… Statements shown with shading are extract of clauses from Specifications R83/R84.

Sections The term “Section” is used in this Guide to avoid confusion with “Clauses” in Specifications R83/R84. Hence, Section xyz in this Guide relates to Clause xyz in R83/84.

Section numbers which are prefixed with “A” relate to Annexures.

Plates Figures and Tables in this Guide have been referred to as “Plates” in order to avoid confusion with similar items in Specifications R83/R84.

R83/R84 For simplicity, “R84” is subsumed in “R83” for the remainder of this Guide.

Base An uppercase “B” is frequently used for “the Base layer” in any context where ambiguity seems possible.

Abbreviations

SMZ Selected material zone

LCS Lean-mix concrete subbase



Ed 2 / Rev 0 11

PCP Plain concrete pavement (base)

PCP-R Discrete mesh reinforced slabs within PCP

CRCP Continuously reinforced concrete pavement (base)

JRCP Jointed reinforced concrete pavement (base) - dowelled

SFCP Steel fibre reinforced concrete pavement (base)

SFRC Steel fibre reinforced concrete

CSIRO Commonwealth Scientific and Industrial Research Organisation, Australia

NATA National Association of Testing Authorities, Australia

RMS Roads and Maritime Services

AAR Alkali aggregate reactivity

FA Fly ash



12 Ed 2 / Rev 0

1 GENERAL

1.1 REVISIONS

For practical and logistical reasons, this Guide is revised when warranted and independent of revisions to the Specifications which it supports. Hence, there may be differences between the specification clauses which are quoted in this Guide and those which appear in current contracts.

Users therefore need to assess whether the advice contained in this Guide is relevant to their specific application.

1.2 REFERENCES

In some cases, standards have been referenced even though they may have been withdrawn. An example is AS 1141.61 (1974) which was withdrawn in 1998. This is generally only done where no acceptable alternative exists.

2 MATERIALS

2.1 AGGREGATE – GENERAL

During the contract, all aggregate testing must be on samples taken either from dedicated stockpiles or from materials delivered to site.

“Dedicated stockpiles” need not be at the construction site but may be in a designated area of the quarry. It makes no sense to transport untested, marginal or nonconforming materials.

.... all aggregate must be assessed for potential alkali-aggregate reaction ....

The petrographic examination is not a substitute for T363 or T364 but is intended to screen out those aggregates which can be readily identified (by a petrographer) as reactive. It is not intended to measure whether an aggregate is non-reactive or otherwise, but is intended to quickly eliminate from contention those aggregates proven in the past to be reactive because of their mineral composition and/or history.

The CSIRO 21 day accelerated mortar bar test (T363) is not always conclusive, due to inaccuracies in the measurements and variations between laboratories, and the results are not reliable when blended cements are used.

A recognised Australian guideline for AAR is the joint publication by Standards Australia and the Cement and Concrete Association titled “Alkali Aggregate Reaction - Guidelines on Minimising the Risk of Damage to Concrete Structures in Australia”, 1996.

Based on available literature, the guidelines recommend minimum proportions of SCMs (3) (e.g. minimum fly ash content is recommended to be 25%). The guidelines give scope for other SCM proportions provided their effectiveness is evaluated, and they indicate that the best method for evaluation is the concrete prism test (T364). However, this test can take up to two years and so will often not be practical or viable.

3 SCM: supplementary cementitious materials



Ed 2 / Rev 0 13

As stated, there are uncertainties in using the accelerated mortar bar test (T363) for evaluation of effectiveness of SCMs in suppressing reactivity (4). Neither the American standard ASTM C1260 nor the Canadian standard CSA A23.2-25A (both are similar versions of the accelerated mortar bar test used in Australia) suggests their use for the evaluation of SCMs.

2.2 FINE AGGREGATE

Sand quantity and quality largely dictates the level of skid resistance and its durability.

The chert/quartz ratio was introduced to control certain sands (such as conglomerate sands) which have a high content of aggregated fine sand cemented by clay. These particles have poor durability and are likely to break down, both during handling/batching and within the surface under traffic.

The specification allows the use of a proportion of manufactured fine aggregate. Sources that have been successfully used in concrete road projects are:

crushed sandstone;

“crusher dust” from a hard rock quarry (without deleterious minerals);

granulated blast furnace slag.

Workability of the mix is a key issue in relatively low slump concrete such as slipform mixes which are typically around 35 mm slump. The same applies (albeit to a lesser extent) to hand-paved and normal concretes with slumps within the range 60 – 80 mm.

Slivered and elongated fine aggregates adversely affect workability and have a higher surface area per mass, which increases the water demand. For this reason, tertiary crushing is recommended to achieve cubical shape. Washing of hard rock manufactured sand is also recommended in order to minimise the dust content.

.... natural sand to have at least 70% (by mass) quartz and chert particles ....

As discussed in the Background Notes within Section 5.5.2, the important surface texture profiles are:

microtexture (desirable);

macrotexture (desirable);

megatexture (undesirable), and;

roughness (undesirable).

Microtexture is largely provided by the sand fraction within the mortar, and macrotexture is provided by treatments such as tining. The majority of the surface friction is provided by the microtexture (i.e. the sand content), and the main function of the macrotexture is to remove surface water under the tyre (at high speed) in order to maximise tyre contact with the microtexture (i.e. to avoid aquaplaning).

The specification requirement for a high quartz content is intended to maximise the durability of the microtexture.

4 Hooton D, 10th International Conference on AAR in Concrete. Melbourne (Aust) 1996.



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2.3 COARSE AGGREGATE

The maximum aggregate size adopted in the specification is 20 mm. This limit on aggregate size is placed to ensure that segregation of the mix is limited. The use of larger aggregate also adds complications with test specimen sizes, particularly for flexure beams.

The Average Least Dimension (ALD) requirements in AS 1141.14 have been supplemented in order to control aggregate shape on the portion passing 9.5 mm. This has a significant impact on workability and is thought to have contributed to differential plastic settlement around reinforcement.

2.4 CEMENT AND FLY ASH

Currently Portland cement and fly ash are defined as cementitious materials or binders permitted by the specification (refer to Clause 2.4 and 3.4). Fly ash improves workability, reduces the heat of hydration, reduces the potential for the onset of AAR and enhances long-term strength development.

Shrinkage Limited (SL) cement helps to limit the magnitude of joint openings.

Fly ash criteria such as loss on ignition (LOI), moisture content and SO3 content seek to ensure that the fly ash provides sufficient pozzolanic action with little detrimental effect on the hardened concrete.

In addition to the actual value of fly ash properties (such as LOI), it is also important that variability be controlled because significant fluctuations are likely to cause substantial variability in the concrete properties. To this end, fly ash should be monitored for consistency, such as possible fluctuations between Fine and Medium grades.

Fly ash, being generally spherical in shape, improves the workability of a mix, but its hydrophobic nature increases the required mixing time; see Section 4.2.2.

2.5 ADMIXTURES

When used under controlled conditions, admixtures provide very worthwhile benefits in paving. For example, it is far preferable to control slump loss using set retarders rather than by retempering the mix (refer to Section A4.2.2(f)).

Air entrainment improves slipformability and controls bleeding.

Ingredients such as calcium chloride, calcium formate, triethanolamine or other accelerator are discouraged because of concerns over properties such as shrinkage (particularly if over-dosed), and corrosion potential on reinforcement such as tiebars.

For combinations of two or more admixtures, their compatibility must be certified in writing by the manufacturers.

This requires consideration of two issues:

(a) If the admixtures are allowed to intermix in their concentrated form (or only partially diluted), is an adverse interaction likely? Some combinations, for example, form an insoluble gel if they intermix in the concentrated form.

(b) Assuming that incorporation into the mix is completed in accordance with the manufacturer’s guidelines, is an adverse interaction likely?

See Section 4.2.2 for further discussion.



Ed 2 / Rev 0 15

2.6 CURING COMPOUND

Surfacings such as asphalt and linemarking will not bond well to many types of curing compound. In some cases, positive removal of residual compounds may be necessary.

C5 compounds will typically degrade within 1-2 months under ultraviolet light but C9 compounds may last many months.

It is desirable to limit the maximum early temperature of the Base in summer in order to:

(a) minimise thermal shock on the first night, and

(b) limit residual concave curling, and

(c) limit joint openings in subsequent winters.

Reflecting compounds will reduce the solar component of the maximum temperature during peak hydration.

For cold-weather paving, reflecting compounds are undesirable because they would:

(d) inhibit early strength gain, hence delay sawcutting, and

(e) increase convex curling in subsequent summers, a condition which creates high slab stresses under truck loading.

The specification requires testing during the project to ensure that the product being supplied is consistent with that which was proposed (and which was presumably supported by conforming test data). There have been several notable cases where audit testing has identified nonconforming product being used on major projects.

A 3-stage testing program is used with the intent of maximising the chances of identifying nonconforming product whilst moderating the amount and cost of testing. See Section A2.6.

Note that aliphatic alcohol (commonly used to minimise moisture loss during the plastic phase) is not a curing compound.

3 DESIGN

3.3 MIX PARTICLE SIZE DISTRIBUTION

At least 38% by mass of the total aggregates in the concrete mix must be fine aggregate. The particle size distribution of combined aggregates must comply with Table R83.5 ....

The combined grading curves are based on work carried out by the TRRL(5) and published in their Road Note 4. The curves are still widely used in Europe. With few exceptions, they provide a mix with good workability and high resistance to segregation.

The 38% requirement (an RMS addition) is intended to ensure adequate microtexture for friction purposes (i.e. a sandpaper surface).

Wet-sieving is not mandatory but it should be carried out occasionally as a surveillance and audit process to assess mixer efficiency.

5 Transport & Road Research Laboratory, Dept of Transport, UK.



16 Ed 2 / Rev 0

3.4 BINDER CONTENT

Minimum cementitious contents are specified to ensure the achievement of adequate strength in the Works in contrast to “in the cylinders”, particularly under colder temperature conditions.

The distinction is important because the pavement is typically cured under very different conditions to the test cylinders and beams. Whereas the specimens are cured under saturated conditions at 23 2C, the pavement is cured with a sprayed compound (typically with 90-95% efficiency) and at fluctuating temperatures. Hence, there is no assured correlation between the strength of the specimens and the slab.

For this reason, RMS requires a safety margin on cementitious content.

In the case of SFCP, higher cement contents (and hence higher strengths) are required in order to ensure the high fibre pull-out strengths which are needed for toughness. See also Section A8.

3.5 STRENGTH

(a) Specimens

Both flexural and compressive strengths are important in pavement construction. Flexural strength is the basis for pavement design models, whilst compressive strength is important for its correlation with resistance to surface abrasion.

The specification uses compressive strength for acceptance/rejection because:

(i) compression cylinders are robust and less susceptible to moulding variability, and;

(ii) cylinders allow a degree of correlation with cores in the event of a dispute.

Flexural strength is required to be monitored in order to provide correspondence with the design assumptions and also because it is more sensitive than compression testing to materials changes (such as dust coatings on aggregates).

(b) Design versus contract strength

It is important to note the difference between the design flexural strength and the specified minimum strength under the contract. The typical design strength is 4.25 MPa whereas the specification requires a minimum strength of 4.5 MPa, a difference of about 10% (6).

The reason for this is that the Austroads design model is based on 90-day strength and assumes a gain of about 10% between 28 and 90 days (7). Hence, it is assumed that a 28-day strength of 4.25 MPa will increase to 4.5 MPa at 90 days. However, there is strong evidence that fine-grind Australian cements will only increase by about 3% under field-cured conditions. Hence, if a 90-day strength of 4.5 MPa is required then it is necessary to achieve this strength at 28 days.

For Client Project Managers, the relevant issue is that the thickness design must be based on a strength 10% below the specified minimum contract value which in all but rare cases will be 4.5 MPa, hence the design value will typically be 4.25 MPa (8).

6 ~except that SFCP is designed for 5.5 MPa. 7 1991 Edition; future versions may vary in this regard. 8 This anomaly will be removed in the current review of the Austroads Guide, hopefully by 2003.



Ed 2 / Rev 0 17

However, the design of steel fibre concrete pavement (SFCP) is an exception to this rule in that the 10% factor is not currently applied. In other words, both the design strength and the specified minimum contract strength are typically 5.5 MPa.

Plate 3.1 Results of German work [6] on age-strength development

The above discussion is consistent with a study carried out in Germany (see Plate 3.1) which showed that the 3.8 MPa concretes used during the 1930s with very coarse grind cements actually achieved a flexural strength of around 5.5 MPa by the time significant traffic loads were imposed. For equivalent design conditions under today’s traffic, 28-day flexural strengths of 5.5 to 7.0 MPa would theoretically be required. European specifications typically require about 5.5 MPa.

(c) CRCP strength limits

Until recently, upper limits were imposed on concrete strength in CRCP because the intent of the steel design is to achieve a balance between the tensile strengths of the concrete and the steel, in order to induce a desirable spacing of transverse cracking. Higher concrete strengths will theoretically result in cracking with increased spacings and widths (9).

However, longer-term experience indicates that higher strengths have relatively little adverse influence (if any) on cracking patterns and on pavement performance. Recent American surveys seem to confirm this [24]. Consequently, the upper limit has now been removed.

At the lower end, experience has shown very clearly that CRCP is sensitive to low strengths, particularly where that low strength is related to poor compaction (10); see further discussion in Section 5.2

(d) Moulding of specimens

Clause 3.5 contains requirements from both AS 1012.8 and RMS T304.

Details such as specimen sizes are required to comply with AS 1012.8 (11). However, it is important that moulding be in accordance with T304. Specimens which are moulded in accordance with AS1012.8 are nonconforming under Specification R83 and so all test certificates must be closely examined for this detail; refer to the Trial Mix Checklist in Attachment B.

9 The RMS’s use of this upper limit appears to have been unique in the World and it received endorsement in

a TRRL state-of-art report on CRCP design [23]. 10 One of CRC’s classic distress modes, block failure or “punch-outs”, appears to be closely correlated with

low strength concrete. CRCP appears to be even more sensitive than jointed pavements to low strengths. See further discussion in reference [17].

11 ~ because there is no reason to vary these details, and duplication in T304 is unnecessary.



18 Ed 2 / Rev 0

Under AS1012.8, various methods of compaction are allowed. If rodding is used, the number of strokes is precisely specified whereas, in the case of vibration, parameters such as the vibration time are left to the discretion of the operator. Not surprisingly, therefore, RMS laboratory trials have shown that the test method gives inadequate assurance of repeatability, particularly for the lower slumps that are required for paving work.

Plate 3.2 Test Method T304 provides specific guidelines for the moulding of specimens.

Test Method T304 requires:

(i) that internal vibration be used (12), and the durations are specified, and

(ii) that the vibrator be electric-powered, to ensure reasonable consistency both within and between projects.

Under R83, the cylinder unit mass is used as the reference value for assessment of slab compaction (12). Given that vibration is always used in the Works (i.e. never rodding), it would be illogical to allow rodding of the specimens.

The subject of compaction (and T304) is discussed in greater detail in Sections 5.2 and A5.2.

In the case of SFRC, restrictions are placed on internal vibration and rodding because of the risk of unfavourably realigning the fibres.

Plate 3.3 shows two cylinders (of unknown sources) selected at random from the disposal area behind a testing laboratory. The difference in compaction is obvious (13). Test Method T304 seeks to minimise such variability.

12 The exception is steel fibre reinforced concrete; see R83 and T304 for details. 13 Given the variability of specimen compaction in the general construction industry, it is not inconceivable

that concrete could periodically be (wrongly) deemed nonconforming simply because of poorly moulded cylinders. In other words, a good batch of concrete can fail on compressive strength if the cylinders are inadequately compacted. The rodding of concrete with slumps within the range, say, of 40 to 60 mm invites such a risk.



Ed 2 / Rev 0 19

For consistency, vibration is used in both the Works and in the specimens.

Two cylinder specimens of very different compaction standard.

Plate 3.3 – Specimen compaction

3.6 CONSISTENCE

For slipform concrete mixes, the Vebe reading must not exceed 3 seconds in the trial mix ..

Vebe is a very good indicator of the likely slipformability of the mix in the field.

See Section A8.3.3 for discussion of slump for SFRC.

3.7 OTHER ATTRIBUTES

Attribute Test Method Requirement

Bleeding AS 1012.6, with compaction by internal vibration

3% maximum

Air content of fresh concrete

AS 1012.4 Method 2, with compaction by internal vibration

4.5 1.5 %

Significant nuisance bleeding in the Works can be an indication of deficiencies in the 300m and 600m gradings.

Entrained air improves slipformability and reduces nuisance bleeding.

Entrained air will theoretically reduce the strength of the concrete in the same way as entrapped air does. However, entrained air improves the workability to the extent that the water/cement ratio can typically be reduced, and this reduction largely compensates for the strength loss.

AEA should never be used unless it will be regularly monitored and tested. As an example of the potential risks, projects are known within NSW where air content was not checked during the early stages of the work and, when testing was eventually commenced, it was found to be around 15%. The effect was to reduce a 35 MPa mix to about 20 MPa.

Variations in the carbon content of fly ash can also cause significant fluctuations in air content, which is a further reason to closely monitor the air content.



20 Ed 2 / Rev 0

AEA is not permitted in SFRC because of its adverse influence on fibre bond strength.

3.8 NOMINATED CONCRETE MIXES

3.8.1 Submission of Nominated Mixes

Plate 3.4 – Laboratory trial mixing

The trial mix is an important element in the specification. It should be used by the contractor to evaluate properties such as compactability, workability, slipformability and bleed potential.

The key requirements for the trial mix submission are:

(a) to certify that each nominated mix and its constituents meet the requirements of the Specification,

(b) to submit NATA endorsed test results, and

(c) to submit a verification checklist to show that all requirements have been checked and that they comply.

Note that the certification of conformity must be by the contractor; it cannot be accepted from a subcontractor (with whom RMS has no contract).

Cases have been encountered in the past where mix submissions which had been prepared by the concrete supplier(14) were forwarded to the Principal via the paving subcontractor and the prime contractor, apparently with only cursory checking by those parties, whereafter significant nonconformities were identified by the Principal’s staff. The resulting delays are an unnecessary inconvenience to all parties.

It is important that the supporting test results show that all specimens were prepared specifically in accordance with Specification R83. For example, test specimens which are moulded in accordance with AS1012 (rather than T304) are nonconforming; see discussion under Item 3.5.

Additionally, in the case of specimen compaction, R83 requires that the type of vibration be stated on the certificate. For example, electric internal (EI) vibration is mandatory for PCP cylinders (15).

14 There is no reason why the submission can’t be prepared by the supplier, but it must be checked and

certified by the Contractor. 15 Other types are external vibration (EV, such as vibrating tables) and Tee-bar (TB, for SFRC only).



Ed 2 / Rev 0 21

A trial mix checklist is attached to this Guide as Attachment B. The checklist is intended for use by both contractor and client staff and was prepared in response to the frequent omissions and errors found in past submissions.

Given the relatively low cost of trial mixes and the substantial ongoing consequences of their results, several trials would seem the minimum realistic requirement in order to be able to assess the sensitivity of the proposed mix to variations in its constituents.

Specific instructions should be given to the laboratory regarding issues such as the sequence of addition of ingredients.

In the case of admixtures, for example, the sequence and method of incorporation can have a significant impact on their behaviour and so the trial mix should simulate the procedures which the contractor proposes to use in the Works. As an example, if the contractor proposes to pre-dilute the admixtures in the mixing water then this should be simulated as far as possible in the trial rather than adding them to the pan in the concentrated form.

Witness Point

The Witness Point has been included in order to ensure that the Principal’s staff is given the opportunity to observe the trial mix.

…. indirect tensile strength at age twenty eight days (Ft28);

Indirect tensile (IT) testing has been included for the following reason.

Where doubt exists about cylinder results, cores can be taken for analysis. The same cannot be done in the event of a problem with beam results because there is no accepted procedure for the flexural testing of a beam taken from a slab. However, a compromise solution would be to take cores for IT testing. In any such analysis, it would be valuable to have a flexural/IT correlation from the trial mix.

Hence, the relationships shown in Plate 3.5 would be available for analysis.

Plate 3.5 – Test correlations

Cylinder UCS

<------------>

Flexural <------------>

Cylinder IT

Tri

al M

ix

Cylinder UCS

<--------------

-----------------------------

> Cylinder

IT

Flexural <--------------

----------------

-------------->

Core IT

Fie

ld

Cylinder UCS

<------------>

Flexural Cylinder

IT <------------

> Core IT

Compressive strength at .... seven days (F7) .... and twenty eight days (F28)



22 Ed 2 / Rev 0

The contractor is required to monitor the 7-day field results as an indicator of likely 28-day results. The trial mix ratio of F28 to F7 is useful for possible later comparison with field results, particularly if the field 7-day results are marginal; see Section A4.2.1.

Flexural strength at age seven days (Ff7) .... and .... twenty eight days (Ff28)....

The ratio of Ff28 to Ff7 is useful for the same reason; see Section A4.2.1.

Similarly, the correlation between compressive and flexural strengths should be calculated. The relationship is typically as follows:

Ff = k (Fc)½

The constant “k” should be calculated for the trial mix, for subsequent comparison with field results.

The value for “k” will vary between different mixes but will generally fall within the range from 0.68 to 0.82 (for typical pavement mixes).

However, for a specific mix produced under controlled conditions, the value should be reasonably stable and so it is valid to expect consistency between the value derived from the trial mix and the value in the field, with the following provisos:

(i) for field results, “k” should be calculated on the basis of mean results from a representative sample of data. Given the small number of flexural beams which are cast each day, weekly averages will be more relevant.

(ii) It is assumed that compressive and flexural specimens are “moulded from the same homogeneous batch”, as required under Specification R83.

(iii) The trial mix provides only a single data set which could fall anywhere within the normal distribution. In practice, however, laboratory trial mixes can be expected to yield a lower standard deviation than field production.

The unit mass must be reported for all specimens tested under items ....

If moulding has been in accordance with Test Method T304, the unit mass of all cylinders should be consistent, typically within a range not greater than 20 kg/m3.

The unit mass of beams should be similarly consistent (within the five results) but the actual values are sometimes 10 or 20 kg/m3 lower than the cylinders.

4 PROCESS CONTROL

4.1 PLACING STEEL REINFORCEMENT

4.1.2 Tiebars

.... no disturbance to the finished concrete surface ....

Defects can occur above tiebars that have been depressed through the surface during slipforming. The depression left in the surface will commonly be filled by mortar (sometimes from an oscillating screed) and this soft zone will be susceptible to deeper tining than the surrounding surface.



Ed 2 / Rev 0 23

Surface depressions over tiebars are also an indicator of possible underlying defects. Far more serious than a surface depression is the presence of a voided slot above the tiebar. This is a result of inadequate recompaction of the void which has been created by inserting the tiebar. It represents a classic crack initiator and is very likely to result in premature fatigue cracking. See further discussion under Section A4.1.2.

.... full reinstatement of the structural integrity of the affected slab ....

See Section A4.1.2 for discussion.

.... vibration of all tiebars in their final position ....

Tiebars have a major influence on the structural life of the pavement (see Section A4.1.2) and so it is critical that they achieve full pull-out strength. This could be doubtful if they are inserted into the side of the slab without subsequent vibration of the surrounding concrete. See Section A4.1.2 for discussion.

Testing must be conducted for tiebar location .... in accordance with Annexure R83/3.

Erratic (nonconforming) tiebar placement has been a recurring issue throughout the slipforming era. The required periodic location testing should be strictly followed, particularly during the early stages of the contract.

.... tiebars must be placed not closer than 300 mm to a transverse untied joint ....

Tiebars which cross a moving joint (such as contraction and isolation joints) will invariably generate cracking and subsequent spalling within the joint. This will be initiated (as microcracking) within a few days of paving and will widen later when the joints open further. Plate 4.1.2 shows a core which was taken through a tiebar where it crossed a transverse contraction joint. Damage to the slab is evident. A disposition which merely proposes sawcutting of the tiebar is unacceptable because the damage has already been initiated by the time the sawing can be undertaken.

Plate 4.1.1 Required clearance between tiebars and contraction joints.

Plate 4.1.2 Damage caused by a tiebar (in a longitudinal joint) which crossed a contraction joint

Plate 4.1 – Tiebar separation from contraction joints



24 Ed 2 / Rev 0

An upper limit of about 600 mm separation is desirable (between transverse joints and the nearest tiebar) to maintain close contact of the longitudinal joint faces, thereby ensuring adequate load transfer in the slab corner.

.... tiebars must be placed .... to ensure a minimum vertical clearance of 30 mm to any crack inducer (or sawcut).

This is intended to minimise the potential for corrosion.

In the case of CRCP which is paved over dual-lane widths, it is important that the steel be placed and surveyed accurately in order to avoid conflict with the longitudinal sawn joint. Plate 4.2 shows two examples where conflict of this type is likely to have occurred, as follows:

Plate 4.2.1: There is reasonable doubt that this meandering gap would be accurately marked out on the fresh concrete for the sawcutter's guidance. Even if it were, and given that sawcutting invariably takes place at night, it is unlikely that the sawcut would have faithfully followed the intended line.

Plate 4.2.2: No provision has been made for the required longitudinal sawcut.

In both cases, it is almost certain that the required minimum clearance between the sawcut and the steel would have been significantly compromised. This is likely to lead to premature corrosion of the transverse steel/tiebars. Plate A4.3 shows that failure of tiebars can reduce the pavement fatigue life to 25% of its design life.



Ed 2 / Rev 0 25

Plate 4.2.1 A (meandering) gap intended to cater for the longitudinal sawcut.

Plate 4.2.2 A longitudinal sawcut will be required in the centre of this pour but no provision has been made in the steel.

Plate 4.2.3 – Steel congestion Steel placement such as this (at a transverse CRCP joint) hinders the insertion of vibrators and so encourages under-compaction and premature failure.

Plate 4.2 – Reinforcement at joints

4.1.3 Dowels

Whereas tiebars are intended to prevent joint opening, dowels are located within joints that are designed to open. Furthermore, the first movements will invariably occur within a day of construction whilst the concrete still has a very low tensile strength. Hence, any impediment to joint movement is likely to generate unplanned cracking.

Impediments include misalignment of dowels and inadequate debonding.

Care is also required to ensure that the dowel support cage does not impede joint opening. To this end, there must be no steel crossing the joint except for the dowel. Hence, for example, the cross-wire shown in Plate 4.3.1 is intended purely to assist during placement of the cage, and must be cut prior to paving.

Similarly, it is important that the method used to fix the cages to the subbase does not create undue impedance to slab movements within the critical early days after paving. Where dowels are attached



26 Ed 2 / Rev 0

to reinforcing mesh (see Plate 4.3.2), provision must be made to allow movement at one end of the dowel relative to the mesh. Where only one end of the dowel is debonded, this movement will need to occur at that end.

Test Method T366 (for dowel debonding) is based on the UK Department of Transport test [11].

Plate 4.3.1 (above) A dowel assembly as typically used in the USA (where they are commonly referred to as dowel “baskets”). This arrangement can be used in plain (unreinforced) pavements.

Plate 4.3.2 (right) Dowels fixed to reinforcing mesh.

Plate 4.3 – Dowel installation

4.2 PRODUCTION AND TRANSPORT OF CONCRETE

4.2.2 Mixing, Transport, Consistence and Air Content

Good concrete is made from:

good cement

good aggregates, and

good water

Bad concrete is made from exactly the same!

The specification requires several properties of the fresh concrete to be tested and monitored to ensure that the mix is uniform both within and between batches.

The handling, storing and batching of materials and the mixing, transport and consistence of concrete .... must comply with AS 1379 (Section 4 and Appendix A) ....

Note that only specified clauses from AS 1379 are called up, and not the whole document.



Ed 2 / Rev 0 27

Mixing time

The minimum mixing time must be determined from mixer uniformity testing..

Uniformity is a difficult property to assess, and it remains a contentious issue even amongst experienced personnel. The most likely sources of problems include poor charging procedures and inadequate mixing times.

Fly ash mixes may require longer mixing times (than non-FA mixes) because, as a result of its hydrophobic nature, fly ash requires adequate time to become fully wetted, i.e. “conditioned”. Failure to provide adequate conditioning time can result in subsequent absorption and slump loss. This will increase the susceptibility of the paved mix to plastic shrinkage cracking.

If drying occurs within a tipper truck (i.e. non-agitating truck), nothing can be done to restore workability. If it occurs within an agitator, re-mixing may be successful in restoring workability (at least partially, even without further water addition), particularly if the mix contains an air entrainer (16).

Consistent uniform production (both within and between batches) is most likely to be achieved by dedicated batch plants employing consistent batching procedures and proven mixing times but, even under these conditions, major problems periodically occur.

Where mixing and delivery is in agitators, the potential for nonconformity is higher. Evidence of this can be seen by selecting a civil construction site at random to monitor the remixing procedures after the addition of admixtures (such as superplasticisers) and/or retempering water. A comparison of the specified minimum mixing times (as marked on each truck’s identification plate) with the actual times will often reveal alarming discrepancies.

It is a good practice on any project to thoroughly mix all agitator-delivered concrete upon arrival at site, and this is mandatory under RMS paving specifications. The mixing time must be in accordance with the identification plate which is required (by Standard AS1379 and R83) to be attached to every agitator. As an acceptable alternative, some companies have a system whereby the NATA certificate is kept in the truck. Further discussion is provided in Section A4.2.2.

Special care is required in the mixing of steel-fibre reinforced mixes to ensure thorough distribution of the fibres. Further discussion is contained in Section A8.3.7.

For mobile batch mixers, the full period of mixing must be provided at either the testing station or the point of placement.

This requirement has been introduced in response to recurring problems associated with inadequate mixing; see Section A4.2.2 for a more detailed discussion.

Admixture addition

Admixtures must be separately and thoroughly prediluted in the mixing water prior to their introduction to the other materials .... and by a method which ensures that no adverse interaction occurs.

As stated in Section 2.5, there is a risk of adverse reactions with some combinations of admixtures. This appears more likely to occur where the materials are allowed to intermix prior to full dilution.

16 Remixing of entrained mixes can rejuvenate the AEA, which is likely to partially restore slump and

workability.



28 Ed 2 / Rev 0

This has been the cause of major problems on at least two RMS projects. Plate 4.4 shows the removal of several kilometres of base concrete which exhibited extreme variability largely as a result of admixture interaction. Cores removed at 0.3 m centres across a specific chainage yielded compressive strengths ranging from 8.0 MPa to 45.0 MPa. Mixing times on this project were also substantially shorter than those typically required to achieve mixer uniformity.

Cores from the pavement exhibited distinctly non-uniform drying after saturation. The “wet” areas were those where admixture dosage and air content were highest.

The fractured slabs showed clear “marble-cake” composition. Note the horizontal lens of mortar (outlined).

Plate 4.4 – Non-uniformity related to admixture interaction

Subsequent enquiries revealed that the contractor had been using AEA(17) dosage rates 400 to 500% higher than recommended levels in order to try to achieve the specified air content. The elevated dosages had little effect in raising air content because it was being neutralised by interaction with the WRA (17) in the water supply line.

Clearly, atypical fluctuations in admixture dose rates or atypical variations in air contents should be investigated.

Despite this experience, cases are still periodically seen of admixtures being incorporated in a way which could generate a repeat of this marble-cake concrete.

Cases have been seen, for example, where the admixture hoses were discharging into the mixing bowl alongside the water supply line. This system relied on the unrealistic expectation that effective dilution would occur by mid-air collision.

The dilution of admixtures must clearly be by positive and controlled means. One method is to discharge them (separately) into the water tank. Where admixtures are discharged into the water-supply line, their injection must have a suitable separation of time and/or distance.

Batch delivery docket

The certificate must record the details required to establish the time of "completion of batching" as defined in Annexure R83/5. Subsequent addition of water (retempering) .... must be deemed to have taken place after completion of batching.

The following issues are basic to the application of this clause:

(i) Under Annexure R83/5, “completion of batching” is defined in various ways according to the method of mixing and transport.

17 AEA = air entraining agent. WRA = water-reducing admixture.



Ed 2 / Rev 0 29

(ii) Mixing does not commence until all ingredients have been added. Hence, the commencement of mixing cannot occur before the completion of charging.

(iii) In the case of mobile mixers (agitators), it is common practice for the driver to pull away from the batch station to carry out mixing and (if necessary) adjustment of the slump. For the practical application of this clause (including surveillance thereof), it could normally be taken that “the completion of charging” occurs when the truck leaves the batching bay.

(iv) As long as slump adjustment is completed at the batch plant (and within 10 minutes) then this is deemed to form part of the batching operation. In other words, any added water is considered to be water which should have been added by the plant. This interpretation obviously relies on other conditions like minimum remixing times and slump limits being complied with.

However, any addition beyond this point is deemed to have occurred beyond the “completion of batching” and hence constitutes retempering, and must therefore comply with Clause A4.2.2(f).

(v) The practical and effective application of the R83 clauses relating to the batching, mixing and forming times relies on the reliable recording of the timing of operations which define “the completion of batching”.

The delivery dockets from pre-mix plants commonly contain an entry titled “despatch time”. However, in some plants (including high-turnover computerised plants) this may merely indicate the time at which the docket was printed (which can be either before or after batching) and so it should be assumed that this bears no contractual correlation with the batching operation.

The critical timings are as shown in Plate 4.5 and these must be recorded on the delivery docket in order for these clauses to be properly applied and controlled by the contractor.

Because of the logistics associated with batching and the printing of dockets in high output plants, it may not be practical to require that these items be printed by the computer. Hence, it would be satisfactory for the driver to write them on the docket, on the condition that it is done in a regulated manner as agreed between all parties. Under these conditions, surveillance and auditing would be a reasonably simple operation.

In cases (b) and (c) of Plate 4.5, both of the following items must be noted on the docket:

(A) time of completion of charging, and;

(B) time of completion of slump adjustment.



30 Ed 2 / Rev 0

Plate 4.5 – Completion of batching

Mixer & transport types Timings

(a) Stationary batch mixer discharging into a tipper or storage bin

Time of discharge from the mixer.

(b) Stationary batch mixer discharging into a mobile mixer (agitator)

Completion of charging of the stationary mixer (i), plus 10 mins;

or completion of slump adjustment at the batch plant;

~ whichever occurs first.

(c) Direct charging of a mobile mixer (agitator)

Completion of charging (ii), plus 10 mins;

or completion of slump adjustment at the batch plant;

~ whichever occurs first.

(d) Continuous mixer discharging into a tipper

Time of commencement of discharge into the truck.

(e) Continuous mixer discharging into a storage bin

Time of earliest discharge (from the mixer) of that concrete within the bin (iii).

Notes (i) This relates to the charging of the stationary mixer, i.e. ignoring any subsequent addition to

the mobile mixer at the slump stand. (ii) Under normal operating conditions, “completion of charging” can be taken as the time at

which the truck leaves the batching bay. (iii) If the bin is continuously charged without being fully emptied on a regular basis, the relevant

issue will be the age of the oldest portion of mix within the bin at any particular time.

Plate 4.6 provides a graphical representation of the specification requirements relating to Case (a) of Plate 4.5.

Plate 4.6 – Process time controls for Case (a) of Plate 4.5

Charging Completion of batching

Mixing

Mixing time as per mixer

uniformity testing

Discharge

Haul

Finish, texture & cure

Spread, compact & form

Contractor to nominate & monitor under Cl 4.2.2

Batching

Forming time



Ed 2 / Rev 0 31

Plate 4.7 provides a graphical representation of the specification requirements relating to Cases (b) and (c) of Plate 4.5.

Plate 4.7 – Process time controls for Cases (b) & (c) of Plate 4.5

Consistence (slump)

Consistence must be tested by the slump test.... within 30 or 40 minutes of the completion of batching ....

The intent of this clause is as follows:

(i) to ensure that the original batched mix (prior to any subsequent drying and/or retempering and/or significant hydration occurs) has a complying slump; and

(ii) in the event that a load is batched too wet, to prevent its being stood aside long enough for the load to dry back to a conforming slump; see further discussion in Sections A4.2.2(f).

If the concrete temperature is less than or equal to 25C then a time of 40 minutes is allowed because concrete dries back slower at lower temperature.

Under Clause 4.2.2(f), once a batch yields a nonconforming slump it cannot be incorporated into the Works (but see clarification hereunder). In other words, it cannot be dried back into conformity. Further, under Clause A4.2.2 (18) nor can additional new ingredients be added in order to “dry out” the batch.

The following clarification is required regarding judgement of slump conformity:

(A) Under Clause A4.2.2(h) one re-test is permitted after a failure, on the condition that it is carried out “immediately” (i.e. before significant drying occurs).

18 Clause A4.2.2 states that “... after the completion of mixing, the entire batch must be discharged ... before

any further charging takes place.” Clearly this practice of “topping up” results in some of the mix exceeding its forming time. Concrete placers typically refer to these as “hot loads”.

Charging Completion of batching

Mixing #1

Mixing time as per mixer

uniformity testing

Adjust slump

Haul

Finish, texture &

cure

Spread, compact &

form

Batching

Forming time10 mins max

Retempering

Haul time

Mixing #2

Mixing time

Delivery time

Discharge

30 mins max



32 Ed 2 / Rev 0

(B) If a low-slump failure is encountered, the load may be retempered and re-tested, as long as it is within the time limits of Clause 4.2.2(f). See further discussion under Section 4.2.2(f).

Consistence must be .... within the following limits:

10 mm for slipformed concrete

15 mm for manually placed concrete.

These limits are consistent with AS1379.

Forming time

The Contractor must determine a “maximum forming time” …. for each nominated mix..

The forming time is the time between “completion of batching” and final forming. By definition, it includes forming (as in “slipforming” and “hand forming”) but excludes hand finishing and texturing.

The intent is that the contractor will regularly monitor the paving conditions and nominate a maximum concrete age beyond which paving is unlikely to consistently and reliably satisfy the assessment criteria. These criteria are detailed in Clause A4.2, with the key issues being:

the supply of a homogeneous end product (i.e. pavement), and

concrete workability (at the time of paving) which is compatible with the capacity of the equipment to achieve the specified compaction and surface condition with only nominal hand finishing (19).

In other words, if the mix is too dry to be placed, compacted & formed etc. to satisfy the requirements of Clause A4.2 then, by definition, it has exceeded its "maximum forming time".

It is considered unrealistic to prescribe a fixed limit on working time (such as 90 minutes) because:

this may be too liberal under hot summer conditions but unnecessarily restrictive in mild conditions;

a mix which is too old for hand paving may still be acceptable for slipforming;

a high-energy slipformer may readily cope with a mix which is too old (and dry) for a lower power paver;

one concrete mix could be unworkable after 60 minutes whilst another (under like conditions) could be readily workable at 90 minutes or beyond.

However, there are risks associated with paving old batches and hence Clause 4.2.2(h) requires the contractor to demonstrate the conformity of such loads.

Notwithstanding, contractors are given substantial latitude to plan and manage their paving operations to suit their own circumstances.

In establishing the maximum forming time, the intent is that the contractor will take into account issues such as weather conditions and the type of equipment being used, and its capacity to handle concrete of various ages. If properly applied, the forming time would be varied throughout the day to account for significant changes in local conditions.

19 See also Section 4.3 for a discussion of the issues which should be addressed in assessing the success (or

otherwise) in achieving “the specified finish”.



Ed 2 / Rev 0 33

If slipforming and hand paving were in progress simultaneously, it is likely that the forming time would be different for each.

The forming time can be regulated by management of aspects such as

mix design;

admixture selection and dosage;

selection of paving equipment, and its adjustment and maintenance;

co-ordination of delivery trucks, haul conditions and site logistics.

In practice, there may be various ways of assessing the forming time. One common way is to walk back from the paver and regularly assess the condition of the concrete by touch test. At some distance from the paver, the concrete will reach a condition where an experienced assessor will judge that the paver would not cope well with a batch in that condition. Based on information contained on the tally sheets, an estimate can be made of the age since “completion of batching” for that section of concrete. The forming time would be derived by applying a reasonable safety margin (i.e., reduction) to that age.

In applying these criteria, concrete beyond that age which is still in the truck must not be discharged for incorporation into the Works. Where concrete has been discharged within the forming time but, because of delays such as paver breakdown, it has not been “formed” within the forming time (20), its conformity must be proven in accordance with Clause 4.2.2(h).

However, other criteria may also be applied to assess conformity. For example, if excessive slurrying is required in order to achieve the specified surface finish, the product might be deemed nonconforming under Clause 4.3.5.

Supervisors should also be alert to the risk that older batches (with reduced slump and workability) will also be more susceptible to defects such as slotted voids above tiebars; see Section A4.1.2 for discussion.

Plate 4.8 shows an example of excessive slurrying. The concrete in these photographs was 90 to 120 minutes old and was clearly not “compatible with the capacity of the paving equipment .... to achieve the specified surface finish” (21) without excessive slurrying and manual finishing.

Evaporation retarder was splashed over the surface behind the conforming plate in order to generate sufficient slurry with the oscillating screed to fill the excessive surface voids. Several passes of the paver were required in order to produce the surface shown in Plate 4.8.1.

Further retarder was splashed over the surface behind the paver in order to assist with final hand finishing (Plate 4.8.2). This retarder was trapped in the workers’ footprints when fresh mix was added over the top.

Surface delamination became evident on this project prior to its opening to traffic, as shown in Plate 4.8.3.

20 See the definition of “forming time”. 21 See Clause A4.2(c).



34 Ed 2 / Rev 0

Plate 4.8.1 Excessive evaporation retarder has been applied in order to achieve adequate slurry under the oscillating screed.

Plate 4.8.2 Evaporation retarder ponded in workers’ footprints.

Plate 4.8.3 Surface delamination on this project.

Plate 4.8 – Excessive use of evaporation retarders

As further demonstration of the impact of “forming time”, Plate 4.9 shows a section of pavement which appears to have been paved beyond the maximum forming time. The area has required substantial slab replacement at less than 10 years of age, and further premature failures are imminent.

In manual paving, the same principles apply. Particular notice should be taken of whether the mix does actually become workable under the action of internal vibration and that the vibrating screeds are effective in producing “the specified compaction and surface finish” (21) without excessive hand finishing.

If these aims are not achieved then, by definition, the mix has exceeded its acceptable forming time and hence is nonconforming. The contractor must review his maximum forming time to prevent a recurrence. (This is assuming that the mix is workable when placed within shorter forming times and does not require design adjustment.)



Ed 2 / Rev 0 35

Plate 4.9.1 General view of slab replacements. Note the lateral step in the median edge where major paver changes appear to have been made.

Plate 4.9.2 The kerb recess was transitioned “on the run”, presumably using a bolt-on form.

Plate 4.9.4 The original slabs exhibit extensive fine plastic cracking which (in the replaced slabs) appears to have linked up into full structural cracking.

Plate 4.9.3 There are clear signs that the maximum forming time had been exceeded when paving recommenced.

Plate 4.9 – Forming time

4.3 PAVING CONCRETE

The construction of high-speed highway surfaces requires closer control than most other concrete applications. This is driven by the need to achieve a high level of ride quality on a surface which balances high-speed friction values with low noise emission. We also require a high level of durability of these surface properties and of the structural integrity of the pavement.

These criteria will only be met through adherence to higher standards of paving practice than those which are typically used in the general construction industry.

4.3.1 Slipform (Mechanical) Paving

A brief discussion on the principles of compaction is provided in Section 5.2.

The mechanical paver must spread, compact, screed and finish the freshly placed concrete so as to produce a dense and homogeneous slab with a smooth uniform finish requiring a minimum of hand finishing.



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Uniformity is a fundamental requirement of all manufacturing and construction operations. One of the major benefits of mechanical paving over manual paving is that, as long as the fundamental paving techniques (22) are sound, then the process is more likely to produce a uniform and conforming product (23).

However, it would be unrealistic to expect that a slipform paving operation will proceed without intermittent problems and so regular surveillance is essential, particularly given that outputs can commonly be around 600 m2 per hour. Surveillance should watch for significant changes in the quality of the paved slab.

If the paver is operating as designed, and the mix has been designed to suit that specific paver then the paved slab should require a minimum of hand finishing. A moderate amount of work may be required along the edges, but if substantial bull-floating is required on a regular basis then it is a good indication that the mix and/or the paver require attention.

Intensive hand finishing invariably impairs the final ride quality, but the major concern is that the surface problems may be an indication of other serious problems within the slab which will not be corrected by even the most intensive bull-floating. Plate 4.10 shows examples.

Under the Quality System requirements, the contractor is responsible for detecting and investigating all irregularities such as those shown in Plate 4.10. Clause 8.6 of Specification Q6 states:

“Identify and control all products or services that fail to pass any inspection or test in accordance with the defined acceptance criteria.”

Additionally, Clause 7.5.3 of Specification Q6 states:


Plate 4.10.1 Edge finishing will commonly be required but a need for bull-floating (as seen being carried out from the work platform) on a regular basis is an indication of problems with the mix and/or the paver.

22 In this context, “processes” includes aspects such as mix design, concrete quality/uniformity (as supplied),

paver design/setup and its operation. 23 By comparison, hand paving is inherently more variable because of the higher degree of human

involvement in operations such as vibrator use. However, this should not be construed to mean that hand paving cannot be of a high standard; there are many examples of fixed-form paving around NSW which is of a significantly higher standard than much of the slipformed work.



Ed 2 / Rev 0 37

Plate 4.10.3 (above) Subsequent coring yielded the voided specimens shown above. The cause is thought to have been a sporadically operating vibrator.

Plate 4.10.2 (left) Surface voids were a recurring feature within the longitudinal bandwidth shown marked.

Plate 4.10 – Compaction and surface finish

These requirements are reinforced in Clause 4.3.1 for the specific case of paver interruptions, as follows.

Should subsequent testing at the location of an interruption indicate the presence of non-uniform or nonconforming concrete, such concrete must be removed and replaced

The emphasis on uniformity stems from the reality that, even under the most favourable slipforming conditions, there will be intermittent events which disrupt the continuity and uniformity of the work. This is probably best demonstrated using a production-line analogy.

During a period of ideal slipforming, it would be reasonable to describe this as a repetitive (somewhat automated) operation resembling a production line process. However, as soon as paving is interrupted (by a delay in concrete supply, for example) human intervention dominates the automated functions and hence it should no longer be assumed that the product will be homogeneous.

In other words, if it becomes necessary to stop the paver, the operator has to intervene with actions such as throttling down the vibrators. Upon resumption, those operations must be reversed. This is effectively a disruption to the production-line process.

Transverse construction joints are the most pronounced examples of disruption to the paving process, hence they are treated in R83 as separate processes and are defined by separate “transition” lots.

At locations .... such as .... transverse construction joints .... where the paver is unable to fully compact .... the concrete, supplementary manual vibration must be used.

Transverse construction joints are a source of frequent failure. CRCP has proven to be especially susceptible to this, but there is no reason why the same problem should not occur in jointed pavements (such as PCP). Transition zones were introduced to R83 in order to address the high incidence of failure in this area.



38 Ed 2 / Rev 0

The highest risk exists at start-up of paving (rather than end-of-day) because the paver can rarely be positioned such that its vibrators will compact the first few metres of the pour. Plate 4.11 shows a typical failure, in this case in CRCP. Note that the failure is several metres from the joint, consistent with the fact that the vibrators would be sitting further than this from the joint when the paver is positioned against the previous pour.

Hence, manual vibration (as shown in Plate 4.11) must cover the full area which has been missed by the paver’s vibrators and it is not good enough simply to vibrate along the edges.

Clause 5.2.1 requires that the areas within 3 m of the joint be treated as Transition Sublots, but some contractors may have to manually vibrate more than 3 m if their slipformer leaves a larger length uncompacted. Under Clause A4.3.3, contractors are required to nominate this length for their specific paver, and this should be closely checked during the paving trial.

Plate 4.11.1 Failure in CRCP caused by poor compaction within the Transition Lot.

Plate 4.11.2 Supplementary manual vibration is not only required along the near edge but over the whole area not vibrated by the paver.

Plate 4.11 – Compaction in Transition Lots

4.3.2 Manual (Fixed-Form) Paving (24)

It is as difficult, or more, for an artist to paint a miniature as a large canvas (25).

Two common misconceptions regarding manual paving are that:

it will necessarily give a poor ride quality, and;

it will be of lower overall quality than slipformed paving (and hence will give poorer long-term performance).

Both of these views can be soundly countered from wide experience around NSW (and elsewhere).

Regarding ride standards, there are several hand-paved projects around NSW with roughness values of around 55 counts/km, with some as low as 45 to 50 counts/km (26). These values are lower than much of the slipformed paving which has been completed within the same period.

24 ~ also commonly referred to as “hand paving”. 25 Dame Margot Fonteyn 26 In one project, very good results were achieved by using three passes of the vibrating screed in lieu of the

usual two passes.



Ed 2 / Rev 0 39

In terms of overall quality, some of the best performing pavements constructed in NSW since 1975 were hand paved. This particularly applies to CRC pavements (27).

Notwithstanding these comments, it is also true that hand paving is more susceptible (than slipforming) to high variability, because of its non-automated nature. In other words, the risks associated with hand paving are higher, and this should be reflected in a higher level of surveillance and auditing.

The key issues are:

For ride quality: accurate levelling of formwork;

correct use of vibrating screeds.

For overall quality: correct use of vibrators and screeds;

control of the supplied mix, especially thoroughness of mixing.

Forms must be mortar tight .... They must be set to tolerances equivalent to those specified for the finished base surface.

Ride quality will depend very much on the accuracy of formwork placement, and on the accuracy of screeding.

Forms are generally timber, steel or a composite of both. For high quality work, forms should be set to tolerances at least equal to those specified for the finished surface because the screeding process will dictate the surface profile, and finishing operations can do little to correct poorly controlled screeding. Formwork straight-edge tolerance should be better than 3 mm in 3 m.

27 One example is stage 1 of the Clybucca CRCP. It was constructed in 1975 by manual methods (and

inexperienced crews) and has not suffered a single failure within the 5.5 km length. Roughness counts were of the order of 70 counts/km. Manual paving carried out since that time by experienced contractors has achieved roughness counts as low as 45 to 55, which is substantially smoother than much of the slipformed work.



40 Ed 2 / Rev 0

This standard of formwork yields .... .... this standard of compaction.

Plate 4.12 – Formwork and compaction

Plate 4.13.1 For vibration to be effective, the concrete must be confined by forms (or by sufficient surrounding concrete to prevent lateral movement of the zone being vibrated). If the concrete is moving sideways, the vibration energy is being wasted in terms of expelling entrapped air.

Plate 4.13.2 Gaps under formwork allow the loss of mortar, hence the edge will not comply with Clause A4.5.1 which requires that: “the first-placed face must be dense and fully compacted and be free of honeycombing ....” A strip of plywood along the bottom edge would be suitable in this case.

Plate 4.13 – Formwork and compaction



Ed 2 / Rev 0 41

Example of good formwork design and fixing. (In the example at left, the internal braces will be removed prior to paving.)

Plate 4.14 – Formwork

To achieve the required standards of compaction and surface tolerance, it is necessary to use both internal and surface vibration. Non-vibrating screeding techniques are unable to achieve adequate compaction and have proven unacceptable in structural applications such as paving. The literature also suggests that their shearing action may encourage plastic shrinkage cracking. The continued use of non-vibrating screeds in general construction work should in no way be taken as an indication of their effectiveness.

Similarly, vibrating screeds alone (without prior internal vibration) are unable to achieve compaction throughout the full depth of the slab, and advertising claims to the contrary should be treated with extreme caution.

Correct placement and compaction procedures are therefore as follows:

(a) place and spread the mix into its final position (with shovels), and then commence:

(ii) internal vibration, then

(iii) surface screeding and vibration (2 passes minimum).

(a) Documented process controls

Minimum vibration criteria have been included within the specification in response to frustration at the ongoing high variability in practices and standards throughout the industry.

The Principal requires that the person in charge of the paving crew and at least half the remainder of the crew present at each separate concrete paving work must have undertaken the RMS “Concrete Paving Crew Training”. The training course covers activities such as setting formwork, stringlines and reinforcement; compacting concrete; placing and finishing concrete.

Extensive experience over the past 20 years shows that compaction is one of the most important of the processes which “directly affect quality” of concrete paving. Hence, there should be no doubting that the requirements of this clause are applicable to the compaction process.

However, the contractor may not always recognise what processes are critical or that they require documented procedures. RMS specifications often therefore specify those processes, and may also identify particular aspects of the process.

For compaction, these procedures are set out in R83 Clause A4.3.3.



42 Ed 2 / Rev 0

(b) Internal vibration

Extensive experience shows that one 50–70 mm vibrator working continuously can fully compact only 10 m3 per hour. Hence, if concrete is being placed at the rate of 30 m3/hour, then 3 vibrators will be needed, and they must be working continuously.

Vibrators can be dragged (as they are under slipformers) or “poked” but, in both cases, the compactive effort must be thorough and systematic.

The complexity of concrete rheology is such that there are no formulae to calculate the required amount of vibration for a given mix. So (as in cooking), one option is to begin with a sound basic “recipe” and to refine it with experience and testing [19].

For pavements (and other major structures such as bridges) worth millions of dollars and which are expected to provide low-maintenance service in harsh environments for many decades, it must be accepted that a substantial effort is warranted to test and refine these recipes to achieve conforming results. Hence, the minimum criteria in the specification should be regarded merely as beginner’s “recipes”, as a starting point for controlled trials at the start of a project.

The recipes allow vibrators to be inserted or dragged, and they provide guidelines on insertion spacings.

If the vibrator is dragged, its speed should not exceed 1.5 m/min. A slipformer has trouble achieving good compaction at speeds exceeding about 1.5 m/min and so there is no reason to expect that a manually operated vibrator will be any more effective.

If the vibrator is poked, its withdrawal must be very slow to ensure that voids are not left in its path.

Segregation due to over-vibration is highly unlikely in well designed paving mixes (such as those complying with RMS specifications) and the international literature indicates that it is very rarely seen.

In SFCP, compaction is just as important as in plain concrete. In addition to the usual benefits of good compaction, SFRC requires full and consistent compaction to achieve high fibre bond strength. See also ACI recommendations in Section A8.8.

The concrete must then be compacted by internal vibrators with the following operating parameters:

A brief discussion on the principles of compaction is provided in Section 5.2.

The specification provides three broad techniques which can be used for the internal vibration of slabs. (Method 2M is simply a modified version of Method 2.) The operating parameters provided therein are guideline values which have been found to give satisfactory results under typical conditions. They should be verified or revised by the contractor for specific site conditions.

Each method is controlled and systematic, and hence satisfies the intent of achieving a uniform result throughout the Lot.

Unfortunately, however, it is more common to see a third method in use. As depicted in Plate 4.15, Method 3 comprises the random and unsystematic use of vibrators at variable spacings and durations. For several reasons it is nonconforming and unacceptable.



Ed 2 / Rev 0 43

Plate 4.15 Methods 1 and 2 are systematic and acceptable. Unfortunately, Method 3 is more common, but is nonconforming in several regards.

Plate 4.16 Random insertions (marked ) are nonconforming. Vibration too close to a leading edge will only cause spreading of the mix and so does not constitute compaction.

Insertions; randomin this case

Insertions tooclose to an edge

The notation “X” in Method 3 shows vibrator insertions which are too close to the leading edge of the pour. In these locations, the vibration energy is wasted in creating lateral movement of the concrete (i.e. spreading) and is therefore essentially ineffective in terms of compaction.

Of Methods 1 & 2, dragging offers the following benefits over poking:

it is more efficient because the vibrator spends less time out of the concrete;

there is less likelihood of generating the voids which are often left by too-rapid withdrawal;

it is likely to be more systematic than poking;

it is less tiring for the operators, hence is more likely to be done thoroughly.

These benefits apply to all applications of slab-on-ground paving, and particularly to thinner slabs where poking is inefficient and where incomplete immersion of the head will increase the risk of burn-out from over-heating.

In reinforced slabs, the drag method requires minor modification (as per Method 2M) but is still the preferred option.

Regardless of the method being used, its features should be assessed in accordance with Plate 4.17 for full compliance with the specification (and with long-established good practice). If it fails on any one criteria then it must be modified.



44 Ed 2 / Rev 0

Plate 4.17 – Checklist for vibration techniques

Criteria Requirements Judgement or

(a) Systematic Uniform and thorough coverage of the full Lot (i).

(b) Vibration time Long enough to ensure conforming and uniform compaction levels (i).

(c) Spacing Close enough to ensure consistent conforming compaction between dips/drags (i).

(d) Withdrawal Very slow, to ensure full recompaction in its own void. Withdrawal speeds above 1.5 m/min may be excessive (ii).

(e) Spreading If the vibration is causing lateral spreading of the mix then this vibration time doesn’t count as “compaction” (iv).

(f) Disturbance No disturbance (after vibration) which may create voids (iii).

Notes (i) The technique should be in accordance with Method 1 or 2 (or 2M). Alternatively, the contractor may

demonstrate the conformity of an alternative technique which satisfies all requirements of the specification and this table.

(ii) There is very little vibrating influence beyond the tip of the vibrator (along its projected axis). (iii) Disturbed areas (e.g. footprints) must be re-vibrated, possibly by screedboard. (iv) “Spreading” indicates a waste of the vibration energy. It doesn’t yield effective compaction and it risks

causing segregation.

Plate 4.18 provides an example of the practical application of the criteria listed in Plate 4.17. (1) Vibration this close to the leading edge will

merely spread the mix without providing effective compaction and so is a wasted activity which is better carried out by shovels.

(2) This vibration will be effective as long as criteria A, B, C & D are satisfied.

(3) Walking in the vibrated mix constitutes disturbance (Criteria F) because it introduces new voids. For these voids to be effectively removed, the vibrating screeds must be operated using the recommended parameters of frequency & speed etc (28). Disturbance should be avoided at all cost after the first screeding pass. Raking ahead of the second screed should be with long-handled hoes (or similar).

Plate 4.18 – Manual compaction

During the pour in Plate 4.18, a third vibrator operator was working intermittently but was also spreading the mix near the leading edge, without achieving effective compaction. Hence, only one of the three vibrators was achieving worthwhile compaction. The paving output was between 20 and 30 m3/hr (which typically requires 2 to 3 vibrators), hence it is unlikely that this concrete was

28 The term “recommended” is intentionally vague here. With some screeds, it would be safe to follow the

recommendations of the manufacturer, but this is not universally the case. For example, claims that vibrating screeds can effectively compact slabs up to 300 mm thick (without prior internal vibration) are rarely verified and so should be treated with great caution. Further guidelines are provided in the RMS Concrete Pavement Manual[3].



Ed 2 / Rev 0 45

being adequately compacted. If results for this standard of work are commonly achieving 99-100% relative density then a check should be carried out to ensure that the reference specimens are being moulded in accordance with Test Method T304.

(c) Surface vibration

Two passes of a vibrating screedboard are required in order to achieve a consistently high standard of finish. This is analogous to using a pre-spreader plus a paver, as indicated in Plate 4.19.

The first screed pass is used to level the mix.

The second pass is required to achieve final surface tolerances and to finish compaction of the concrete in the upper zones, including those areas disturbed by workers' boots.

Plate 4.19 Spreading and paving techniques

internal

and

surface vibration

Concrete pavements require both:

compaction at depth pre-spreading surface compaction & finishing

The front screed (like a pre-spreader) can be used in a stop/start manner if concrete supply is irregular. However, the second pass (like the paver) should be operated in slow continuous movements in order to optimise the ride quality. Hence, the second screed should be left behind until the front screed has provided enough length for a long steady pass.

On each pass it is important that a small surcharge be maintained ahead of the screed because it is this surcharge which transmits much of the vibration into the slab.

A dense and homogeneous slab must be provided, with a surface finish which requires a minimum of hand finishing.

Consistent with slipforming, if substantial bull-floating is required on a regular basis to achieve a tight compacted surface behind the vibrating screeds then it is a good indication that the mix and/or the screed require attention. (See also Plate 4.10.)

Power trowelling of the surface will not be permitted.

The reasons are as follows:

(i) Power trowelling produces a steel-float finish which defeats the intent of achieving a sandpaper-like surface (for friction purposes).

(ii) It is impractical on road pavements because trowelling cannot be undertaken until long after curing should be in place (to prevent plastic shrinkage cracking).



46 Ed 2 / Rev 0

4.3.3 Placing and Paving Operations

Because of precedent, specifications R83/84 assume that the underlying layer will be LCS. If this is not the case then careful consideration needs to be given to issues such as interlayer debonding and the potential loss of moisture and/or mortar into that layer from the Base concrete.

Hence, for example, if the underlying layer is a granular or permeable layer (not LCS), there may be a strong warrant for applying a sprayed bituminous seal.

Plate 4.20 provides a summary guide as demonstration of the type of factors involved. Each situation must be assessed differently, and specialist advice should be sought.

Plate 4.20 – Interlayer Issues

Subbase type (and risk level)

Issues Granular (i) DGAC (ii) OGAC NFC

Moisture loss high low high high

Mortar loss (iii) medium low high high

High bond (iv) medium medium high very high

Possible treatment bituminous seal wax or bitumen

emulsion bituminous seal

or geotextile geotextile

Notes (i) Properties will vary markedly with material types and treatments like stabilisation. (ii) Properties will vary with age & modulus, and with surface porosity. (iii) Mortar loss will compromise the integrity of the Base and will induce high bond. (iv) High bond increases the risks of unplanned Base cracking and yield of reinforcement (e.g.

tiebars).

The subbase surface must be .... clean and free of loose or foreign matter.

Under a concrete base, a thin coating of dust would not be cause for concern because interlayer debonding is desirable. However, deposits of materials like loose sealing aggregate will reduce the effective thickness of Base and so will invariably be nonconforming.

4.3.4 Temperature and Rain

(a) Low temperatures

Lower temperature limits are imposed because concrete is unlikely to develop full strength if allowed to reach low temperatures. RMS has experienced sites where the concrete temperature within the first few days reached values close to zero and thereafter failed to develop adequate strength, even at advanced ages. In one case, core strengths remain in the range 22 to 25 MPa at ages beyond 10 years.

These were typically cases where concrete was placed on cold ground in frosty conditions and where only a light plastic cover was used over the slab.



Ed 2 / Rev 0 47

(b) High temperatures

Similarly, there is ample experience to show that paving at high ambient temperatures leads to a high risk of unplanned cracking. In some cases, this appears to be associated with the plastic behaviour of the concrete at elevated temperatures.

In other cases, it appears to be related to the impact of the overnight temperature drop which can generate very high curling stresses because of the severe temperature differential through the thickness of the slab.

(c) Rain

Rain damage affects not only the surface texture but also the water/cement ratio within the top few millimetres. The strength of this surface mortar is critical to the durability of any surface texture which might be achieved after the rain passes.

Wet surfaces invariably lose the surface mortar within a few years, leaving an exposed aggregate finish, and this is likely to have a reduced friction value. See Section 4.3.8.2 for further discussion on rain.

4.3.5 Prevention of Moisture Loss

Moisture loss can occur from all sides of the paved slab, including the underside.

Hence, if the underlying layer is a granular or permeable layer (not LCS), there is a strong warrant for sealing that layer. See Section 4.3.3 for further discussion.

Should the Contractor elect to use an evaporation retarder to restrict the evaporation of water, it must be applied by a fine uniform spray. Any subsequent finishing operations must be carried out so as not to incorporate the evaporation retarder into the surface mortar.

The prevention of excessive moisture loss from the concrete surface is paramount to minimising the formation of plastic shrinkage cracking.

Figure A3.2 provides guidance on calculating the loss for various levels of humidity, concrete temperature and wind velocity. ACI 318 indicates that a safe upper limit for evaporation loss is about 1.0 kg/m2/hour but a contractual limit is not specified because some mixes have been observed to crack at rates as low as 0.6 whilst others have been placed at rates up to 1.8 without cracking.

It is important to measure actual values of temperature, humidity and wind velocity on site because some seasons may give high evaporation rates even though the climatic conditions seem mild. For example, on relatively mild days in spring and autumn, the evaporation loss can exceed 2.0 kg/m2/hour if a significant wind is blowing or if wind is funnelled through a constriction such as a cutting or under a bridge.

Lower temperature at surface

Higher temperature at base

Tensile stresses



48 Ed 2 / Rev 0

There are few options available in periods of high evaporation potential. The safe option is to cease paving. Alternatively, an evaporation retarder such as aliphatic alcohol can be used. However, it should be realised that they might have mixed success in severe windy conditions.

If sprayed retarders are used, they require close control. In brief, they can significantly reduce plastic cracking if used correctly, but it should also be realised that they are only a temporary solution and the best deterrent to evaporation is a good curing compound uniformly applied at the right time. If the retarder is used inappropriately, it can delay texturing and curing operations and hence may actually increase the risk of plastic shrinkage cracking.

Additionally, it can cause serious damage to the surface if it is used incorrectly, by actions such as slurrying it into the surface mortar; see Plate 4.21.

Site staff should also be alert to the temptation to use evaporation retarders to counter the problems associated with non-uniform drying of the concrete surface. This is sometimes apparent during floating and/or tining when some areas will be dry while adjacent areas will appear significantly wetter. The dryer areas will sometimes be prone to plastic shrinkage cracking.

Variability of this sort will often be related to inadequate mixing of the concrete, and this should be investigated as a first step, particularly where delivery is by mobile mixers; see Section A4.2.2 for further discussion. If poor mixing is the real cause of the problem then evaporation retarders will not be the appropriate treatment, and their use will only exacerbate the potential problems mentioned above.

Plate 4.21 Evaporation retarders were used excessively on this project. Surface scaling began to occur even before opening to traffic.

Aliphatic alcohol is typically diluted with 9 parts of water to assist in its application. Floating of a surface which is covered with this mixture will effectively slurry it into a high water/cement ratio mix.

Given the fact that texturing is of the order of only 2-3 mm, the strength of the surface slurry is critical to its durability.

As an alternative to accepting the use of retarders, another proven strategy is to lengthen the texture tines in order to allow earlier texturing close behind the paver. This allows curing compound to be applied as soon as the low-sheen condition is reached and may avoid the need for retarder.

Plate 4.22 lists statements which might be found on the technical data sheets for evaporation retarders, together with cautions about those comments.

Retarders should be viewed as merely a single component of an integral paving operation. They should not be viewed as a cure for other ills and, by review of other operations, it may be possible to avoid the difficulties associated with their use.



Ed 2 / Rev 0 49

Plate 4.22 – Use of evaporation retarders

Statement RMS Comments

“.... reduces surface moisture evaporation …” Agreed, if used appropriately.

“.... should be applied immediately after screeding while surface moisture is still present ....”

Agreed, the compound is most effective when there is surface moisture on which it can float.

“.... the surface closes better under the trowel giving an improved finish ....”

This may be true, but trowelling of a wet surface constitutes slurrying.

Also, if intensive trowelling is required then adjustment should be made to the mix; see Sections 4.3.1 & 4.3.2

“.... eliminates the need to add extra mixing water to compensate for evaporation during finishing ....”

If conditions are so extreme as to warrant extra mixing water then the retarder is unlikely to prevent cracking, and paving should cease.

“.... it may be advisable to apply additional (product) after each finishing operation.”(ii)

This encourages slurrying of the surface and is not acceptable practice.(i)

“.... abrasion resistance and durability are not affected ....”

This claim is untenable if one accepts that durability is reduced with increasing water/cement ratio.

“.... is not a curing agent ....” Agreed. If possible, apply curing compound rather than retarder.

Notes (i) There is no harm in applying the retarder several times as long as it is not worked into the surface mortar. (ii) It should not be necessary to routinely apply several sprays. For example, there is no justification for

spraying immediately behind the paver if bull-floating will follow soon after. It would be preferable to complete the floating and then spray the retarder.

In summary:

Do

use evaporation retarders if the conditions warrant, but:

regularly review their use when conditions change, and:

consider other alternatives (such as revised tining and curing procedures).

Don’t

use them to compensate for other problems (such as a dry, unworkable mix);

use them unnecessarily in mild conditions (because they will merely delay the tining and curing operations);

waste them by applying more than is required (a few light sprays may be more effective than a single heavy one);

slurry them into the surface.



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4.3.6 Texturing of Surface

Most concrete surfaces will be textured with a combination of hessian drag (29) (longitudinal) and transverse tining.

A hessian drag generates microtexture (for skid resistance) by enhancing the sandpaper-like surface provided by the 40% sand content;

The tining provides channels for water dispersion in order to prevent aquaplaning.

In brief, it is the microtexture that provides most of the friction, while the tining (macrotexture) merely speeds removal of water so that the tyre remains in contact with the sandpaper-like surface.

Tining is not carried out when the surface will be topped with asphalt.

When assessing tining, the following issues should be considered:

the raised profiles should be at least 10 mm wide to ensure that they don’t break off under tyre loading;

shallow texturing may be less effective in water dispersion, but:

deep texturing will increase tyre/road noise and increase megatexture vibration within the vehicle. (See Section 5.2.2 for further details.)

Plate 4.23 The TRRL Mini Texture Meter

Note that the result obtained from texture testing is the “average” texture depth over the area of the test section. In other words, the actual depth of tining may be 2 to 4 mm but the average depth (as measured) will be less than 1 mm.

Of the two methods of measurement, the TRRL Meter is preferred because it is less operator-dependent. The Meter is walked over the surface at a speed of 3 to 6 kph. A printed output shows the mean depth over each consecutive 10 m length and the average of five 10 m lengths is given at the end of each 50 m section.

Attention is drawn to Table A1.2 (Annexure R83/1) which schedules areas which must be textured differently to that specified in Clause 4.3.6.

For texturing of steel-fibre reinforced concrete, refer to Section A8.5.

29 ~ except for SFCP.



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4.3.7 Curing

The strict curing criteria imposed under R83 are justified by the following factors:

(a) the durability of surface texture is highly dependent on the strength of the surface mortar;

(b) pavements are placed and cured under exposed and sometimes harsh conditions;

(c) by comparison with untextured surfaces, R83 criteria need to be more demanding in order to achieve adequate coverage on all texture faces, including vertical ones.

Plate 4.24 shows the sequence of events in the application of the curing compound.

Hessian drag Tining

CuringBleed waterleaves surface

Slipform Paver

2nd application1st application

10 to 30 mins

Transversetexturing

Plate 4.24 – Work operations associated with curing

The curing compound must .... be applied uniformly in two applications

Two separate applications are required in order to:

(a) reduce the impact of any fluctuating wind which may disperse the spray, and;

(b) minimise the extent of runoff from vertical faces.

The resulting total application from the two sprays is obviously significantly higher than the rate derived from water retention testing (as required under AS 3799). This is intended to compensate for losses from the vertical faces of the surface texture (notwithstanding the lower limit imposed on the material’s viscosity).

The curing compound must .... be applied .... within 15 minutes of the surface reaching the “low sheen” bleed water condition

The time of application of compounds is very important. The best treatment will depend on the type of compound being used (i.e. wax, hydrocarbon etc) but, as a general rule, the optimum time of application is very soon after the surface reaches the low-sheen condition.

In general, if they are applied too early while there is free bleed water on the surface, the bond will be poor and the compound is likely to globulate instead of forming a continuous film.

If they are applied too late, they are again likely to globulate.

Work carried out in the 1980s by Clarke [7] (see Plate 4.25) showed that:

chlorinated rubbers were far more sensitive to late application than were waxes;

waxes performed very poorly if applied too early;

for chlorinated rubbers, the effect of early spraying is not clear but the trend suggests that performance would be reduced;



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The trends support the concept of an optimum application time.

Site staff should be alert to the problem of non-uniform surface drying when it will be apparent that some areas are ready to spray whilst adjacent areas are too wet. This may be an indication of inadequate mixing, and this should be investigated as a first step, particularly where delivery is by mobile mixers; see Section A4.2.2 for further discussion.

(On the graph below, the application times shown on the horizontal axis are totally inconsistent with those which would apply in the field. In other words, application at 2 to 3 hours would be far too late in the field and it can only be assumed that these long delays reflect the influence of controlled laboratory conditions.)

Plate 4.25.1 There is an optimum time for application of curing compounds

Plate 4.25.2 The “hi-sheen” condition indicates the presence of bleed water and is not conducive to good coverage or bond of a curing compound.

Plate 4.25 – Timing of curing

The curing compound must form a continuous and unbroken film.

It should be clear that, to be effective, compounds need to be applied with a uniform and complete cover at a rate not less than that determined by water retention testing.

…the application rate must be 25% higher .... (for) .... the faces of formed joints and sections of slipformed edges which were supported by temporary forms at the time of initial spraying.

Plate 4.26 shows a case where curing has not been applied to the paved edge. Given that cracking often initiates at the edges, it is very risky (and nonconforming) to omit edge curing. Poor curing at arrisses also leads to a substantial reduction in strength and so renders them increasingly susceptible to spalling.

Where the top surface is cured with bitumen emulsion (for subsequent asphalt surfacing), it may be more convenient to cure the edges with wax emulsion.



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Plate 4.26 Curing must include formed edges (but not the reinforcement). Wax emulsion is acceptable on the edges.

4.3.8 Protection of Work

4.3.8.1 Temperature

....for the first 24 hours after placement to ensure that the temperature of the concrete does not fall below 5C.

Water reaches its lowest unit mass (i.e. maximum expansion) at 4C. Fresh concrete which is exposed to this temperature, is likely to suffer frost damage as a result of expansion within the surface zone.

Thermometers used for this purpose must be capable of accurately measuring the surface temperature and not merely the air temperature above the concrete.

4.3.8.2 Rain

The current RMS texture pattern of longitudinal hessian-drag and light transverse tining has been developed over many years to provide a balance of the needs for high friction and low noise emission from a sound and durable surface. There is ample experience to show that rain-affected surfaces do not satisfy these requirements, for the following reasons:

(a) under traffic, the weakened surface will abrade to an exposed aggregate finish, which will rarely provide the required friction properties (30);

(b) it is also possible that joint arrisses will spall to the extent of increasing tyre noise and reducing sealant life.

The assessment of rain damage on a slab requires consideration of several issues, depending on its severity. These issues include:

durability of the surface texture

As a consequence of the higher water-cement ratio, the coarse aggregate is likely to be prematurely exposed and the micro~ and macrotextures may be prematurely abraded (31).

ride quality

The ride quality could be compromised.

30 European style exposed aggregate surfaces (or “Whisper” concrete) are very different because the

aggregate is closely controlled for properties such as size, shape and polishing value. 31 The increased water/cement ratio has two deleterious effects, viz it reduces the concrete strength and it also

substantially increases the curing period required to achieve a sound pore structure. This prolonged curing will rarely be provided because it would be far in excess of the life of most curing compounds.



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Ride quality is relatively easily assessed and so will not be discussed further here.

However, the issue of surface durability is more complex. Potential surface strength indicators (such as the Schmidt Hammer) often require pre-treatment that removes the very mortar which you are seeking to test.

It may be feasible to use the Polished Aggregate Friction Value (PAFV) flat-bed tester, but this doesn’t provide a definitive test result and so is probably best used to provide relative results from a series of samples which includes the doubtful concrete alongside specimens of (known) good surface quality (32).

A discussion of the term “rain-affected” is warranted here because it isn’t always clear whether the addition of water to a plastic concrete surface will be detrimental. This is demonstrated by the fact that “misting” is an accepted form of curing, particularly in the plastic phase (33).

In this assessment, it has to be remembered that the desired surface is a sandpaper finish where the quartz sand particles are held firmly within a strong and durable mortar. The success of the surface (in terms of resistance to abrasion) depends on the integrity of the top few millimetres of mortar, and hence any subsequent significant exposure of the coarse aggregate is likely to require remedial treatment to restore microtexture friction.

In terms of rain, the critical relevant issue is whether the added water is incorporated into the mortar by actions such as floating. Rain is unlikely to have an adverse effect as long as:

the rain/mist falls lightly enough that it doesn’t physically disturb the mortar by (for example) washing the mortar from around the coarse aggregate, or by washing the cement paste from around the sand, and;

the added water is not incorporated into the mortar by finishing operations such as floating, and;

the surface water is allowed to evaporate before subsequent finishing operations are commenced and before the curing compound is applied.

In several regards, the effects of rain are obviously no different from those associated with excessive surface slurrying or abuse of evaporation retarders (see Section 4.3.5).

Given the limitations of the test methods for the hardened concrete, an assessment of the severity of rain damage is best done by close observation (of the above issues) of the concrete in the plastic state. Observations should be recorded in the form of good quality photographs and/or video footage, including close-ups of the condition of the surface mortar.

It is very difficult to repair rain-damaged surfaces to achieve the required surface properties. In many cases, the only viable treatment (apart from removal and replacement) will be diamond grinding. Grinding methods which use other than sawblades are not acceptable over larger areas because they do not provide the required microtexture and macrotexture. (See Section 5.7 for discussion of grinding.)

It follows, therefore, that every reasonable step needs to be taken to prevent rain damage. This means that, prior to the onset of significant rain, the slab needs to have been textured (and

32 Specimens can be prepared by cutting the top from a core sample, then mounting it in epoxy on the

standard PAFV base-plate. 33 Misting is the use of a fog or atomised spray to maintain high humidity conditions around the slab.

Because of its very light nature, it can be used before the concrete is hard enough to support wet covers, and hence is useful in preventing plastic shrinkage cracking.



Ed 2 / Rev 0 55

desirably also cured) and to have developed sufficient strength to support rain covers. These covers need to be effectively weighted against disturbance by wind.

If curing compound was not applied before covering, the plastic covers must be fully secured around all edges in order to maintain a moist environment which will sustain hydration until the compound can be applied. A suitable moist environment will be indicated by the obvious presence of moisture on the underside of the covers. If this is not evident then supplementary water must be provided (with equipment such as a soaker hose under the cover).

At the time of subsequently applying the compound, the concrete should be moist but without free water on the surface, consistent with the optimum condition for spraying fresh concrete.

In order to be able to place covers before surface damage occurs, paving must be terminated a reasonable time ahead of the onset of rain. To this end, weather forecasts should be regularly monitored. Radar maps are available on the Internet.

4.3.8.3 Anchor slabs

The mass of the anchor appears to act as a restraint to thermal curling of the overlying base slab and can induce longitudinal tensile cracking (in the top surface) if the temperature differential is too high.

4.3.8.4 Trafficking of the base

Some of the controls on early trafficking may seem unnecessarily restrictive but it should be remembered that the base will have very low tensile and flexural strengths within the first few days and that it may not be fully supported at the edges if it is subject to thermal curling.

Under these conditions, premature trafficking could initiate harmful micro-cracking. This particularly applies to early edge loading (such as from large concrete saws).

The restrictions also seek to minimise damage to the curing compound and to avoid spalling of arrisses at joints and shrinkage cracks.

tracked vehicles - 15 t/m2 pressure over the track area, with the concrete protected from surface damage.

At first appearance, it would seem that tracks are effective in uniformly distributing their load. However, this is limited somewhat by the following factors:

(a) for a slab in a concave curled condition, the total load imposed on a particular slab may be more critical than the average pressure. A track carrying 10t imposes a high edge load on a curled slab with a low early flexural strength (34).

(b) Whilst a tracked vehicle may distribute its load on soft ground, the same doesn’t necessarily apply on a rigid concrete surface. Examination of a track shows that the load may actually be concentrated into a series of point loads under each bearing. This would impose a high concentrated load as a bearing passes over a localised high point, such as a bullfloating ridge.

34 This is reinforced by the fact that slab self-weight alone can induce flexural cracking under severe curling

conditions within one or two days of paving.



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Plate 4.27 A track assembly on a slipformer.

4.4 CONCRETE PAVING TRIAL

The Trial is an important element in the specification. It is the first opportunity for the contractor to assess the mix under real paving conditions and to trial the process controls on operations such as mixing and paving.

All parties should be clear about the purpose and status of the Trial. The Trial is a limited-length opportunity for the contractor to demonstrate that he is competent in all the operations associated with paving.

However, the Trial:

IS NOT a routine paving run;

IS NOT a practice run or a training exercise;

IS NOT the opportunity to experiment with new techniques or processes.

Too often in the past, the Works have been treated as a training ground on the climb up the learning curve. Acceptance of this approach results in projects of doubtful quality and with a high maintenance demand.

If the contractor requires practice or training then that should be carried out at the contractor’s own site or in a paddock.

An orchestra may tune up on stage, but it doesn’t practise on stage and nor should a contractor be allowed to practise on the Client’s stage. The trial may be used as an opportunity to fine-tune the mix and/or the operations, but it should not be viewed as a practice run.

From RMS’s perspective, the intent of the trial is as follows:

RMS wants assurance that the contractor’s team is competent to carry out the work;

the trial may be carried out at the Site if the contractor wishes, but must be limited in length;

the Principal may accept the Trial for incorporation into the Works if it meets the specification criteria;

if the trial is unacceptable then it must be removed and another Trial will be required before release of the Hold Point. Again, this Trial may be conducted at site or, alternatively, the contractor may elect to carry out the trial elsewhere;

routine paving (over increased lengths) will not be allowed until the completion of an acceptable trial (or trials).

If standards subsequently deteriorate to an unacceptable level then the paving should revert to “Trial” status.

Attention is drawn to the special testing requirements for the trial, as follows:



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Plate 4.28 – Paving trial

Clause Item

A4.1.2.2(ii)(A) Compaction at tiebars

A4.4 Various

A5.2.1.3 Coring in transition lots

A5.2.1.1 Calculation of rolling cylinder unit mass (RCUM)

A5.2.4 Within-core variability

A checklist has been developed for the base Paving Trial; see Attachment C.

Plate 4.29 A paving trial checklist is intended to assist in assessing the Trial.

4.5 JOINTS AND EDGES

See Section A4.5 for a discussion of sealants.

Plate 4.30 Typical joints on a dual-lane divided carriageway.

Joints generally fall into two broad categories, viz tied and untied.

(a) Tied joints

The tiebars are designed to prevent separation of the joint faces;

separation of the faces would significantly reduce pavement life (see Section A4.1.2) and would allow incompressibles and water into the joint;

tiebars are not intended or designed to carry the shear load but only to hold the faces together so that load transfer can be achieved by mechanical interlock;

Longitudinal joints

Transverse contraction joints

Day’s pour

Mismatched joints Isolation joint

Transverse construction joints



58 Ed 2 / Rev 0

this “interlock” can be provided in a number of ways, such as by corrugations, keyways (no longer used in NSW) or by aggregate interlock;

tied joints are required to act as hinges in order to relieve curling and warping stresses which exist throughout the life of the pavement.

in the case of formed tied joints, positive action must be taken to debond the vertical face to prevent a chemical bond and to ensure that hinging does occur. This is best achieved by spraying the first-placed face with wax emulsion curing compound. Debonding was introduced in the early 1990s following significant problems with arris spalling on several new projects. (35)

(b) Untied joints

This category includes contraction joints, isolation joints, expansion joints and untied butt joints;

untied joints allow both hinging and joint separation. All untied joints must run continuous between free edges;

as with tied joints, positive action must be taken to debond the vertical faces because an intimate bond would lead to spalling in the second-placed concrete;

debonding is achieved by a filler (in the case of isolation and expansion joints) or by wax emulsion (in the case of butt joints).

Joint stresses

Joints are subjected to very high concentrated stresses, particularly at the arrisses. These stresses derive largely from movements associated with curling and live loading.

The capacity of a joint to sustain these stresses will largely depend on:

the concrete strength;

(Voided and/or under-compacted concrete is highly susceptible to failure. Inadequate curing can also have deleterious effect because arrisses are exposed to drying on two faces.)

the joint geometry;

(it is critical that the design details be carried into practice; see discussion below.)

freedom for the joint to hinge.

(Joints must hinge in order to relieve curling stresses, and any lock-up of the joint will merely transfer stresses elsewhere. The most common causes of lock-up are voiding in the first-placed face, and lack of debonding on the face.)

Joint treatment

At all joints, the vertical edge must be straight and square to the top surface. Rounding (tooling) of the first-placed edge is not allowed because it results in spalling of the mortar which fills the rounding during subsequent pours; Plate 4.31 shows an example. (Kerbs are an exception to this rule, but the radius of rounding must be limited; see Clause 4.6.)

35 If positive debonding is not achieved at the joint face, there is a high risk that the crack will form at an

offset of 20 mm to 50 mm into the second-placed slab.



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Plate 4.31 Spalling of mortar which has filled the rounding on the first-placed slab.

At formed joints, vertical faces are debonded to prevent intimate microtexture bonding which would prevent hinging. Debonding requirements are detailed in Clauses A4.5.1 and A4.5.4.1.

Defects in joint faces such as honeycombing and re-entrant angles will not be remedied merely by debonding and hence are unacceptable.

Corrugated joints

The corrugation geometry is critical to the functioning and durability of the joint. Plate 4.32.1 shows the current design detail for corrugated joints (both slipformed and fixed-formed).

Plate 4.32.2 shows the superseded detail which may still appear in older sets of drawings.

Plate 4.32.1 – Design details for corrugated joints.



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Plate 4.32.2 Superseded detail for corrugated joints.

Plate 4.32.3 A ready way to produce corrugated forms is to attach plastic quad to a standard timber formboard.

Plate 4.32 – Design of corrugated joints

Plate 4.33.1 An example of a very good slipformed corrugation. (Note, however, that current drawings reduce the number of corrugations and require a vertical section at the bottom.)

Plate 4.33.2 An example of a very good fixed-formed corrugation.

Plate 4.33 – Good corrugated joints

Below are examples of nonconforming corrugated joints.



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Plate 4.34.2 This is the mode of failure which will invariably result from the nonconformities shown left. In the example above, the top vertical face is only 15-20 mm instead of 50 5 mm.

Plate 4.34.1 This joint has two serious nonconformities: (a) the top corrugation is much closer than 50 mm to the top arris; (b) the top “vertical” is inclined at an angle (to the top surface) beyond the specified value of 840.

Plate 4.34 – Joint arrisses

Plate 4.35.1 This joint is clearly nonconforming. It would not readily hinge, and fracturing would inevitably occur along the vertical faces.

Plate 4.35.2 This joint will not readily hinge. Notwithstanding the application of a debonder, joint locking will occur which will lead to fracture along the face.

Plate 4.35 – Corrugated joints

4.5.2 Transverse Construction Joints

Transverse construction joints are required at the start and end of each paving run. They are typically located at mid-slab and are tied to ensure that contraction is restricted to the adjacent contraction joints.

Alternatively, a dowelled contraction joint may double as a construction joint but this will normally only be practicable in a dowelled pavement.

Transverse construction joints must .... be reinstated or repaired .... prior to the placement of adjoining concrete. The repair material must not be placed integrally with the adjoining concrete ....



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Plate 4.36 An example of a corner patch where the repair material has been placed integrally with the adjoining concrete and hence is nonconforming. The patch will dislodge within a short time, under the combined influence of traffic loads and curling strains.

4.5.3 Transverse Contraction Joints

Contraction joints must .... be maintained at all times free of incompressible and foreign materials, and sealed .... at all formed edges ....

The requirement to seal down the vertical faces was introduced after compression failures were observed in the early 1990s from the following series of events:

the mainline paving was undertaken during summer;

the shoulder paving was carried out during the next winter;

at that time, the contraction joints in the mainline were at their widest opening and so were exposed to ingress of mortar from the shoulder mix;

in the following summer, this mortar prevented closure of the joints and hence induced compression failures; see Plate 4.37. Its typical shape led to the adoption of the term “Y-cracking”.

The location of the cracking was indicative of the depth of penetration of the mortar. Fly ash mixes gave the highest penetrations because of their very good workability.

All examples of this cracking to date have involved contraction joints, but the same risk applies to all untied joints such as isolation and expansion joints (36).

36 Similar distress is known to have occurred on a few projects in the USA. [10]



Ed 2 / Rev 0 63

Sawcut

An example of compression cracking (left) resulting from mortar within the joint cavity, shown in the core above.

Plate 4.37 – Y-cracking

Sawn versus knifed joints

There are several methods available to induce contraction joints, including sawcutting and knifing (also known as “guillotined”). The standard method under R83 is sawcutting, and knifing is only allowed in limited areas where shown on the Drawings. Its use is restricted because:

it produces a noticeably rougher ride; and

there is an increased risk of arris failure if the concrete isn’t thoroughly re-compacted around the inducer.

For these reasons, knifing is usually only suitable for untrafficked or low-speed areas.

4.5.4 Expansion Joints

Expansion joints must .... be treated with joint filler, complying with RMS 3204, and joint sealant ....

It is important that the filler be placed such that it totally covers the full joint face. If concrete is allowed to bridge the cavity (even within a small area) it will exert high concentrated compressive stresses in hot conditions. Distress of the type described in Section 4.5.2 would be likely.

4.5.5 Longitudinal Joints

Note that longitudinal joints will typically terminate at tied transverse construction joints. It is structurally unacceptable to use a formed and scabbled transverse construction joint.



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Plate 4.38 Longitudinal joints will typically terminate at transverse tied construction joints. (There are very few alternatives, but one is to terminate at an isolation joint.) Longitudinal joints cannot terminate at contraction joints because: (a) it is impossible to terminate a pour at a sawn joint,

and (b) it is structurally unacceptable to create a formed &

scabbled transverse construction joint. ( indicates mesh reinforcement)

See further comments in Section 4.5.

4.5.6 Isolation Joints

See comments in Sections 4.5 and 4.5.3.

4.5.7 Mismatched Joints

Mismatched joints present a risk for the following reasons:

there is a risk of unplanned reflection cracking;

moving joints (like contraction joints) may be locked up by the adjoining slab.

Hence, mismatching should always be treated with caution.

Tied joints (such as transverse construction joints) present very little risk but untied joints (such as contraction joints) must never be allowed to form mismatched joints, except across isolation joints; see Plates 4.39 and 4.40.

Plate 4.39 Experience to date is that tied construction joints do not cause reflection cracking.



Ed 2 / Rev 0 65

Contraction joints will reflect across butt joints (whether tied or not)

Joint reflection will not occur across isolation joints

Plate 4.40 – Refection cracking at mismatched joints

Plate 4.41 Mismatching of transverse contraction joints at a longitudinal tied joint.

4.5.8 Outer Edges

Outer edges must .... have .... corrugations and tiebars only if and as specified on the Drawings.

Corrugations are provided to cater for future possible pavement widening.

There is a common tendency to relax the specified criteria at outer edges because of the attitude: “what does it matter at the outer edge?”

This attitude must be discouraged because the intent of the specification is to provide an edge which is suitable for future widening should the need arise (for extra lanes, shoulder widenings, median crossings etc).

Recent cases have been encountered (of pavements constructed in the 1980s) where substantial and costly remedial treatment has been needed prior to widening in order to correct edge problems. Defects can include:

edge slump, sometimes reaching up to 0.3 m from the edge;

voided (honeycombed) concrete;

arris spalling;

significant deviations in alignment.



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See also comments in Section 4.5.

Plate 4.42 A slipformed edge showing only minimal edge slump.

4.6 KERB AND GUTTER

Fixtures such as kerbs and islands must be structurally compatible with the adjoining base, hence:

base joints must be extended into the adjoining kerb in like type, and

the same applies to overlying islands and medians.

Adjacent to concrete pavements, a substantial kerb can be considered to provide “shoulder widening” under the terms of the Austroads Guide and Form 76. A “without shoulder” design is likely to be 30-40 mm thicker (37). Stiffness calculations show that a Type SA kerb (for example) provides equivalent edge stiffening to a tied shoulder of about 1.7 m width.

However, in order to fulfil this function, the kerb must be effectively tied to the adjoining base. In order to provide long-term structural support, the tiebars must be durable and soundly bonded.

Extruded kerbs are not considered to provide effective edge stiffening because:

the strength can be highly variable (due to poor and variable compaction), and

tiebar pull-out strengths are very unreliable in extruded kerb mix.

Similarly, different kerbs will provide differing levels of support.

type SA kerb is considered to provide the full required structural support;

type SE kerb is unlikely to do so;

type SF kerbs will definitely not provide edge stiffening and hence the base is typically extended by a minimum of 0.5 m behind the face of kerb.

Mountable kerbs (such as SF) must be secured against displacement when struck or mounted by trucks and hence are tied to the base. These ties have to be low enough to enable the passage of an extruder, hence the specified protrusion of 35 10 mm above the base surface. Cases are known where these ties have been hammered flat with the surface; this is obviously unacceptable.

Joint design adjacent to islands and medians warrants close attention to ensure that small portions of kerb will not be separated when the base joints are extended into the kerb. Median noses are the areas of greatest risk. The angle of intersection between the joint and the kerb should also be checked to

37 Note that edge stiffening will only be a critical structural issue where significant volumes of commercial

vehicles are likely to track close to the kerb.



Ed 2 / Rev 0 67

minimise the risks of kerb spalling at acute angles. Joints which are located directly under, and parallel with, overlying kerbs (such as type SF) will induce cracking and spalling in the kerb within days of its placement.

Plate 4.43.1 At design stage, kerb/joint interaction requires attention. At construction stage, a minor realignment of the kerb may be required.

Plate 4.43.2 Untied kerbs can become a hazard, particularly after they break into short lengths.

Plate 4.43.3 The drawings require that at least one tiebar be provided in any discrete section of kerb or nosing.

Plate 4.43 – Type SF kerbs

Plate 4.44.1 Reflection cracking in a Type F barrier. Similar cracking could also occur longitudinally if the barrier were placed over a longitudinal joint (regardless of whether that joint is tied or untied).

Plate 4.44.2 Reflection cracking in a median island.

Plate 4.44 – Reflection cracking



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4.7 SPECIAL SLABS

4.7.1 Odd-shaped and Mismatched Slabs

Slabs are most structurally stable when they are approximately square shaped.

As the length-width ratio increases, there is an increased risk that the slab will break into two approximately square slabs.

Also, as corner angles become more acute, there is increased risk of corner cracking. The influence of corner angle is indicated in Plate 4.45.

Plate 4.45 The influence of corner angle on slab stress.

RMS current slab dimensional limits are as tabulated in Plate 4.46.



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Plate 4.46 – Slab dimensional limits

PCP PCP-R JRCP SFCP (ii)

Trafficked slabs

Minimum corner angles (vi) 84 84 84 80 (70)

Slab length L (iii) (m)

Lmax Lmin

4.2 3.4

4.2 3.0

10.0 (12.0) 3.5 (iv)

6.0 2.5 (v)

Slab widths W (iii) (m)

Wmax Wmin

4.3 (4.4) Lact/Rmax

4.3 (4.5) 1.0

4.3 (4.5) 1.0

4.5 (5.0) 1.0

Shape factor R (LW)

Rmax Rmin

1.25 0.8

4.2 0.67

10 0.8

6.0 0.6

Untrafficked slabs

Minimum corner angles6 84 (80) 80 (75) 80 (75) 70 (65)

Slab length L (iii) (m)

Lmax Lmin

4.4 Wact x Rmin

4.4 2.5

10.0 (12.0) 3.5 (iv)

6.0 (6.5) 2.5 (v)

Slab widths W (iii) (m)

Wmax Wmin

4.4 (4.5) Lact/Rmax

4.4 (4.6) 0.6

4.4 (4.6) 0.6

4.7 (5.0) 0.3

Shape factor R (LW)

Rmax Rmin

3.0 0.7

7 0.55

16 0.8

22 0.5

Notes (i) Dimensions in brackets show acceptable “relaxed” criteria for use where alternatives are

not available. (ii) For full design guidelines for SFCP, refer to the RMS Roundabout Design Guide [4]. (iii) Length is measured between transverse contraction joints. Width is measured between

longitudinal joints. The subscript “act” refers to “actual” dimension. (iv) In structural terms, JRCP slab lengths as low as approx 3.5 m are acceptable but from

practical and economic considerations they should rarely be lower than about 7 m. (v) The lower limit in SFCP is specified with the aim of minimising the uneven induction of

joints. Slab lengths of 5-6 m are preferred and the use of lower values should be limited to the inside of curves.

(vi) Acute corner angles increase the slab stresses substantially. This also applies to untrafficked slabs because of the effect of curling stresses. Hence, angles should be maximised wherever possible. Bracketed values should be used with care.



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4.7.2 Anchor Slabs

and

4.8 Slab anchors

anchor slab

slab anchor

ZZ

construction joint

(reinforcement not shown)

Plate 4.47 – Anchor terminology

the anchor slab is the part above the horizontal joint

the slab anchor is the stem below the joint.

Anchors are provided to arrest longitudinal growth of the pavement, hence protecting any abutting structures and flexible pavements against horizontal thrust.

They also play an important role in maintaining small openings in the adjacent transverse joints. This serves to maintain aggregate interlock and to minimise sealant stresses.

These issues are important in both dowelled and undowelled pavements, with the exception that aggregate interlock is unimportant in dowelled pavements.

.... anchor stirrups must be lapped (as defined) to the base reinforcement, which must not have other laps within 1.3 m of the anchor axis ....

Note that “lapped” is different to “tied”. See Definitions in Annexure R83/5.

5 END PRODUCT CRITERIA

5.1 CONCRETE CRACKING

(a) Crack classifications

A clear distinction must be made between different cracking types. In the context of structural distress, it is feasible to classify cracks according to either their impact or their behaviour, as follows:

impact: e.g. “structural” or “surface”

behaviour: e.g. “moving” or “static”.

Full structural cracks move constantly under the effects of traffic and curling.

By contrast, short plastic shrinkage cracks are typically static. However, there have been cases where a series of plastic shrinkage cracks have slowly joined up over several years (of trafficking and curling) to form full structural cracks.

Another typical point of distinction between the two types is their point of initiation, as follows:

plastic shrinkage cracks are invariably “internal” and they very rarely intercept a slab edge or a formed joint;



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(Interception of an induced joint is an exception, because the plastic cracking invariably occurs before the joint induction. A further rare exception is discussed below under the title “edge cracking”.)

structural cracks either initiate from an edge or quickly grow to intercept an edge (or joint).

Classification of some crack patterns can be difficult in the early days after initiation. Given that many structural cracks begin from a point source and then progress across the slab, they do not technically become structural cracks until they have progressed far enough to allow significant movement (such as rotation). This could take days, weeks, or even months. Whatever the duration, if they are physically growing then this clearly distinguishes them from short plastic shrinkage cracks which are typically dormant (at least within the short-term).

Hence, for most purposes, a crack can be deemed to be structural if it is growing. This “growing” will invariably be lengthwise but it could also involve deepening.

(b) Specification criteria

For simplicity, the specification uses only three classifications, viz “plastic shrinkage”, “drying shrinkage”, and “other”.

In this context, the term “drying cracking” is used to cover the cracking which can be expected to occur in well designed and constructed pavements. In reality, such cracking is not due only to drying but occurs under the influence of contraction and/or curling, and these result from temperature and/or moisture variations.

Plate 5.1 indicates the types of cracking which are classified under the specification. Any cracking not shown here would be deemed “other”.

Plastic shrinkage cracking

Plate 5.1.1: Plain Concrete Pavement (PCP) and Steel-Fibre Reinforced Concrete Pavement (SFCP) The only tolerable cracking (apart from induced joints) is plastic shrinkage cracking, within specified limits.

Dryingshrinkagecracks

Dowelled contraction jointsPlastic shrinkage cracking

Dryingshrinkage crack

Plate 5.1.2: Jointed Reinforced Concrete Pavement (JRCP) and Reinforced PCP (PCP-R) JRCP slabs of length greater than about 5.5 m or with length/width ratio greater than about 1.5 are likely to form transverse hinge joints which will result in “squarer” slabs (38). Under the specified construction conditions (39), these

38 In other words, for widths of about 4 m, slabs of 8 m length (between contraction joints) will typically

crack into two 4 m lengths, and 12 m slabs will typically crack into three 4 m lengths.



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cracks will be discrete, full depth and full width (of that slab). They will be aligned at right angles to the longitudinal joints, 50 approx. Under good construction conditions, they will not occur closer than about 3 m from a transverse joint unless the slab width is less than about 3 m (40). These cracks do not constitute “unplanned cracking”. Plastic shrinkage cracking is also acceptable, within specified limits. The use of PCP-R is typically required where unusual stresses are likely to exist which could cause drying shrinkage cracking. Such cracking should typically accord with the guidelines for JRCP.

Drying shrinkage cracks

Plastic shrinkage cracking

Plate 5.1.3: Continuously Reinforced Concrete Pavement (CRCP) Under the specified construction conditions (39), these cracks will be discrete, full depth and full width (of that slab). They will be aligned at right angles to the longitudinal joints ( 50 approx). These cracks do not constitute “unplanned cracking”. Plastic shrinkage cracking is also acceptable, within specified limits.

Plate 5.1 – Cracking types

(c) Plastic shrinkage cracking

Plastic cracking is sometimes sub-divided into two separate types, viz:

plastic shrinkage cracking, and;

pre-setting cracking.

“Plastic shrinkage cracking” is typically caused by rapid evaporation of the mix water, and can be exacerbated by thermal stresses.

“Pre-setting cracking” is typically caused by differential plastic settlement (possibly resulting from the loss of bleed water) and is related to external restraints such as reinforcing bars or formwork.

However, from a contractual sense, this distinction is unnecessary because they are equally (potentially) damaging to the finished concrete, they become evident within similar time-frames (i.e. in the plastic state), they result from similar factors, and they can be avoided by careful application of good construction practice. Hence, under this specification, they are grouped as “plastic shrinkage cracking”.

Plastic cracking often occurs as soon as one hour after placement and often as soon as 30 minutes after placement.

In plain (unreinforced) concrete, plastic shrinkage cracks are often less than 30 cm long and will typically exhibit random orientation. Under the influence of traffic loading, they can develop into full structural cracks.

39 This includes issues such as conforming debonding treatments etc. 40 For slab width W, hinge cracks should not occur less than about 0.8W from a transverse joint. Cracks

closer than this should be investigated, and possible causes include late sawcutting and lock-up of dowels.



Ed 2 / Rev 0 73

Plastic shrinkage is often accompanied by the simultaneous occurrence of plastic settlement (resulting from the loss of bleed water) and, in reinforced concrete, this cracking may reflect the location of underlying reinforcement and can lead to its early corrosion.

Once cracking has occurred, revibration appears to be the only satisfactory and effective “plastic” treatment. Revibration of concrete offers many benefits and few (if any) drawbacks. Surface revibration is usually more practical and effective than internal revibration.

Static (non-vibratory) floating is rarely effective in closing plastic shrinkage cracks to any significant depth and in most cases they will reappear after further drying. Also, ill-timed or prolonged finishing and floating operations can produce surplus slurry which may exacerbate the cracking potential.

In assessing the acceptability of plastic shrinkage cracking, the key issue is the extent to which the cracking is likely to compromise the flexural fatigue life of the slab. In reinforced slabs, the issue of potential steel corrosion also needs to be considered.

If the cracking is minor and is not located within a critical stress section then its presence is unlikely to cause any significant loss of slab sectional area, which explains why the specification tolerates a low level of such cracking.

However, if there is significant cracking through any particular slab section then it will act in exactly the same way as a sawcut to induce crack growth (under fatigue loading) and this will eventually lead to full structural cracking. Under this model, the width of cracking is irrelevant, hence even “hairline” cracks will compromise the fatigue capacity. This has been observed on past projects.

In the case of SFRC, the steel fibres which are located at the extremities of the cracks (i.e. the ends and bottom) could be exposed to corrosion and hence won’t necessarily serve to arrest crack growth in the longer term.

In the case of significant cracking, sealing of the cracks may be effective in reducing steel corrosion but will not be effective in arresting growth.

Many variations of crack “glueing” (such as epoxy injection) have been tried over the past 20 years, but none has been effective in arresting significant cracking. The only cases which might be considered to have been effective are those where the cracking was so minor that crack growth would have been unlikely even without the treatment.

(d) Edge cracking

On several projects a form of plastic shrinkage edge cracking has occurred at the top edge on the western side of the slab on the high side of the crossfall. It is considered to have occurred through a combination of migration of moisture (to the downhill side) and the effects of the afternoon setting sun. Ongoing recurrences appeared to be prevented by application of additional curing compound.

5.2 CONCRETE COMPACTION



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Plate 5.2.1 Uncompacted concrete at a transverse (corrugated) construction joint in PCP (under a median kerb nosing).

Plate 5.2.2 Poorly compacted concrete at a transverse construction joint in CRCP.

Plate 5.2 – Nonconforming compaction

Compaction has a significant influence on several important properties such as strength and permeability, and hence on durability. Neville [20] states that “full compaction is more important than a low water/cement ratio coupled with a poorly compacted concrete”.

However, on typical civil construction sites, compaction receives too little attention and, very often, specifications for major engineering projects do not require its testing or assessment. Srinivasan [21] states: “there has been repeated criticism of poor construction practices, especially regarding compaction and curing. These criticisms are not confined to any nation or .... any category of builders. It is universal, and applies .... to every category of contractors.”

“In Swedish bridge construction, several cases were reported in the 1980’s where insufficient consolidation resulted in serious defects, necessitating .... in one case, total demolition and reconstruction.” (Forssblad [22])

In summary, under-compaction is a regular problem throughout the construction world and therefore warrants closer attention than it typically receives [19].

For pavements, it requires an even higher priority. Pavements are relatively more sensitive to variable quality because of the probing nature of truck loading (which, in time, will find every weak slab) combined with the fact that pavements perform in flexural fatigue which is very sensitive to under-compaction.

For example, there is substantial research which shows that 1% of air voids theoretically causes:

a 6% reduction in compressive strength, and;

a 4% to 5% reduction in flexural strength.

Plate 5.3 shows the relationship between concrete strength and design fatigue life (i.e. ignoring erosion

(41)) for a range of cement contents. It also shows that:

for a typical 300 kg paving mix, 2% additional voids will reduce a 35 MPa strength to 31 MPa, and 3% voids will reduce it to 27 MPa.

Under-compaction by 2% has the same impact on flexural strength as a cement reduction of 30 kg/m3.

41 Under the Austroads design model, the two design criteria are fatigue and erosion. The design of PCP is

typically dominated by erosion, but CRCP and JRCP are dominated by fatigue.



Ed 2 / Rev 0 75

In the general construction industry (where the testing of compaction is rare), void contents of 4 to 5% are common. Such levels are sometimes also encountered on RMS projects when paving operations are less well controlled. Plate 5.3 shows that in situations where compaction will be marginal (or untested) a high safety margin is warranted on strength (and hence also on cement content).

Plate 5.3 – The effect of void content on strength for various cement contents

Plate 5.4 indicates the influence of density and strength on the design fatigue life for a range of Base thicknesses (42).

(The x-axes have been compiled by using the relationship of 1% voids causing a 6% strength loss. For example, a specific mix which yields 36.0 MPa UCS at 100% relative density (i.e. the right-hand extremity of the axes) could be expected at 98% density to yield a UCS of about 31.7 MPa and a flexural strength of about 4.1 MPa. This reduced flexural strength has been used as input to the thickness design process.)

Two separate Case Studies are marked for demonstration purposes, as follows:

Study No 1 (green) indicates that a reduction in density to 97% would reduce the strength from 36.0 to 29.5 MPa. In order to compensate, the Base thickness would have to be increased from 200 mm to 230 mm.

Study No 2 (red) indicates that for the same mix, a relative density of 98.5% will reduce the strength to about 33.0 MPa, in which case a thickness of 210 mm will yield a design life of about 38 years. If the relative density then drops to 97.5%, the design life for that 210 mm slab will drop from 38 years to about 17 years.

42 The design charts are for CRCP based on the following parameters: LSF = 1.3, 40-year traffic = 3.0 x 108 HVAGs, growth rate = 4.5 %, effective CBR50.



76 Ed 2 / Rev 0

190 mm

240

mm

200

mm

210

mm

220

mm

230

mm

250

mm

Compressive (MPa)

Flexural (MPa)

Relative density (RD)%

25.0 27.5 29.5 31.7 34.0 36.0

95 96 97 98 99 100

3% RD = 30 mm thickness

(red

)

(gre

en)

(gre

en)

(red

)

Plate 5.4 – Influence of strength & density on pavement fatigue life

Note that the above measures of compaction and voids are “relative” measures. It is difficult to define these properties in absolute terms because:

(a) “full” absolute compaction is an unrealistic target because the removal of all air is not possible even after vibration durations beyond one hour;

(b) each mix has a different theoretical maximum unit mass depending on its composition and constituents.

Under R83, assessment is made on the basis of the unit mass of cores relative to the unit mass of standard reference cylinders, with criteria as per Plate 5.5.

Plate 5.5 R83 Compaction criteria

* R & R = remove & replace

The reference cylinder value is based on a rolling mean of 5 pairs, in order to minimise the impact of short-term fluctuations in properties such as entrained air content. This is termed the “rolling cylinder unit mass”, or RCUM; see Plate 5.6.

97%

100%

Conforming

Conforming if 28-day core strength conforms, otherwise R & R *

98%

Relative Density

Non-conforming, R & R *



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Plate 5.6 Derivation of rolling cylinder unit mass (RCUM).

RCUM

Cylinder resultsat 7 days

Density from coreat 3 to 7 days

Results from a lot

Results at various consecutive lots

Density(kg/m3)

When using “relative” assessment criteria, it is critical that the degree of compaction in the reference cylinders be reliable and repeatable. To this end, all specimens must be moulded in accordance with Test Method T304, which differs from AS1012.8 in the following ways:

(a) Cylinder compaction must be by internal vibration. Hence, rodding and external vibration are not allowed. (Exceptions exist for SFRC.)

(b) Flexure beam compaction is more closely specified than under AS1012.

(c) Internal vibrators must be electrical. Petrol vibrators are excluded because they can be throttled to give a wide range of frequencies, which has a marked impact on variability.

(d) Vibrators must have a minimum frequency of 115 Hz (6900 v/min), consistent with AS 1012.8.

T304 imposes an upper limit of 220 Hz (13,200 v/min) in an effort to avoid cavitation.

(e) Minimum vibrator insertion times are specified. The concrete must be placed in two layers (consistent with AS 10102.8) and there must be two vibrator insertions per layer.

The enforcement of T304 has resulted in a substantial reduction in standard deviation in both the unit mass and the strength of cylinders (43).

More importantly, core unit masses have also been significantly reduced.

AS1012 allows various specimen sizes but R83 nominates particular sizes. However, for any particular size, T304 adopts the dimensions specified by AS1012.

For contract purposes, the RCUM (when derived in accordance with T304) is effectively deemed to constitute “full” compaction.

43 This suggests that, in the general construction industry, unnecessarily high variability in moulding

procedures could be giving misleading information on the standard of concrete production control.



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Plate 5.7 Test T304 seeks to minimise variability in cylinder compaction.

5.2.1 Conformity for Compaction

Transition Zones must be treated as separate lots of work .... .... at each transverse construction joint in slipformed work, two discrete transition zones will occur ....

The relationship between Lots and Sub-lots at transition zones is shown diagrammatically in Plate A5.1.

Transition zones were introduced to address the high incidence of failure adjacent to transverse construction joints in slipformed work, particularly in CRCP.

As an example, in two contracts completed during the 1990s (totalling about 11 kms of dual carriageway), every individual construction joint has been replaced as a result of failure within eight years of construction.

Transitions can also occur in the middle of a paving run if, for example, the paver’s progress is significantly interrupted (without the need for a construction joint) in such a way that doubt exists about the thoroughness of compaction within that zone.

In the case of construction joints, both the “start” and “finish” transitions must be regularly checked. They are constructed by different operations and each has its own typical problems, as follows:

Finish joints:

(a) are typically constructed by paving beyond the planned joint location, after which the excess mix is removed to allow placement of the header board;

(b) throughout the day’s paving, slurry builds up in the paver’s vibrator box (also referred to as a “slurry box”) and care is required to ensure that all of this slurry is removed and that pockets do not remain within the transition zone.

(c) after placement of the header board, it is important that the transition zone be fully revibrated with internal vibrators, and possibly also with surface vibration;

(d) given that this involves a low-slump machine mix, the vibration needs to be even more thorough than that required in typical fixed-form work.

Start joints:

(e) typically require the paver to be reversed against the previous pour;



Ed 2 / Rev 0 79

(f) the position of the paver will typically be such that the vibrators will not impact on the first few metres of the pour, and so this complete area must be vibrated by hand;

(g) again, this involves a machine mix and so the vibration must be very thorough.

Plate 5.8.1 shows a typical failure adjacent to a transverse construction joint. In this case, the photograph shows failure in CRCP, and it is known to be in the morning “start-up” transition.

Note that the failure is about 2 m from the joint and is indicative of the area which is not compacted by the vibrators on the slipformer. In other words, manual vibration must cover the full area which has not been compacted by the paver.

Under Clause A4.3.3, the contractor is required to nominate this length for his specific paver(s).

Manual compaction which is limited to the immediate joint edge (as shown in Plate 5.8.2) is likely to leave a large area of uncompacted slab.

Plate 5.8.1 Transition zones extend for 3 m each side of a transverse construction joint.

Plate 5.8.2 Manual vibration must extend beyond the immediate joint edge to cover the full zone which has not been compacted by the paver.

Plate 5.8 – Vibration in transition zones

Note also that, even though Clause 5.2.1 defines the transition zone as 3 m in length, the contractor is obliged(44) to compact the full pavement area. Hence, if the slipformer leaves 5 m of uncompacted slab adjacent to the joint then manual vibration must cover this whole area.

Longitudinal formed joints are another possible location of under-compaction which should be checked. Plate 5.9 shows an example of a paving run against an existing slab.

44 This obligation is covered by various clauses, including the Quality System documents.



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Plate 5.9.2 Voids exposed by slitting the core in Plate 5.9.1

Plate 5.9.1 Under-compaction exposed by coring through a longitudinal formed joint (which was later sawn to provide a sealant reservoir).

Plate 5.9 – Vibration against an existing longitudinal edge

Another area of risk is the zone above tiebars which have been injected through the top surface of slipformed slabs. Refer to Section A4.1.2(ii) for further discussion.

5.3 CONCRETE COMPRESSIVE STRENGTH

5.3.3 Core Strength Testing

Under the terms of the specification, core strength testing is initiated via a compaction nonconformity, but not via a nonconformity in cylinder strength.

However, where cylinder strengths are low and there is reason to believe that it could be related to moulding and/or testing procedures rather than concrete quality, the Principal could consider, solely at his discretion, the warrant for a limited program of core testing.

5.3.4 Conformity for Compressive Strength

5.3.4.1 Test Cylinders

Concrete with a .... (low) .... 28-day cylinder strength .... will be subject to a deduction of 4% .... for each 0.5 MPa .... deficiency in strength.

This may seem like an inflated deduction, but it is closely related to the real life-cycle impact of low strengths.

Plate 5.10 provides an indicative relationship between strength and fatigue life for a CRCP design(45) (in which erosion has no influence (41)). The Austroads model shows that a reduction in compressive strength from 36 MPa to about 31.5 MPa will effectively halve the fatigue life.

45 The Austroads design in this example is based on the following parameters:

Effective CBR50, 40-year design traffic 2.3 x 108 cvag, Load safety factor = 1.2. Resulting CRCP thickness = 200 mm (without tolerances).



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Plate 5.10 – The influence of concrete strength on pavement fatigue life (45)

5.3.4.2 Cores

A lot .... will conform .... if the corrected strength is greater than or equal to fcMin for all core specimens from that lot.

Note that conformity is not based solely on the mean of the results but also on individual results; see discussion in Section A5.3.3.

Note also that core strength testing is only initiated via a compaction nonconformity; see comments under Section 5.3.3.

5.4 GEOMETRY AND THICKNESS

5.4.2 Level Survey

The level at any point on the top of the base must not vary by more than 20 mm above or 0 mm below the design level (+20, -0 mm).

Close tolerances are required because of issues such as the risks associated with ponding of water on the carriageway, particularly at superelevation transitions.

5.4.3 Thickness Assessment

Minor deficiencies in thickness have a substantial impact on rigid pavement life, as shown in Plate 5.11. Deductions are consistent with this life reduction.

The significant difference between the two curves appears to be related to their assumed load-damage

relationships. The AASHTO model is based on the 4th power law which is now thought to be far too low for rigid pavements. The PCA/Austroads model is based on a power of about 18, and gives results which are more consistent with observed performance.



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Plate 5.11 – The influence of thickness deficiency on fatigue life

5.4.4 Conformity for Thickness

Each lot must be assessed on the basis of mean thickness and individual deficiencies. The result is then classified into one of the row categories in Table R83.12 (of R83).

The following is an example of the application of this table.

Thickness deficiency

Individual Text

Reference Mean (mm) Result

(mm) Frequency

Status/Action

5 > 2

and/or Nonconforming,

Nonconformity Nil and 10 to 15 1 45% deduction

and

20 Nil

Application:

If: the mean deficiency is NIL and there are no deficiencies of 20 mm or

more,

and

there are more than 2 individual deficiencies of 5 mm,

and/or there are 1 or more individual

deficiencies of 10 to 15 mm,

.... then a 45% deduction will apply.

An example is provided in Plate 5.12 for a project with a specified thickness of 245 mm.



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Note that rounding must be in accordance with AS2706. For rounding to the nearest 5 mm:

1 and 2 round down to 0,

3, 4, 6 and 7 round to 5, and

8 and 9 round up to 0.

Plate 5.12 – Application of thickness criteria

Thickness Readings (mm) (i)

Readings Lot 452 Lot 562 Lot 579 Lot 582

R1 249 (250) 247 (245) 230 (230) 250 (250)

R2 241 (240) 245 (245) 232 (230) 245 (245)

R3 244 (245) 244 (245) 234 (235) 240 (240)

R4 241 (240) 246 (245) 236 (235) 240 (240)

R5 245 (245) 245 (245) 245 (245) 258 (260)

R6 248 (250) 245 (245) 248 (250) 240 (240)

R7 250 (250) 250 (250) 250 (250) 230 (230)

R8 261 (260) 225 (225) 261 (260) 246 (245)

Calculations (The specified base thickness = 245 mm)

Mean of 8 readings (ii) 247 243 242 244

Rounded mean 245 245 240 245

Mean Deficiency 0 0 -5 0

Freq: 5 mm deficient (iii) 2 0 0 3




Status / Action Conforming R & R (iv) 24% deduct. 45% deduct

Notes (i) Bracketed values have been rounded to the nearest 5 mm. (ii) The mean is calculated using exact thickness (prior to rounding). (iii) Deficiency frequencies are based on rounded values. (iv) R&R = Remove & replace

5.5 SURFACE PROFILE

5.5.2 Longitudinal Profile

The requirements of the longitudinal profile testing regime are as follows:

(a) the straight-edge criteria applies to all locations.

(b) the ARRB-TR Walking Profiler (ARRB-WP, or WP; see Plate 5.13) must be used to test the following specific areas to identify localised areas which warrant grinding:



84 Ed 2 / Rev 0

transverse construction joints;

at approach sections where roughness testing will not be possible;

at all slab replacements.

(c) after the completion of any mandatory grinding under (a) and (b), roughness is assessed (using a roughness car);

(d) an incentive or deduction is applied to roughness results;

(e) the contractor may undertake additional grinding in order to reduce deductions and to increase incentive payments;

(f) areas which cannot be assessed for roughness (due to inaccessibility, for example) are assessed for profile index using WP results.

The straight-edge criteria apply to the whole project but there is no stipulation on the frequency of testing and, in practice, it is likely to vary from one project to another.

It is possible, for example, that a pavement length could satisfy both WP and roughness criteria but still contain isolated deviations outside the areas tested under category (b) which would be deemed unacceptable by a majority of motorists. The straight-edge criteria must be applied to these locations.

In addition to mandatory testing, contractors are encouraged to use the WP in order to improve the ride quality of their projects through the use of early feedback. Because of both trafficking restrictions and logistics, roughness testing will rarely be possible until several weeks after paving a particular lot. Roughness results obtained at that time will be of very little benefit because most memories will have faded of events which caused the rough areas. Additionally, those same faults may have been repeated on subsequent work, possibly involving many kilometres of pavement.

By contrast, the ARRB-WP can be used on the day after paving and will therefore provide early and useful feedback to the paving crew. The WP provides an absolute surface profile (reduced level) at spacings of about 232 mm and so the output clearly identifies specific surface irregularities, which roughness testing cannot do.

The method used under R83 to assess the results is adapted from the American procedure which uses the California Profilograph (CP). However, the WP provides the following advantages over the CP:

it is substantially smaller and lighter, and more readily transportable;

it provides real surface profiles whereas the CP is effectively a rolling straight-edge which provides deviations relative to the wheel supports.



Ed 2 / Rev 0 85

Plate 5.13 The ARRB-TR Walking Profiler (WP)



86 Ed 2 / Rev 0

BACKGROUND NOTES

Surface profiles

Clause 5.5 deals only with surface profiles which fit within the wavelength band which is defined as “roughness”. There are three other profile categories as listed in Plate 5.14. These bands have been selected (by PIARC(46)) according to the impact on the tyre and the vehicle suspension, as shown.

In brief, only the roughness wavelength has an impact on NAASRA roughness measurements. In other words, megatexture appears to have no influence on roughness results.

Plate 5.14 – Surface Profiles

Category Wavelengths () Examples Impact

Microtexture 0.5 mm Sand texture tyres only

0.5 mm 50 mm tining (in concrete)

coarse aggregate (in sprayed seals)

tyres only

50 mm 500 mm settlement over steel (in concrete)

stripped aggregate (in sprayed seals)

tyres only

0.5 m 50 m Long wavelength deviations

suspension and tyres

R83 specifies requirements for each category except megatexture which, at this stage, cannot be adequately quantified and measured. Notwithstanding, it causes significant discomfort to motorists and so every effort should be made to minimise it.

Examples of megatexture are shown in Plate 5.15. It is rarely visible in full daylight. It is most easily detected under headlights and can also be detected during low light at sunrise and sunset.

Plate 5.15.1 Megatexture in CRCP, indicating transverse reinforcement (Y12 bars @ 500 c/c)

Plate 5.15.2 Megatexture in JRCP, indicating transverse wires in reinforcing mesh (F82)

Plate 5.15 – Examples of megatexture in concrete pavements

END OF BACKGROUND NOTES

46 Permanent International Association of Road Congresses, now called the World Road Association.



Ed 2 / Rev 0 87

5.6 REMOVAL AND REPLACEMENT OF CONCRETE BASE

In identifying the limits of any removal and replacement (R&R), consideration should be given to its likely impact on the structural integrity of the final product. In extreme cases of piecemeal (or patchwork) removal, the pavement life is likely to be compromised, though this will depend also on factors such as the quality of the reinstatement work.

An example of undesirable patchwork removal is shown in Plate 5.16.

This should not be taken as reason to avoid R&R when it is warranted, but rather to advocate that:

(a) In cases where a substantial proportion of any discrete area of pavement is nonconforming, the whole area should be removed and replaced in order to maximise structural continuity. This applies especially to CRCP, but also to other formats such as PCP. Precedence for this principle has been established in past RMS litigation cases.

(b) The standard of workmanship in the replacement work needs to be of a very high standard if it is to provide reasonable service. There is ample experience to show that repairs can be completed to a high standard which will give good performance for long periods under intense traffic loading.

Plate 5.16 Piecemeal/patchwork removal of Base is likely to compromise the long-term performance of the pavement.

5.6.2 Removal and Disposal of Base

The base must be removed at transverse construction joints which are ....

.... not closer than 1.5 m to an existing contraction joint in the base.



88 Ed 2 / Rev 0

Plate 5.17.1 Formed & scabbled transverse construction joint are inferior to tied joints and hence are not permitted in new works.

Plate 5.17.2 Transverse construction joints in PCP must be located “within-slab” and be tied.

Plate 5.17.3 Dowelled contraction joints may be used as an alternative form of construction joint.

Plate 5.17 – Construction joints in PCP (for slab replacement)

Plate 5.17.1 shows the removal and replacement (R&R) of a slab between transverse contraction joints. American experience indicates that construction joints of this type will not provide the same degree of load transfer as the original induced joint and therefore they are not permitted under R83.

Plate 5.17.2 shows the specified method of forming construction joints for R&R operations. The joint must be “within-slab” and not closer than 1.5 m to a contraction joint.

Plate 5.17.3 shows an acceptable alternative, but this would rarely be more efficient. Where used, they must be located at the position of the original contraction joint so that mismatched joints are not created.

5.6.3 Replacement of Base

Further guidelines are available in RMS’s “Guide to the Maintenance of Concrete Pavements” [5].

5.7 RECTIFICATION OF FINISHED SURFACE AND RIDE QUALITY

Areas requiring grinding must be rectified with purpose-built equipment employing gang-mounted diamond saw blades .... Impact methods such as rotomilling must not be used.

Grinding/profiling is a process undertaken with purpose-built equipment which uses diamond saw blades which are gang-mounted on a cutting head. There are typically 150 to 200 blades per metre wide cutting head. The spacing can be varied to suit the hardness of the aggregate in the concrete.

Grinding/profiling is a cutting process that creates a fine “corduroy” surface texture which is quiet and smooth, and which gives very good friction values. The process is routinely used overseas to achieve one or more of these outcomes. It is typically done longitudinally.

Grinding should not be confused with grooving or rotomilling.

Grooving comprises sawcuts at typical spacings of 10 to 18 mm.



Ed 2 / Rev 0 89

Grooving is typically done transversely (possibly after grinding) in order to restore waterpaths for wet weather friction. Care is required in the design and use of grooving because it often generates high frequency tyre noise.

Rotomilling is an impact or chipping process.

Rotomilling is not an acceptable alternative to grinding and must not be used on exposed concrete pavements (i.e. without an asphalt surfacing). It causes unacceptable damage to joints, as shown in Plate 5.18.2, which will generate an ongoing maintenance demand. It is also likely to create an unpleasant noise level and (harsh) ride quality.

Plate 5.18.1 A surface after longitudinal grinding and transverse grooving. (The ground area appears as a matt finish.)

Plate 5.18.2 Joint damage and harsh surface texture caused by rotomilling.

Plate 5.18 – Grinding and rotomilling



90 Ed 2 / Rev 0

ANNEXURE R83/3 - REQUIREMENTS FOR TECHNICAL PROCEDURES

A2 MATERIALS

A2.6 CURING COMPOUND

The intent of the specified testing regime is to ensure that:

(a) the compounds being used in the Works are actually those which were proposed, and;

(b) that they comply with the specification.

A 3-stage testing program (as depicted in Plate A2.1) is used with the intent of maximising the chances of identifying nonconforming product whilst moderating the amount and cost of testing.

There have been numerous instances over the past 20 years where nonconforming product has been used. This was sometimes by accident or misfortune but at other times it occurred with the knowledge of the contractor’s staff. On occasions, supply practices have posed serious doubts about the product being delivered. A few examples follow:

A compound was used (for several weeks) despite the test certificate showing that it failed to meet viscosity requirements. The contractor had been aware of this but had deemed the viscosity criteria to be unimportant.

A large order of drums was delivered to site without any labelling. The labels were applied at a later date by a representative of the supply company, apparently without prompting, which suggested that this was not an uncommon practice by that company (47).

Audit testing has shown on several occasions that the product being used was both different in nature (to the proposed product) and was nonconforming.

Infrared testing effectively provides a “fingerprint” of the product and is routinely used by the manufacturer. For this reason, R83 seeks to utilise those results to minimise the repetition of other (more costly) test procedures.

47 A case was reported in the USA where curing compound was used as an air-entraining agent.



Ed 2 / Rev 0 91

Plate A2.1 – Testing of curing compounds

Test Reference sample (i)

Initial delivery (ii) Subsequent deliveries (iii)

Non-volatile content

Efficiency index

Density

Drying time

Viscosity

Infrared spectrum (iii)

Notes (i) A particular product could remain unchanged for several years, in which case the

reference sample and associated test certificates could be the same age. In other words, the “reference sample” need not be renewed for each project.

(ii) Supervisors should check that this sample does come from the “initial delivery”. (iii) On large projects, client audits may warrant infrared spectrum testing.

A3 DESIGN

A3.2 SURVEY AT THE TOP OF THE UNDERLYING LAYER

A3.2.2 Survey Reports Prior to Placing Base

Levels must be .... surveyed using a flat based staff ....

The intent is to minimise penetration into the layer by a pointed staff. For example, penetration into a sprayed seal would negate the thickness of that layer, thereby inflating the apparent thickness of the next-placed layer.

A3.2.3 Redesign of Pavement Levels

The rate of level change .... must not be greater than .... 1.0 mm per metre ....

This is governed by ride quality criteria.

the revised crossfall .... must not vary .... by more than ± 0.3%

This is governed largely by surface drainage criteria.

A3.3 MIX PARTICLE SIZE DISTRIBUTION

Each of the two methods of analysis should be used to monitor combined gradings.

For routine quality control, the contractor will typically use Method A (calculation) to assess the influence of combining different stockpiles. The grading of aggregates may change throughout a project as quarry faces change, and Method A will indicate the influence of those variations.



92 Ed 2 / Rev 0

However, other factors can have an influence on the actual combined grading of the mix which goes into the Works. Examples are:

batching errors

poor mixer uniformity.

Hence, Method B (wet sieving) should be used periodically as a check of the end product(48) which is going into the Works.

A4 PROCESS CONTROL

A4.1 PLACING STEEL REINFORCEMENT

A4.1.1 General

A4.1.1.2 Splicing

Splices in reinforcing fabric must conform with AS3600 ....

The required splices (as shown in the following plate) will obviously need to be tied adequately to ensure mechanical interlock throughout the paving operation.

Plate A4.1 – AS3600, Figure 13.2.4

A4.1.2 Tiebars

(a) Design intent

Tied joints are designed to hinge but not to open (i.e. widen). If joint opening does occur, it will usually be as a result of inadequate tiebar design and/or poor construction techniques.

Tiebars are designed to act purely in tension, and they have inadequate sectional area to act in shear. To be effective, they must hold the joint faces in close contact so that shear transfer is achieved through aggregate interlock (in the case of induced joints) or via corrugations.

Bond failure inevitably occurs because of voids around the bar due to inadequate compaction.

Tiebar design is outside the scope of typical contracts and so is not discussed here (49).

48 In this case, it will be “end product” as supplied to the paver. This does not rule out the possibility that

factors such as segregation under the paver may create a different end product “in the Works”. 49 See Reference [3].



Ed 2 / Rev 0 93

Tied joints are assumed to give a high degree of load transfer, and this allows design of the pavement for a “with shoulder” condition (50). Designs for a “without shoulder” condition are substantially thicker and, for this reason, untied joints are located away from truck wheelpaths wherever possible.

Tied joints of this width have clearly suffered tiebar failure. Structurally, these pavements are now effectively in the “non-shoulder” condition.

Plate A4.2 – Tiebar failure

The full consequences of joint opening (i.e. tiebar failure) are significant, as follows:

fatigue life will be substantially reduced. Plate A4.3 indicates that (for the assumed conditions) failure of the tiebars would reduce pavement life from 40 years to about 12 years.

tiebar corrosion is likely to accelerate;

deterioration of the subbase will accelerate;

(In the case of lean concrete subbase (LCS), the increased shear loading from the base is likely to cause cracking in the LCS.)

ingress of water and sediments will accelerate, leading to a risk of accelerated pavement distress.

Plate A4.3 The effect of shoulder condition on fatigue life

0

10

20

30

40

50

60

180 200 220 240 260 280 300 320

Base thickness (mm)

Des

ign

life

(ye

ars)

Rural

- w

ith sh

ould

er

Rural - n

o shoulder

PCP150mm LMC subbaseSubgrade CBR 10%40 year rural distributionTraffic - 1 x 108 HVAG4% growth1.2 LSF

50 This load transfer is affected by mechanical interlock, and the sole purpose of the tiebars is to hold the

faces together.



94 Ed 2 / Rev 0

The type of construction-related tiebar defect is likely to vary according to the joint type, as follows.

(i) In fixed-form (manual) paving (and assuming that the tiebars have been fixed in position prior to vibration), pull-out failure is highly unlikely unless the compaction has been extremely poor and/or the mix has very low slump/workability.

However, full pull-out strength is less assured if the tiebars are pushed into the side of the slab (through drill-holes) after the vibrators have passed.

(ii) In slipformed edges (i.e. formed joints), the tiebars are typically pushed into the edge of slab just behind the conforming plate. In many projects, recompaction of the concrete around the bars has been inadequate and hence the ties will not achieve the design pull-out strength.

(iii) At central (induced) joints in slipformed pavements, the tiebars are typically either pre-placed in cages or are depressed into the slab behind the conforming plate.

Pre-placed ties are unlikely to suffer pull-out failure unless the compaction is extremely poor (from failure of a vibrator, for example).

With depressed ties, there is a risk of pull-out failure because the injecting action is often very fast and the low slump mix is inadequately recompacted around the bar.

In severe cases, there can be a slotted void above the bar which is likely to initiate premature fatigue cracking; see further discussion below.

The common indicators of depressed tiebars are deeper texture and a localised depression on the surface. Fine surface cracking may also be evident.

The deep texture typically indicates where the tines have found slurry which has been worked into the depression by an oscillating screed. The depression is often also an indication of poor recompaction of the slot above the bars.

(b) Voids above tiebars

These are a specific case of under-compaction and are referred to here as “slotted voids”. They are generated when tiebars are depressed through the surface of the formed slab without adequate recompaction of the concrete along their path of injection.

Slotted voids weaken the slab in the same way as sawcuts. They are far more damaging than discrete random voids because their orientation induces high concentrated stresses in a zone/axis which is subjected to flexural stress from both traffic loading and curling effects.

The impact of slotted voids can be gauged by reference to the process for installing “slotted tiebars”. This process was used on a small number of sites in the late 1980s prior to the introduction of cross-stitching.

In this process, tiebars were epoxied into a slot formed by making two parallel sawcuts to half-depth in the slab. Plates A4.4.3 and A4.4.4 show examples. Cracking was commonly generated within 5 years of the operation, and so the process is no longer used.

The only viable disposition to slotted voids in new work is replacement of the full paved width.

There appears to be a correlation between slotted voids and the workability of the mix. This is not surprising because a low workability mix will obviously require increased compactive effort to fill any generated voids. In some cases, the marginal workability has been associated with the use of manufactured fine aggregates.

Supervisors should therefore be alert to the risk that slotted voids may be an intermittent phenomenon associated with random issues such as:



Ed 2 / Rev 0 95

batches of lower slump mix;

batches which have exceeded their forming time.

Tiebars

Plate A4.4.1 Voids above tiebars which had been depressed during slipform paving.

Plate A4.4.2 Voids above a tiebar which have been exposed by sawing along the line of the bar.

Plate A4.4.3 (above) Multiple cracking initiated by slotting.

Plate A4.4.4 (right) Corner cracking initiated by slot placement of a tiebar.

Plate A4.4 – “Slotted voids” above tiebars

A4.1.2.2 Location and Compaction Testing

Location surveys should commence within days of the Paving Trial.

On some past projects, surveys have not been started until several months after the commencement of paving, by which time there were several kilometres of nonconforming tiebars.

Plate A4.5 shows an example of a report sheet showing nonconforming tiebars within the central sawn joint.

In preparing cores for compaction testing, it is critical that surface voids be filled before deriving the specimen volume (using the water-displacement method); see Section A5.2.3 for discussion.



96 Ed 2 / Rev 0

Plate A4.5 An example of the nonconforming results from a survey of tiebar locations using a metal detector. The core above shows the damage caused by a tiebar crossing a contraction joint.

A4.2 PRODUCTION AND TRANSPORT OF CONCRETE

The Contractor's production and transport must be such as to:

(b) supply a homogeneous product ....

Note also Clause 7.5.3 of Specification Q6 states:


These clauses, used either alone or in combination, will often provide adequate grounds (even without extensive testing) to judge a product and/or process to be nonconforming.

The Contractor's production and transport must be such as to:

(c) result in .... workability .... which is compatible with the .... equipment ....

Refer to Section 4.2.2(g) for further discussion.

A4.2.1 Strength Testing of Production Mixes – Flexural and 7-Day Compressive

A4.2.1.1 7-Day Compressive Strength

The technical literature indicates that 7-day strengths are not always a reliable indicator of 28-day or 90-day strength. However, this finding must be taken in context with the scope of the work upon which it was based.

It appears true that an individual pair/set of 7-day results cannot be reliably extended to predict a later-age (individual) result, but there is sufficient experience to show that, for a single mix produced under repeatable conditions (as is the case on major paving contracts), rolling averages provide a valuable indicator of significant changes in mix characteristics.

This has been demonstrated on several projects where substantial 28-day cylinder failures could have been anticipated on the basis of 7-day results, but the contractor had not been monitoring



Ed 2 / Rev 0 97

or analysing the 7-day results. As a consequence, mix design adjustments were needlessly delayed by several weeks. In one case, several kilometres of nonconforming paving was completed during this period.

As stated above, any analysis must be limited to a single mix produced under repeatable conditions. Hence:

results for slipform and hand mixes must not be grouped;

if a mix is adjusted (by the addition of, say, 10 kg of cement) the results for the two mixes must not be combined.

A4.2.1.3 Flexural Test Specimens

Specimens must be moulded in accordance with Table R83.7 ....

Note that Table R83.7 requires moulding in accordance with Test Method T304, not AS1012.8.

The methods stipulated in T304 for compaction of steel fibre reinforced concrete (SFRC) in flexure specimens are intended to minimise the adverse (vertical) orientation of fibres within the tensile zone.

A4.2.1.4 Assessment of 7-day Flexural Strength

Comments under Section A4.2.1.1 regarding cylinder strengths apply also to 7-day flexure results.

A4.2.2 Mixing, Transport, Consistence and Air Content

.... after the completion of batching, the entire batch of concrete must be discharged from the mixer before any further charging takes place.

Site staff need to be alert to the practice of adding fresh ingredients to concrete which remains in a truck-mounted mixer (agitator) from a previous batch. This practice is permitted under AS1379 under certain conditions.

It is theoretically possible that remnants (which could involve several cubic metres) could be re-cycled many times over. In other words, an agitator can theoretically deliver many loads (to different clients) without ever fully discharging. Concrete crews typically refer to these as “hot” loads.

This practice is understood to have been motivated (justifiably) by concerns regarding conservation of resources, and is probably acceptable in many low-demand applications.

However, it is unacceptable in road paving because:

in order to maintain reasonable workability at later ages, a batch like this is likely to require a high water-cement ratio, and this would increase as time passes, without any obvious increase in slump or workability, but with undesirable consequences as discussed in Section A4.2.2(f);

the batch is likely to lose workability at a faster than normal rate, which increases the risk of an under-compacted slab with poor ride qualities.

The nett impact of premature pavement replacement would be an unjustified waste of resources, clearly contrary to the original intent of the practice.



98 Ed 2 / Rev 0

Mixing, transport and consistence must comply with AS 1379, Sections 3 and 4 and Appendix A, subject to the following provisions ....

Note that only specific clauses from AS1379 are adopted, and not the full Standard.



Ed 2 / Rev 0 99

BACKGROUND NOTES

Concrete mixing

Concrete uniformity is a critical requirement for good concrete (51) but is an aspect which generally appears to receive inadequate attention throughout the construction industry. The USA National Materials Advisory Board [28], states that “although large-scale fabrication plant and small-scale truck drum mixers have been used for years, much remains unknown about their operation and effectiveness.”

Experience with mobile mixers on RMS projects (for example) indicates that inadequate mixing is a recurring issue. This experience is supported by convincing anecdotal evidence from the wider construction industry.

Demonstration of this is the evidence of widespread confusion over the difference between “mixing” and “agitation”. Agitation during transit is commonly but incorrectly counted as “mixing time”.(52)

The following issues need to be understood with regard to site control of mixing operations:

Mixing does not technically nor contractually commence until all ingredients are in the bowl. In other words, the charging period does not count towards mixing time. This is justified because some constituents may not be added until late in the cycle.

Mixing must be carried out at a specified high speed and for a specified minimum number of revolutions.

For practical purposes, this is typically converted to a specified mixing period (at the specified speed). In a mobile mixer, thorough mixing will typically require 50 to 60 revolutions at 15 to 20 revs/min. Hence, minimum mixing times will typically be around 3 to 4 minutes.

By contrast:

Agitation is at low speed, typically about 4 revs/min.

Agitation does not contribute to mixing because it is too slow to provide any worthwhile shearing or particle collision and therefore does not constitute part of the mixing period. Its action is analogous to turning over shovels of concrete in a barrow; it merely turns over clods of concrete without achieving effective particle mixing.

Agitation applies during transit (when higher speeds would be dangerous) and during waiting periods. Strictly speaking, therefore, the term “transit mixer” is a misnomer.

Retempering: After any retempering (or addition of any other ingredient such as super-plasticiser), the full period of mixing must be provided in order to achieve uniformity.

Random observations at city building sites indicate that remixing typically ranges from 15 to 45 seconds, compared with the 3 or 4 minutes which would be required to achieve uniformity under AS1379.

Central batch mixers

51 By definition, concrete is “a thoroughly mixed combination of (ingredients) ….”. Hence, poorly mixed

concrete is clearly nonconforming. 52 The terms “agitator” and “truck-mounted mixer” normally refer to same vehicle. However, there are

several permutations in their use, as follows: (i) If ingredients are conveyed separately into the truck, then it is truly acting as a mixer as well as an

agitator. (ii) If the concrete is actually mixed in a fixed mixer prior to discharge into the truck, then the truck is

acting only as an agitator. However, if the mix is retempered then its role changes to that of a mixer.



100 Ed 2 / Rev 0

Mention was made in Section 4.2.2 of problems encountered on some projects resulting from adverse interaction of admixtures. In at least one of those cases, the problem seemed to have been exacerbated by the fact that mixing times were substantially shorter than those typically required to achieve mixer uniformity.

Plate A4.6.1 Cores exhibited distinctly non-uniform drying after saturation. The “wet” areas were those where admixture dosage and air content were highest.

Plate A4.6.2 The fractured slabs showed clear “marble-cake” composition. Note the horizontal lenses of mortar (outlined).

Plate A4.6 – Non-uniformity related to admixture interaction

On another project of about 10 km of divided carriageway, problems were encountered on just a few discrete days’ paving, whilst batching on the balance of the work appeared to be satisfactory.

As shown in Plate A4.7, batching records for those lots indicated various nonconformities. Cores from the pavement displayed clear non-uniformity, including very obvious sandy lenses within the central zone.

Plate A4.7 – Variability due to mixer non-uniformity

Batch variations (kg/m3)

Sand Coarse aggregate Cement

Allowable 850 – 870 ( 10)

1025 – 1055 ( 15)

275 – 285 ( 5)

Actual 895 – 935 (+25 to +65)

1010 – 1085 (–15 to +30)

275 – 300 (o to +15)

Cylinder strengths (MPa)

Cylinder unit mass

(kg/m3)

Core strengths (MPa)

Core unit mass (kg/m3)

34.5 – 56.5 2360 typ. 18.0 – 49.5 2270 – 2430 (96% - 103%)

These lots suffered longitudinal cracking prior to opening to traffic. The cause of the problem was not determined but it seemed to be related to mixer non-uniformity rather than being paver-related.

The above cases hopefully demonstrate that mixer uniformity cannot be taken for granted, even using modern computerised batching plants.



Ed 2 / Rev 0 101

Plate A4.8 This severe susceptibility to segregation (in lean-mix concrete subbase) was largely corrected by increasing the mixing time.

END OF BACKGROUND NOTES



102 Ed 2 / Rev 0

A4.2.2 (resumed) Mixing, Transport, Consistence and Air Content

(a) Mixer uniformity testing - general

A distinction is made at this point between:

(i) "within-batch" uniformity, and

(ii) "between-batch" uniformity.

Mixer uniformity testing is intended primarily to assess (i) but any irregularities in (ii) that are detected during testing would warrant investigation.

Uniformity testing requirements in R83 have been derived by supplementing the requirements of AS 1379. In the case of batch mixers, for example, conformity is required for three consecutive batches. (Again, this is intended to confirm the “within-batch uniformity” rather than to check “between-batch uniformity”.)

Plate A4.9 In some cases, the only difference between good and bad concrete is the uniformity of mixing.

Good concrete is made from:

good cement good aggregates, and good water

Bad concrete is made from exactly the same!

(b) Uniformity testing of central batch mixers

The batch is typically discharged into a tipper truck as shown in Plate A4.10.

Plate A4.10 Sampling procedures for batch mix uniformity.

Discharge length (L)Tray > 8m long

3 samples about 50 litres in sizeat 15%, 50% & 85% positions

Samples must betaken below 100mmfrom the surface

Batch mixers must be tested:

at the start of every project;

(to check that re-assembly has been satisfactory)

upon each 30,000 m3 production.

(to ensure that mixer wear has not reduced its efficiency).

The requirement for retesting at the start of each project is based on experience which shows that problems are often encountered after dismantling and re-establishing a batch plant. The Principal could review this requirement if the mixer has not been moved from its last project and its uniformity there was satisfactory.

Remember that, whilst the uniformity test is primarily intended to assess mixer uniformity, the opportunity should also be taken to check other issues. As an example, the grading results (from wet



Ed 2 / Rev 0 103

sieving) may have very good within-batch uniformity but nevertheless be consistently nonconforming in terms of the combined grading criteria. This would indicate a possible problem with aggregate gradings and/or with the batching process.

(c) Uniformity testing of mobile batch mixers

Under AS 1379 (and R83), every mobile mixer (agitator) must carry a compliance plate which details its minimum mixing requirements; see Plate A4.11. As an alternative, some companies have a system whereby the NATA certificate is held in the truck.

Plate A4.11.1 Extract from AS1379.

Plate A4.11.2 A typical identification plate.

Plate A4.11 – Mixer uniformity certification

However, AS 1379 does not require that each individual bowl be tested. A mixer is deemed to comply if “.... it is one of a series or a model of which at least one prototype has been tested and found to comply ....”. The test must be carried out using a mix “with a slump in the range of 40 to 80 mm ....”.

AS 1379 sets out requirements for subsequent re-testing (of old bowls) under circumstances such as “minor or .... major repair”, or where the mixing mechanism has “.... become worn ....” or where “.... non-uniformity of mixing due to wear is apparent”. However, there is no specified minimum frequency of re-test.

Clearly, many of these terms are open to subjective interpretation and so it is possible that poorly maintained bowls which are in regular daily use may not achieve uniformity within the specified mixing times.

Mixing occurs largely from the shearing action of the flights within the bowl but their efficiency will be significantly reduce if they are inadequately maintained. A common problem is the accumulation of dry concrete around the flights. Plate A4.12.2 shows two dislodged pieces which were discharged into an RMS project during 2002.

Hence, for example, a bowl may be of a design which was found (when it was new) to satisfy uniformity criteria for a 70 mm slump after a mixing time of 3 minutes. This bowl could be subjected to several years of regular use without the requirement for re-testing and so may not provide adequate mixing uniformity, particularly in lower slump slipform mixes.



104 Ed 2 / Rev 0

Plate A4.12.1 Typical layout of mixing flights.

Plate A4.12.2 Dislodged pieces of old accumulated concrete.

Plate A4.12 – Mixer maintenance

For these reasons, R83 adds further controls on mixing uniformity to those in AS 1379. For example, re-testing is required:

(i) every 24 months (but only on slump, air and unit mass);

(ii) upon evidence of non-uniformity of mixing;

(iii) if discharge times are uncharacteristically long (which could indicate worn and/or dirty flights).

At this stage, R83 stops short of requiring that all trucks be tested at the low slump values applicable to slipforming. However, supervisory staff should require the contractor to regularly monitor uniformity and to take effective action if any adverse signs are detected.

In all cases, the mixing criteria contained in R83 should be considered as minimum requirements, particularly for low slump mixes.

Under R83 (53) Clause 4.2.2(a), all mobile mixing in the project must take place at either the testing station or the point of placement. This was introduced in an effort to counter the recurring problems associated with inadequate uniformity.

It is worth repeating here that

Mixing must be carried out at a specified high speed and for a specified minimum number of revolutions.

In a mobile mixer, thorough mixing will typically require 50-60 revolutions at 15-20 revs/min. Hence, minimum mixing times will typically be around 3 to 4 minutes.

Special care is required in the mixing of steel-fibre reinforced mixes to ensure thorough distribution of the fibres; see discussion in sub-clause (e) below, and in Section A8.3.7.

(e) Compliance for uniformity

The mixer will be deemed to have passed the uniformity test if the differences .... for the corresponding properties of the three samples do not exceed the limiting values .... for any of the three consecutive batches....

53 Commencing from Ed2 Rev4.



Ed 2 / Rev 0 105

The requirement of this clause is that three consecutive batches must comply. (Note that Clause A4.2.2(b) also contains the requirement for testing of “three consecutive batches”.) On occasions it has been wrongly interpreted to mean that compliance can be achieved by achieving three non-consecutive conforming batches such as (for example) three “passes” which are spread throughout six or seven batches.

In practice, the client wants a high degree of assurance that every batch throughout the whole project will be “uniform”. An inability to achieve three consecutive passes during initial testing does not provide such assurance, and raises questions about the likely ongoing quality of the concrete.

Plate A4.13 shows the relevant tests required in the mixing uniformity evaluation along with the limits between samples as required under AS 1379.

Plate A4.13 – Uniformity tests required and limits of various properties

Property AS 1379 Limit on value differences

R83 requirements

Slump 10 mm SD 8 mm

Air Content 1% 4.5 1.5%

Mass per unit volume of plastic concrete

50 kg/m3 40 kg/m3

Coarse aggregated content 6% of mean No limit

Mass per unit volume of the air-free mortar

1.6% No limit

In the case of SFRC, it is also important that the fibres be thoroughly mixed. Attempts to establish tolerance limits for uniformity testing have been unsuccessful and it appears that little work has been done in this regard.

In the absence of such limits, efforts should be devoted to ensuring that the methods of incorporating fibres into the mixer are such as to reasonably assure their thorough distribution. This has proven to be a demanding task and appears to require the use of specialised equipment. A form of vibrating riffler has been used successfully for this purpose to break up the dense clustering of packaged fibres.

The sequence of charging is also reported to be critical [14].

Even under favourable conditions, fibre “balling” is likely to periodically occur and site staff should therefore add this to their surveillance list.

Plate A4.14 A fibre ball located in the washout sediment from an agitator.

American experience [15] suggests that fibre balls invariably result from inadequate initial dispersion and that they rarely develop during mixing. However, there are reliable anecdotal reports of local experience which refute this.



106 Ed 2 / Rev 0

(f) Retempering

The measurement and control of slump is one of the most contentious issues in concrete placement. The practice of "wetting up" the mix (retempering) is one which is discouraged by most consumers and designers but which is nevertheless an everyday occurrence in the construction industry.

Controls on retempering under R83 are based on the following issues. Plate A4.15 provides a graphical representation.

Loss of workability (or stiffening) in concrete derives largely from three sources:

- absorption of water by the aggregates

- evaporation

- hydration of the cement

the degree of hydration that occurs within the first 30 to 40 minutes will be minimal (under normal conditions of temperature and cement type).

water which is added within the first 30 to 40 minutes is essentially water which should have been added in the original batching and is therefore only a correction. (By the same reasoning, it will not increase the water/cement ratio beyond the intended value);

beyond about 30 minutes, hydration begins to account for an increasing proportion of the slump losses (and this will be more so at higher temperatures), and hence;

water which is added after about 30 minutes will be replacing not only that lost in evaporation and absorption, but also the component which has been lost to hydration, and replacement of this component will increase the water/cement ratio.

Plate A4.15 – Time limitation on retempering

R83 therefore only allows retempering under strictly controlled conditions. Such conditions can be justified by examination of the significant effects it can have on the concrete properties.



Ed 2 / Rev 0 107

For example, to increase the slump by 25 mm requires a water addition of about 10 litres/m3. Assuming this water is replacing purely hydration losses, the addition would also:

reduce the compressive strength by about 15% (5 MPa in a 35 MPa mix);

reduce the flexural strength by about 10% (0.4 MPa in a 4.5 MPa mix);

reduce the fatigue life from 40 to 20 years;

waste the equivalent of 30 kg/m3 of cement;

increase the shrinkage by about 10%;

increase the permeability by up to 50%.

It is important that all site staff understand these consequences of retempering on the properties of concrete.

Given these consequences, it is far preferable to control or adjust slump losses using admixtures (such as plasticisers) rather than water.

The above logic applies equally to the practice of allowing an over-wet batch to dry back into a conforming slump. A batch which is allowed to dry back by, say, 25 mm will obviously retain the properties of the initial high slump mix. Hence, the practice of drying back is misleading and nonconforming. For this reason, R83 requires that the slump be tested within a specified time period and that a decision be made without delay on its acceptance or otherwise.

Another industry practice is to dry back a wet batch by adding fresh (dry) ingredients, but this is also not allowed under R83 (or R82) unless it is completed before “completion of batching” (as defined).

The practice of drying back should not be confused with the requirement that a failed initial slump should be repeated (immediately); see further discussion in Section A4.2.2(h).

Concrete which is delivered by other than a mobile batch mixer must not have water or any other ingredient added to the mixed batch.

It is sometimes argued that the auger on a slipformer is an effective mixer. This is obviously not tenable and so there will never be acceptable grounds for spraying water on concrete which is spread in front of a paver. The resulting concrete would clearly not comply with the requirement for a uniform and homogeneous mix (51). Plate A4.16 shows two examples.



108 Ed 2 / Rev 0

Plate A4.16 Unacceptable practice of spraying water onto concrete which is spread in front of a paver.

.... Immediately after retempering, the mixing mechanism must be operated .... for not less than the mixing time determined under Clause 4.2.2(a) ....

Previous versions of this clause allowed a reduced mixing time (compared with the time at initial batching) but this was unjustified. Under AS 1379, “the mixing time .... shall be measured from the time all the ingredients are in the drum”. It follows, therefore, that if fresh ingredients are added (such as water) the full mixing time will be required in order to disperse those ingredients throughout the batch.

Retempering must only take place in the presence of the Contractor's representative ....

If surveillance uncovers retempering being carried out elsewhere, review is required of the contractor’s Quality System.

(h) Slump Testing

Slump testing is carried out using the sequence described in Clause A4.2.2(h) and as shown in Plate 4.17.

SD <= 8.0mm SD > 8.0mmContinue 6 con. loads

Non-conforming slump6 consecutive loads tested

Slump every 4th load(Visual check intermediate load)

SD <= 8.0mmProcess Slumping

SD > 8.0mmContinue 8 con. loads

Initial 8 consecutive loads



Ed 2 / Rev 0 109

Plate A4.17 – Frequency of slump testing.

.... if the measured slump is not within the specified limits, one repeat test must be made immediately from another portion of the same sample.

It is possible that a nonconforming slump could simply be due to inadequate mixing; see discussion in Section A4.2.2. In the case of mobile-mixed concrete, this can be dealt with as follows.

If the full period of mixing has been witnessed at the place of slump testing (prior to slumping) then this possibility can be ruled out, and any re-test must be carried out on “another portion of the same sample”. It must be carried out “immediately”, i.e. before any measurable drying out occurs.

However, if a slump fails under circumstances where doubt exists about the adequacy of mixing then it is recommended that a further full period of mixing be carried out before the re-slump (54). Obviously, the re-slump would not be carried out on “another portion of the same sample” (which is under suspicion of being under-mixed) but rather on a new sample taken after completion of re-mixing.

The re-slump must be carried out immediately after the re-mixing (i.e. before significant drying occurs) and without retempering. The following actions would then be appropriate:

(i) if the measured slump is not within the specified limits, one repeat test should be made immediately from another portion of the same sample (in order to ensure that the test procedure was not at fault);

(ii) if the re-slump value exceeds the limit, the batch must be deemed nonconforming (55);

(iii) if the re-slump value is below the limit, it may be retempered if all relevant conditions are met (regarding its age etc), otherwise the batch must be deemed nonconforming (55);

(iv) if the re-slump is conforming then the batch could be accepted, except that this would be an indication that routine mixing procedures are inadequate and hence the contractor should be required to review his system procedures to prevent a recurrence.

(i) Air Content Testing

Air entrainment is typically specified for the following purposes:

to reduce or control bleeding of the fresh mix;

to improve workability and slipformability;

to reduce the risk of freeze-thaw damage.

Entrained air will theoretically reduce the strength of the concrete in the same way as entrapped air does; see Section 5.2 for discussion.

However, entrained air improves the workability to the extent that the water/cement ratio can typically be reduced, and this reduction largely compensates for the strength loss.

The technical literature indicates that the optimum level of entrained air (in terms of strength compensation) is around 5%. At levels above about 6%, the strength of the concrete declines because the reduction in water/cement ratio (for similar workability) becomes less effective in balancing the increased air content.

54 Given the value of a batch of concrete, it would seem worthwhile to spend another three to four minutes in

mixing if there is a reasonable chance of redeeming it within the conditions of the specification. 55 ~ and there is no action available under R83 which will allow adjustment and/or reconsideration of the

batch.



110 Ed 2 / Rev 0

The physical distinction between entrained and entrapped air is imprecise but can be generalised as follows (56):

entrained air voids are typically between 10 m and 1 mm in diameter and are effectively spherical;

entrapped voids are typically larger than 1 mm in size and are irregular in shape.

Testing .... must be on batches of concrete from which cylinders are moulded .... under Clause 5.3.

In the event of nonconforming (or inconsistent) cylinders or beams, air content data are likely to assist in assessing the cause(s) of the problem.

.... if the measured air content is not within the limits specified, one repeat test must be made immediately from another portion of the same sample.

This provision for re-testing is not intended to highlight non-uniformity within the sample, but rather to indicate whether the first test was flawed.

Notwithstanding, the possibility of non-uniformity shouldn’t be ruled out and should be investigated if evidence exists.

In the case of agitator deliveries, re-mixing of the batch should be considered because the entrained air level can fall during longer hauls. Remixing may be successful in regenerating the air level into the specified range (and will also improve uniformity).

.... concrete with an air content higher than the specified range will be nonconforming and must not be used in the Works.... (except) .... may be used in anchors and subgrade beams subject to conformity with the relevant requirements.

The batch is required to conform on all criteria except for air content.

.... concrete with an air content of less than the specified range .... may be incorporated into the Works conditional on the conformity of the compressive strength of cores from that specific load ....

If the air content is low then, for similar workability (slump), the water/cement ratio will theoretically be higher than a similar conforming batch. Good control dictates that the influence of such variations should be monitored by the contractor.

AEA should never be used unless it will be regularly monitored, tested and controlled. Examples are known of projects where testing for air content didn’t start until several weeks after the commencement of paving, at which time the results were around 15%. The effect was to reduce a 35 MPa mix to about 20 MPa, with life expectancy of the pavement reduced to less than 10 years.

By contrast, however, there is ample experience over the past 20 years to show that close control can consistently produce entrained concrete with low variability in air content.

Whilst the specification allows a range of 4.5 1.5%, this full range is very rarely used on well controlled projects. Within-day variations, for example, are typically around 0.5%.

Any significant variations in air content should be investigated, as should any substantial variations in the amount of AEA required to yield conforming results. A graphic example is discussed in Section 4.2.2.

56 Source: ACI 116 “Cement and Concrete Terminology”



Ed 2 / Rev 0 111

BATCHING AND MIXING – CLOSING COMMENTS

The checks required by most specifications (including R83) are detailed and extensive. Despite the intensive efforts that are routinely devoted to ensuring conformity, unexpected outcomes too often occur.

The following examples quoted by Mather(57) demonstrate the point:

“I know of one plant where they found out (the hard way) that curing compound was a better air-entraining admixture than AEA was as a curing compound.”

“All the columns in the National Army Hospital were replaced because the concrete .... put in the forms had green aggregate (soft serpentine rock-soapstone) when it should have been black (basalt).”

“Is there cement in the cement bin and fly ash in the fly ash bin ? We had this problem on a dam where both bins were full of fly ash.”

There will never be a control system devised which guarantees the prevention of such occurrences, but Quality Assurance procedures aim to minimise the risks by putting procedures in place whereby even the most obvious features are periodically checked.

Site staff obviously need to be alert to practices which leave the project exposed to error.

Testing and surveillance practices are an obvious target. One growing practice which appears to invite trouble is that of allowing laboratory staff to take test specimens off-site for testing and reporting at a remote laboratory. It is strongly recommended that specimens be retained (or returned) for inspection by site staff as performance feedback.

As stated throughout this Guide, physical inspection of test specimens (by the contractor) should be considered an integral part of all testing programs.

To be of any value:

it must be carried out by staff who are familiar with batching and paving operations at that particular site (in other words, staff who will recognise any unusual features);

it needs to be done on a regular basis; this should be frequent early in the project and perhaps less so as the work progresses;

checks should be both before and after testing/crushing.

END OF CLOSING COMMENTS

57 Bryant Mather; US Corps of Engineers



112 Ed 2 / Rev 0

A4.3 PAVING CONCRETE

A4.3.1 Slipform (Mechanical) Paving

Key items such as vibrators and sensors must be monitored throughout the paving process.

Plate A4.18.1 Straight longitudinal cracking such as this (in contrast to randomly oriented cracking) can be an indication of a faulty vibrator on the slipforming paver.

Plate A4.18.3 (above) Subsequent coring yielded these voided specimens. The cause is thought to have been an irregularly operating vibrator.

Plate A4.18.2 (left) A project where surface voids were a recurring feature within the longitudinal bandwidth shown marked.

Plate A4.18 – Failure of paver vibrators

A4.3.3 Placing and Paving Operations

Place, pave and finish concrete so as to .... avoid segregation

Segregation has been the cause of many premature failures. In many cases, it will be immediately obvious, as shown in Plate A4.19.1.



Ed 2 / Rev 0 113

Plate A4.19.1 Extreme segregation of this type was one of the prime causes of the premature failures shown at right (in CRCP).

Plate A4.19.2 These failures are along paved edges in single lane paving

Plate A4.19 – Consequences of severe segregation

However, other cases will only be detected by close examination of paving operations, as in the example in Plate A4.20.

Plate A4.20.1 Segregation is not immediately obvious here, but probing in the mix above the vibrators revealed a substantial pond of slurry.

Plate A4.20.2 This was the edge produced by the paving shown at left. The outer top edge (for about 100 mm) was devoid of coarse aggregate.

Plate A4.20 – Consequences of segregation

To prevent the build-up of excess slurry like the cases above, the paver should have the facility to bleed the excess. Without this facility, or an acceptable alternative, the contractor cannot provide assurance that mortar pockets will be kept out of the Works. An example of a bleed chute is shown in Plate A4.21.

See also Section 5.2.1 regarding the risk of leaving slurry in transition lots.



114 Ed 2 / Rev 0

Plate A4.21 An example of a chute for bleeding excess slurry from the slurry box.

Place, pave and finish concrete so as to .... produce a uniform dense and homogeneous product throughout the pavement .... and .... expel entrapped air and closely surround all reinforcement and embedments ....

Plate A4.22 shows cores taken from pavements which would clearly not comply with these requirements.

Cores and cylinders are not intended purely for weighing and crushing; they should be regularly inspected for signs of inconsistencies such as segregation.

CRCP PCP LCS

Plate A4.22 – Examples of severe seg regation

Ensure that its workers engaged in paving operations have undergone the Concrete Paving Crew Training….

The Principal requires that the person in charge of the paving crew and at least half the remainder of the crew present at each separate concrete paving work must have undertaken the RMS “Concrete



Ed 2 / Rev 0 115

Paving Crew Training”. The training course covers setting formwork, stringlines and reinforcement; compacting concrete; placing and finishing concrete.

Extensive experience over the past 20 years shows that compaction is one of the most important of the processes which “directly affect quality” of concrete paving. Hence, there should be no doubting that the requirements of this clause are applicable to the compaction process.

However, the contractor may not always recognise what processes are critical or that they require documented procedures. RMS specifications often therefore specify those processes, and may also identify particular aspects of the process.

For compaction, these procedures are set out in R83 Clause A4.3.3.

.... the following parameters must be nominated ....

(i) maximum paving speed (i.e. instantaneous, not average),

If (because of factors such as irregular concrete supply) a paver makes progress during only 50% of the time then its average speed will be one-half of its instantaneous speed.

In other words, to achieve an average output of 1.5 m/min, the paver would have to pave at 3.0 m/min, and this would be fraught with risk.

Compaction, for example, in areas paved at 3 m/min will be much lower than in areas paved at, say, 1.2 m/min.

Plate A4.23 shows the preliminary results of RMS field trials on the influence of variable paving speed on compaction. Vibrators were dragged through a slipform paving mix over the range of speeds as shown, in an attempt to simulate the likely variability of unit mass at increasing distances from the vibrator(s). The dual-vibrator trials were carried out with a spacing of 500 mm.(58)

The results indicate that the between-vibrator densities are likely to drop substantially with increasing paver speed in excess of about 1.1 m/min. Within the vibrator path, the reduction in density is less pronounced but is still significant in the context of the specification acceptance criteria. The dual-vibrator results seem to confirm that a spacing of 500 mm may be excessive in practice.

Variable paving speeds will obviously produce variable pavement quality. There is a risk that this will not yield “a uniform, dense and homogeneous product throughout the pavement”.

Under this clause, the contractor is required to determine the maximum instantaneous speed at which its specific paver can reliably produce a conforming product.

58 The spacing of 500 mm is larger than is typically found in current local practice but was selected in order

to accentuate the between-vibrator density reduction.



116 Ed 2 / Rev 0

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

-200 0 200 400 600 800

Distance from Track (mm)

Dro

p i

n D

en

sit

y fr

om

Pe

ak

(%

)

800 s /m 3

600 s /m 3

400 s /m 3

200 s /m 3

Track Line

3.4 m

/min

0.85 m

/min

1.7 m/

min1.1 m

/min

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

-600 -400 -200 0 200 400 600

Distance from Track (mm)

Dro

p i

n D

en

sit

y fr

om

Pe

ak

(%

)

800 s/m3

600 s/m3

400 s/m3

200 s/m3

Track Line

3.4 m

/min

0.85 m

/min

1.15 m

/min

1.7 m

/min

Single vibrator

Dual vibrators

Plate A4.23 – Influence of vibrator speed and spacing (59)

.... target (optimum) paving speed,

This is the speed at which the contractor would plan to pave under ideal conditions (of mix properties and supply etc).

.... vibrator spacing, frequency and amplitude, and ranges thereof,

This requires that the contractor be familiar with the vibration characteristics of the specific vibrators on his paver. Every vibrator type has a different “radius of action” within which the concrete is exposed to the full compactive energy. The vibrators must be spaced closely enough to achieve a full overlap of influence between adjacent vibrators.

Further details are available in the RMS Concrete Pavement Manual [3], Section 10.4.

For manual paving, the following parameters must be nominated:

.... the size and number of vibrators, and .... the spacing of .... insertions

Manual paving has traditionally had a high incidence of compaction-related failures and so it is important that the contractor recognises the essential parameters for achieving conforming results.

For transition zones, the following information must be provided:

59 Each plot represents a different vibrator “drag” speed. The values shown in the box represent an

approximate equivalent vibration intensity in secs/m3.



Ed 2 / Rev 0 117

.... the proposed technique for paving at transverse construction joints, for both slipform and fixed form phases, at both the start and finish of paving runs ....

See Section 5.2 for discussion on the importance of this issue.

.... the distance between the transverse construction joint and the point of effective slipform vibration, at both the start and finish of paving runs,

See Section 5.2 for discussion on the importance of this issue.

.... proposals to ensure suitable workability for manual placement of the mix within the transition zone.

Machine and hand mixes have significantly different slumps, hence the compaction and finishing of a machine mix within the transition zone using manual methods will require intensive vibration to ensure conforming results.

A4.3.6 Texturing of Surface

R83 typically requires a combination of longitudinal hessian drag and transverse tining. The desired finish is shown at right.

Plate A4.24 – Texturing

The R83 surface finish comprises the following components:

a “sandpaper” finish (microtexture) as a consequence of the 40% sand content in the mix;

the hessian drag provides low levels of both microtexture and macrotexture, and assists in reducing the generation of tyre-related noise(60, 61);

60 A very smooth surface generates high noise levels. Steel-float finishes in multi-storey carparks are a good

example.



118 Ed 2 / Rev 0

the tining provides passages for the fast lateral dispersion of water.

The finished surface needs to be a balance between providing enough texture to ensure high skid values but not so deep that it will generate unacceptable levels of tyre noise.

Site staff should be alert to the problem of non-uniform texture depths. During tining, it is sometimes apparent that some areas of the surface are significantly wetter than adjacent areas. Where these areas originate from the same batch of concrete, it may be an indication of inadequate mixing, and this should be investigated as a first step, particularly where delivery is by mobile mixers; see Section A4.2.2 for further discussion.

A4.3.6.2 Transverse (texturing)

The use of long flexible tines (as shown in Plate A4.24) allows earlier tining than is the case with shorter tines. In turn, this enables curing to proceed as soon as the low-sheen surface condition is reached, and hence reduces the risk of plastic shrinkage cracking.

Short stiff tines are more likely to scratch the surface and dislodge aggregate, and hence normally can’t be used until much later than flexible tines.

The specified tine spacings are based on substantial local and overseas experience and shouldn’t be changed [13]. Cases are known in America, for example, where seemingly small changes to standard patterns have created significant problems.

A4.3.7 Curing

Spray bars and lances must be fitted with protective hoods to minimise the drift of curing compounds to workers and roadside areas.

The curing operations shown in Plate A4.25.1 resulted in curing compound being sprayed onto workers and passing vehicles. In addition to the OHS and public claims issues involved, the high losses (of compound) meant that the calculation of average application rate was meaningless.

Plate A4.25.1 Single nozzle lances typically give a highly variable application rate, particularly in windy conditions.

Plate A4.25.2 Multi-nozzle bars (hand-held) are allowed for smaller paving widths. The application rate will be more uniform than from single-nozzle lances.

61 A hessian drag is not suitable for SFCP; see Section 4.3.6.



Ed 2 / Rev 0 119

Plate A4.25.3 Spraying under exposed windy conditions dictates the use of covers to protect workers and the passing public.

Plate A4.25 – Spray curing

A4.5 JOINTS AND EDGES

A4.5.1 Sealants

Silicones have proven to be very resilient in pavement applications as long as they have been properly installed and designed (for dimensions).

The most common causes of premature distress are likely to be:

(a) dirty and/or wet joint faces;

(b) installation depths which are either too large or too small;

(c) installation too soon before the concrete has hydrated sufficiently.

In terms of dimensions, the sealant must be thick enough to resist penetration (by objects like aggregate) and its shape factor must be within a suitable range.

Shape factor is the ratio of depth to width. Manufacturers typically recommend that this never be greater than 1.0, i.e. the width shouldn’t be greater than the depth. A high shape factor will yield a sealant which is resistant to stretching and so is prone to bond failure (i.e. adhesion failure). A sealant with a low shape factor is more likely to suffer cohesion failure, or tearing of the silicone.

Tooling of a sealant serves two important function, viz:

(i) to push the sealant against the faces (to improve bond), and

(ii) to form the upper meniscus (which reduces the sealant’s resistance to stretching).

Backer rods

Sealant manufacturers typically recommend that the backer rod be oversized (relative to the joint width) by about 5 – 6 mm in order to provide firm resistance when tooling the sealant.

A4.5.2 Transverse Construction Joints

The first-placed face must be dense and fully compacted .... Where the face is nonconforming or the edge is damaged, it must be reinstated or repaired prior to the placement of adjoining concrete ....

See discussion in Section 4.5 and 4.5.1.



120 Ed 2 / Rev 0

A4.5.3.1 Sawcutting

The surface of the transverse contraction joint must not exhibit more than .... edge ravelling and the cumulative length of ravelling .... must not exceed ....

Where ravelling exceeds the specified limits, one feasible remedial treatment (subject to the Principal’s concurrence) is to re-saw the joint to a larger width which will remove sufficient of the spalling. In general, epoxy repairs have had only limited success.

A4.5.3.2 Cleaning

Grit blasting must not be used.

Grit blasting is permitted in mature concrete (in maintenance operations) but is not permitted in young concrete because:

it generates dust on the joint faces which poses a risk of poor sealant bond;

it is unnecessary if initial sawing and cleaning operations have been completed properly;

it is likely to damage the joint by rounding the arrisses.

A4.5.3.5 Permanent sealing

At slab edges and formed joints, the permanent seal must extend down the vertical faces of joints and any underlying crack which exceeds 2 mm width.

See discussion in Section 4.5.2.

A4.5.5 Longitudinal Joints

A4.5.5.1 Condition of Formed Joints and Debonding

The first-placed face must be dense and fully compacted .... Where the face is nonconforming or the edge is damaged, it must be reinstated or repaired prior to the placement of adjoining concrete ....

See discussion in Sections 4.5 and 4.5.1.

“Intimate bond .... can induce spalling at arrisses and hence must be avoided.”

Plate 5.26 The absence of debonding in cases such as this is likely to lead to intimate bonding and thereafter to the formation of a parallel (unplanned) crack within the second-placed slab.



Ed 2 / Rev 0 121

A5 END PRODUCT CRITERIA

A5.2 CONCRETE COMPACTION

A5.2.1.1 Moulding and Testing of Cylinders

(c) The unit mass for a pair of cylinders will be the average of the two results unless they differ by more than 20 kg/m3 ....

A difference in excess of 20 kg/m3 is likely to indicate variability in either the moulding procedures or the testing procedures, or both.

.... a statistical check must be made to determine the rolling cylinder unit mass (RCUM) ....

The RCUM is calculated in order to minimise the impact of between-batch variations in entrained air content.

(Whilst the specification allows a range of 4.5 1.5%, the short-term fluctuations (i.e. within any day) under controlled batching conditions should typically be within 0.5%; see further discussion in Section A4.2.2(i).)

The unit mass of flexure specimens .... must not be used in calculations of the RCUM.

Characteristic beam masses are likely to differ from cylinder masses because of the different specimen shapes. The method of compaction may also be different because table vibration is permitted for beams.

A5.2.1.2 Core Specimens

Cores must be placed within 2 hours of securing in either a tank of lime saturated water, or individual plastic bags, sealed to prevent water loss, and stored in the shade.

The cores must be kept in a moist condition in order to maintain equivalence with the reference cylinders. This will prevent drying, which could interrupt hydration and the potential increase in unit mass.

All cores must be tested for unit mass, and all results must be reported.

Selective testing and/or reporting is not permitted. Inconsistent results should be investigated.

A5.2.1.3 Frequency and Location of Coring for Compaction

Transition zones must form separate sublots.

Work within transition zones is invariably hand paved rather than machine paving and hence is separated from adjacent slipformed lots; see Plate A5.1 and discussion in Section 5.2.1.

The location of coring must be chosen in accordance with Figure A3.3 .... except .... as otherwise required by the Principal to assess process uniformity.

Cores within critical stress zones can initiate premature fatigue cracking and hence must be avoided unless they are needed to assess specifically targeted issues.



122 Ed 2 / Rev 0

A5.2.3 Core Testing for Unit Mass

The unit mass of the cores must be determined in accordance with AS 1012.12 Method 2

Method 2 requires measurement of the volume by water displacement method.

(b) assess cores .... for excessive voids and dress voids where warranted ....

The purpose of dressing is purely to derive the theoretical volume of the core if it were fully compacted and free of significant air voids, particularly around the perimeter.

Significant voids (if undressed) will fill with water and will therefore yield an artificially low volume when tested by immersion. In turn, this will yield an artificially high unit mass. (For this reason, no-fines concrete could theoretically conform for compaction if it were not dressed.)

By the same reasoning, it would be misleading to include the mass of the dressing as part of the initial mass of the core. Hence, the core mass must be determined prior to dressing. For consistency with the reference cylinders, the core mass must be a saturated value.

Care is required in techniques used for dressing of specimens. Plastic wrapping, for example, can trap a significant volume of air within the wrapping. Test Method T368 is therefore very specific in detailing the acceptable procedures.



Ed 2 / Rev 0 123

T = transition zone (Cl 5.2.1):- = 3 m (or as per Cl A4.3.3(viii))

Cylinder lots for; - strength (Cl 5.3.1) - RCUM (Cl 5.2.1)

Compaction lots & sub-lots (Cl 5.2.1)

Z

*7

Sub-lot A7A

Sub-lot A7B

Sub-lot B1A

Sub-lot B1B

Lot A7 Lot B1 Lot B2

T T

ZZ

Z

Lot B6

Lot B7 Lot C1 Lot C2

Sub-lot B7B

Sub-lot B7A

Sub-lot C1ASub-lot C1B

Z *7

T T

Z

Transverseconstruction joints

Plate A5.1 – Transition Lots and Sub-lots (slipform paving only)



124 Ed 2 / Rev 0

(f) the concrete age at testing must be between three (3) and seven (7) days;

This maintains consistency with the age of the cylinders at the time of testing unit mass.

(h) (i) non-concrete materials .... must be removed; and

(ii) up to 20 mm of concrete may be removed from each end of the core ....

Materials such as bituminous and wax interfaces must be removed.

Surface texture may also be removed, though its presence should not influence the result when volume is determined by the immersion method.

It is not the intent to allow the removal of sections which are seriously voided. In the event of dispute over a highly variable specimen, the lot should be assessed under Specification Q6 Clause 7.5.3 and R83 Clause A5.2.4.

If the core is to be subsequently crushed under Clause A5.3.3, further trimming may be required (after unit mass measurement) in order to meet the recommendation in AS1012.14 that “the preferred length/diameter ratio is as near as possible to 2:1”. (AS1012.14 also requires that cracked sections be removed prior to crushing.)

(j) individual results for unit mass must be rounded to the nearest 10 kg/m3 in accordance with AS1012.12.

It is very common to see results being reported to the nearest 1 or 5 kg/m3. These reports do not comply with AS1012.12.

(By contrast, it may be statistically valid to report the mean of a set of results to the nearest 5 kg/m3 but the mean must be calculated using values which are rounded to the nearest 10 kg/m3.)

A5.2.4 Within-core Variability

The purpose of this test is to guard against significantly variable compaction through the depth of the slab.

The presence of reinforcement (e.g. in PCP-R) can dampen the effectiveness of vibration and can result in lower compaction values below the steel than above.

The core must be prepared for testing by sawing into two cylinders of equal length with a tolerance of 20 mm.

Any steel reinforcement should be removed in order to minimise its potential influence on results.

A5.3 CONCRETE COMPRESSIVE STRENGTH

A5.3.2 Cylinder Strength Testing

.... as soon as ten pair results become available, the following condition will apply.

If the mean of such differences for ten consecutive pairs (up to and including that in question) is greater than or equal to 5% of the mean strength value for all twenty cylinders, then the compressive strength for a pair must be taken as the average of the two values.



Ed 2 / Rev 0 125

This clause becomes effective if there is a high incidence of significant within-pair variability in cylinder strengths.

Plate A5.2 demonstrates its use to determine the strength of Lot 333, as follows:

The mean of the 10 consecutive strength results = 36.1 MPa. (calculated using individual results, not pair averages)

The mean of the differences in the last 10 pairs = 2.3 MPa

Expressed as a % of the mean strength from those 10 pairs: 2.3 36.1 = 6.2%.

This exceeds the 5% limit.

Hence the strength of Lot 333 is taken as the average of the pair, i.e. 36.0 MPa rather than the higher value (38.0 MPa)

Plate A5.2 – Example of the cylinder strength results from 10 lots

Corrected 28-day strength (MPa) Lot

Cyl 1 Cyl 2

Avge of pairs (MPa)

Diff. of pairs (MPa)

% diff

324 30.0 33.5 31.8 3.5 11%

325 31.0 32.0 31.5 1.0 3%

326 35.0 38.5 36.8 3.5 10%

327 34.5 37.0 35.8 2.5 7%

328 38.0 39.0 38.5 1.0 3%

329 35.0 39.0 37.0 4.0 11%

330 40.0 40.0 40.0 0.0 0%

331 37.5 39.0 38.3 1.5 4%

332 35.0 36.5 35.8 1.5 4%

333 34.0 38.0 36.0 4.0 11%

= 36.1 = 2.3

A5.3.3 Core Strength Testing

Note that core strength testing is only initiated via a compaction nonconformity; see comments under Section 5.3.3.

for slipformed base, three cores must be taken at locations separated by at least one quarter of the length of the lot;

The requirement for the three cores should not be confused with the intent of AS1012.14 Clause 8 which states in part: “For a group of three cored specimens secured from the same location, .... the accuracy is ....”.

Under Clause A5.3.3, it is not purported that the three cores are “secured from the same location”. Rather, the intent is that three single cores be taken from separate locations in order to assess both the absolute strength levels and the variability within the lot.



126 Ed 2 / Rev 0

However, if there is valid reason to suspect that the result from one or more of those single cores is unrepresentative of the concrete at that location then there may be a warrant to take additional cores (i.e. invoke AS1012.14) in order to qualify that result. In this case, the intent of AS1012 would be to take the additional core(s) very close to the original, hopefully so that all results from that location derive from the same batch (which is hopefully also homogeneous).(62)

Consistent with the intent of Clause A5.3.3, lot conformity under Clause 5.3.4 is conditional on the conformity of every core and not merely on the mean value.

Similarly, acceptance of a nonconforming lot (with deductions) is based on results of individual cores and not merely on the mean of the results.

(Coring is a potentially damaging operation which is sought to be minimised. Hence, core strength is not specified as a primary acceptance criteria and is only enacted as a secondary assessment procedure in the event of compaction nonconformity.)

for manually paved base, two cores must be taken at locations separated by at least one third of the length of the lot;

Manually paved work is usually more variable than slipformed work and so the reduced coring requirement may appear to be an inconsistency. To balance this, however, is the fact that manual lots are smaller (than slipformed lots).

The Contractor may not take additional cores for this purpose without the prior approval of the Principal.

Coring is a destructive operation which potentially jeopardises slab fatigue life and so its frequency should be minimised.

A5.3.4 Conformity for Strength

The difference in age correction factors for cylinders and cores recognises the influence of field curing (on cores) compared with laboratory curing (on cylinders).

The correction factors (for age and shape) must be applied to the unrounded strength.

In other words, the result is not rounded (to the nearest 0.5 MPa) until after application of the corrections.

A5.7 RECTIFICATION OF FINISHED SURFACE AND RIDE QUALITY

See discussion in Section 5.7.

62 If it is necessary to take two or three cores from the same slab, their locations should be selected to

minimise the risk of premature slab distress, hence cores should not be aligned along primary stress planes. These will typically be aligned longitudinally or transversely, hence cores should preferably be taken along skewed lines. Also, slab corners should be avoided because of the high local stresses in that region.



Ed 2 / Rev 0 127

ANNEXURE R83/8 – STEEL FIBRE REINFORCED CONCRETE

A8.3.2 Strength

The methods stipulated in T304 for compaction of steel fibre reinforced concrete (SFRC) in flexure specimens are intended to minimise the adverse (vertical) orientation of fibres within the tensile zone.

A8.3.3 Consistence

The slump range for fibre mixes is lower than for non-fibre mixes, for the following reasons.

The incorporation of fibres in a mix improves its cohesiveness but reduces its apparent workability. In other words, if two mixes (one a plain mix and the other fibre-reinforced) yield the same slump value then the fibre-reinforced mix is likely to have better workability under vibration. This is explained by the fact that the fibres act to reduce the slump (i.e. increase the cohesiveness), but this effect is largely negated by vibration.

Because of these differences, there is an increased temptation to retemper SFRC because its slump and workability will appear low in the mixer. There is a risk during the early stages of a project that staff who are unfamiliar with SFRC will over-wet the mix based on their experience with the visual assessment of non-fibre mixes. These issues should be discussed with batchers, testing staff and agitator drivers prior to the commencement of construction.

The nett effect of over-wetting will be that fibre reinforced batches which appear suitable in slump testing will subsequently prove unnecessarily wet under vibration in the work. The surplus water will reduce the quality of the concrete without improving its placeability.

For the same reasons, SFRC is likely to exhibit different behaviour to non-fibre concrete under Vebe testing.

A8.3.5 Air Content

The universal reluctance to use entrained air in SFRC is thought to be associated with concerns about its adverse effect on fibre pull-out strengths.

A8.3.7 Batching, Mixing and Transport

Like every other component of concrete, it is important that fibres be thoroughly and uniformly distributed throughout the batch. Attempts to establish tolerance limits for uniformity testing have been unsuccessful and it appears that little work has been done in this regard.

In the absence of such limits, efforts should be devoted to ensuring that the method of incorporation and mixing are such as to reasonably assure their thorough distribution.

(a) Incorporation

This has proven to be a demanding task and appears to require the use of specialised equipment. A form of vibrating riffler has been used successfully for this purpose to break up the dense clustering of packaged fibres.

The sequence of charging is also reported to be critical [14].

Even under favourable conditions, fibre “balling” is likely to periodically occur and site staff should therefore add this to their surveillance list.



128 Ed 2 / Rev 0

Plate A8.1 A fibre ball located in the washout sediment from an agitator.

American experience [15] suggests that fibre balls invariably result from inadequate initial dispersion and that they rarely develop during mixing. However, there are reliable anecdotal reports of local experience which refute this.

(b) Mixing

Non-uniform fibre distribution has been an ongoing concern over a long period. Given the similar non-uniformity problems which are periodically encountered with plain (non-fibre) mixes, there is a possibility that some of the SFRC problems are simply due to inadequate mixing (63). For this reason, R83 now requires additional mixing for SFR mixes.

A8.5 TEXTURING

Hessian dragging of SFCP will pluck the fibres from the concrete and leave an undesirably open surface.

Where traffic speeds are relatively low (below about 70 km/hr, such as in urban roundabouts), the surface texture need only be relatively light. For a concrete with adequate sand content, the surface finish produced by methods such as a light tining or medium brooming will normally provide adequate texture for skid resistance (64). In both cases, it is desirable to use relatively long bristles/tines (to facilitate earlier texturing) and a low angle of attack (to prevent plucking of the steel fibres).

Power trowelling is not allowed. It was used on a roundabout in NSW during the 1990s and has resulted in a low surface friction which required re-texturing after a series of skidding accidents.

A8.8 CONFORMITY FOR COMPACTION

In SFCP, compaction is just as important as in plain concrete. In addition to the usual benefits of good compaction, SFRC requires full and consistent compaction to achieve high fibre bond strength. The ACI [26], for example, recommends that: “For fibre-reinforced concrete, internal vibrators must be used at a closer spacing and for a longer period of time to obtain satisfactory results.”

63 With fibre-reinforced shotcrete mixes (for example), experience indicates that mixing times of 10 minutes

or more may be required to achieve uniform dispersion of the fibres. 64 A broomed texture can generate undesirable noise levels at higher speeds, but this is unlikely at lower

urban speeds.



Ed 2 / Rev 0 129

ATTACHMENT A – REFERENCES 1. “Pavement Design - A Guide to the Structural Design of Road Pavements”. Austroads, 1992.

2. “Form 76 - Supplement to the Austroads Guide”. Roads & Traffic Authority, NSW.

3. “Concrete Pavement Manual - Design and Construction”. Roads & Traffic Authority, NSW.

4. “Concrete Roundabout Pavements - A Guide to their Design & Construction”. Roads & Traffic Authority, NSW.

5. “Interim Guide to the Maintenance of Concrete Pavements”. Roads & Traffic Authority NSW, June 2000.

6. Pfeifer L. “Further Improvements of the Durability of Concrete Pavements by Using Higher Strengths”. 7th International Symposium on Concrete Roads. Vienna, Oct 1994.

7. Clarke S R. “Test Method for Liquid Membrane-Forming Curing Compounds”. CIA News (Concrete Institute of Australia) Vol 10 No 2, July 1984.

8. “One man’s quest for perfection”. Interview of Watts Humphrey (a software engineering manager) by Julie Robotham; Sydney Morning Herald, 3 Sept 1996.

9. Miller Dr P. “Miller’s Tales”. Journal of the Institution of Engineers Australia. Date unknown

10. Larson R M. Federal Highway Administration, Washington DC. Unpublished correspondence with RMS staff.

11. “Manual of Contract Documents for Highway Works”. Volume 1 Series 1000. The Highways Agency, March 1998.

12. “Concrete Basics - A Guide to Concrete Practice”. Cement and Concrete Association of Australia (CCAA), Second Edition, 1992. Cartoon figures in this Guide are used with the kind permission of the CCAA.

13. Dash D M. “Investigation of Noise Levels in Pavement Wearing Surfaces and Development of Low Noise concrete roads”. ARRB Road & Transport Research, Vol 4 No 3, Sept 1995.

14. Hodgkinson J R and Rizzotto F. “Steel Fibre Concrete used in Mechanised Highway Pavement Construction”. Concrete Institute of Australia's Concrete 95 conference, Brisbane, Sept 1995.

15. “Guide for Specifying, Proportioning, Mixing, Placing and Finishing Steel Fiber Reinforced Concrete”. ACI Materials Journal. ACI Committee Report ACI 544.3R, Jan-Feb 1993.

16. Reserved

17. Ayton G P and Haber E W. “Curing and Interlayer Debonding.” Proceedings 6th International (Purdue) Conference on Concrete Pavements. Indiana USA, November, 1997.

18. Raymond S. Rollings. “Concrete Pavements: It’s More Than a Thickness Design Chart”. Proceedings 7th International Conference on Concrete Pavements, Orlando USA, Sept 2001, p281.

19. Ayton G P. “A Recipe for Compaction of Concrete”. Proceedings 7th International Conference on Concrete Pavements, Orlando USA, Sept 2001, p361.

20. Neville Dr A. “The Question of Concrete Durability: We Can Make Good Concrete Today.” Journal, Concrete International, July 2000, pp21-26.

21. Srinivasan D. “Will there be self-curing concrete?” Journal, Concrete International, September 2000, p6.

22. “Concrete Vibration – What’s Adequate ?” Lars Forssblad and Stig Sallstrom. Journal “Concrete International”, September 1995, Pp 42-48.



130 Ed 2 / Rev 0

23. Jackson P A. “Continuously reinforced concrete pavement: A literature review”. Transport and Road Research Laboratory (UK), Contractor Report 127 (1988).

24. Tayabji S, Wu C & Plei M. “Performance of Continuously Reinforced Concrete Pavements in the LTPP Program”. Proceedings 7th International Conference on Concrete Pavements, Orlando USA, Sept 2001, p685.

25. Mather B. “Owner Responsibility in Quality Verification?” Concrete International, Feb 2002, p70.

26. “Guide for Consolidation of Concrete.” ACI Materials Journal. ACI Committee Report ACI 309R-96, p27.

27. “Report on the 1992 U.S. Tour of European Concrete Highways”. FHWA Publication No FHWA-SA-93-012 (1993).

28. “Nonconventional Concrete Technologies - Renewal of the Highway Infrastructure”. National Materials Advisory Board, National Research Council, USA. Publication NMAB-484, Washington DC, 1997.



Ed 2 / Rev 0 131

ATTACHMENT B – CHECKLIST FOR LABORATORY TRIAL MIX



Ed 2 / Rev 0 132

R83/R84 CONCRETE BASE Trial Mix – Checklist

Project: __________________________________________________________ Contractor: __________________________________________________________________

Mix type: Machine / Hand Other _________________________________ Base type: PCP / JRCP / SFCP / CRCP (circle one)

Reviewed by: _____________________________________________________ Contractor’s Mix Identification: ___________________________________________________

Date: ___________________________ Spec. version: Ed __ Rev ___

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or

RMS Test Method (3, 4)

Reference Document No. (In Submission)

Comments (5) or

if OK

Certification (3, 6) Conformity of the mix & its constituents

3.8.1 (b) (6)

Verification checklist 3.8.1 (d) Source Geological type Compliance with AS 2758.1 2.2 (d) AS 2758.1 Quartz/chert content 2.2 (c) & (f) ASTM C295

Alkali reactivity (8) Table R83.2 RMS T363

Fine aggregate (Source 1)

Supplier/Quarry (7):

Chloride ion content 2.1(b) Cl A2.1.2 (9)

(1) For simplicity, the term “R83” subsumes “R84” throughout this form. (2) For SFRC/SFCP, see also Annexure R83/8. (3) RMS requirements sometimes differ from Australian Standards. Where this applies, the test certificate must certify that testing has been in accordance with the RMS specification or Test Method. Test results must be not more than 12 months old. (4) All Australian Standards and RMS Test Methods include a section titled “Reporting” or “Report” or “Records”. Check that all relevant requirements are satisfied. (5) This proforma is intended primarily as a checklist. Additionally, test results could be included in this column to produce a summary for future quick reference. (6) The covering statement of certification is required to be signed by the prime Contractor. In accordance with Cl 3.8.1, this certification can also be taken to mean that the trial mixing complied with the Contractor’s

proposals under Cl 4.2 for batching, mixing and incorporation of materials. (7) Insert brief details of supplier & source. (8) Under T363, initial testing must be carried out using GP cement in lieu of type SL. Check that the results certify the use of type GP cement alone (without fly ash).



Ed 2 / Rev 0 133

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or



Comments (5) or

if OK Sulphate ion content 2.1(b) Cl A2.1.2 (9)

Bulk Density (10) Table R83.2 AS 1141.4

Water absorption Table R83.2 AS 1141.5 Soundness Table R83.2 AS 1141.24 Organic impurities Table R83.2 AS 1289.4.1 Sugar content Table R83.2 AS 1141.35 Non-plasticity (manuf’d sand only)

2.2 AS 1289.3

Source Geological type Compliance with AS 2758.1 2.2 (d) AS 2758.1 Quartz/chert content 2.2 (c) & (f) ASTM C295

Alkali reactivity (11) Table R83.2 RMS T363

Chloride ion content 2.1(b) Cl A2.1.2 (12)

Sulphate ion content 2.1(b) Cl A2.1.2 (9)

Bulk Density (13) Table R83.2 AS 1141.4

Water absorption Table R83.2 AS 1141.5 Soundness Table R83.2 AS 1141.24 Organic impurities Table R83.2 AS 1289.4.1 Sugar content Table R83.2 AS 1141.35

Fine aggregate (Source 2) Supplier/Quarry (7):

Non-plasticity (manuf’d sand only)

2.2 AS 1289.3

Source Coarse aggregate (Source 1) Geological type

(9) Cl A2.1.2 allows two alternative methods for assessing the ion contents. (10) In AS 1141.4 the uncompacted density is required to meet the criterion in the specification. (11) Under T363, initial testing must be carried out using GP cement in lieu of type SL. Check that the results certify the use of type GP cement alone (without fly ash). (12) Cl A2.1.2 allows two alternative methods for assessing the ion contents. (13) In AS 1141.4 the uncompacted density is required to meet the criterion in the specification.



Ed 2 / Rev 0 134

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or



Comments (5) or

if OK Compliance with AS 2758.1 2.3 AS 2758.1 Alkali reactivity (8) Table R83.3 RMS T363 Chloride ion content 2.1(b) Cl A2.1.2 (9) Sulphate ion content 2.1(b) Cl A2.1.2 (9) Bulk Density (10) Table R83.3 AS 1141.4 Particle Density Table R83.3 AS 1141.6 Water absorption Table R83.3 AS 1141.6

Material 75 m Table R83.3 AS 1141.12

Particle shape 2:1 Table R83.3 AS 1141.14 Particle shape 3:1 Table R83.3 AS 1141.14 Wet Strength Table R83.3 RMS T215 Wet/Dry variation Table R83.3 RMS T215 Weak Particles Table R83.3 AS 1141.32 Light Particles Table R83.3 AS 1141.31

Slag iron unsoundness (14) Table R83.3 AS 1141.37

Slag dusting unsoundness(14) Table R83.3 AS 1141.61 (15)

Supplier/Quarry (7):

Fractured faces Table R83.3 RMS T239 Source Geological type Compliance with AS 2758.1 2.3 AS 2758.1 Alkali reactivity (8) Table R83.3 RMS T363 Chloride ion content 2.1(b) Cl A2.1.2 (9) Sulphate ion content 2.1(b) Cl A2.1.2 (9) Bulk Density (10) Table R83.3 AS 1141.4 Particle Density Table R83.3 AS 1141.6 Water absorption Table R83.3 AS 1141.6

Coarse aggregate (Source 2) Supplier/Quarry: (7)


(14) Testing is required only for slag aggregates. (15) AS 1141.61 (1974) was withdrawn in 1998 but is still used for this requirement.



Ed 2 / Rev 0 135

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or



Comments (5) or

if OK Particle shape 2:1 Table R83.3 AS 1141.14 Particle shape 3:1 Table R83.3 AS 1141.14 Wet Strength Table R83.3 RMS T215 Wet/Dry variation Table R83.3 RMS T215 Weak Particles Table R83.3 AS 1141.32 Light Particles Table R83.3 AS 1141.31 Slag iron unsoundness (14) Table R83.3 AS 1141.37 Slag dusting unsoundness (14) Table R83.3 AS 1141.61 (15) Fractured faces Table R83.3 RMS T239 Source Geological type Compliance with AS 2758.1 2.3 AS 2758.1 Alkali reactivity (8) Table R83.3 RMS T363 Chloride ion content 2.1(b) Cl A2.1.2 (9) Sulphate ion content 2.1(b) Cl A2.1.2 (9) Bulk Density (10) Table R83.3 AS 1141.4 Particle Density Table R83.3 AS 1141.6 Water absorption Table R83.3 AS 1141.6


Particle shape 2:1 Table R83.3 AS 1141.14 Particle shape 3:1 Table R83.3 AS 1141.14 Wet Strength Table R83.3 RMS T215 Wet/Dry variation Table R83.3 RMS T215 Weak Particles Table R83.3 AS 1141.32 Light Particles Table R83.3 AS 1141.31 Slag iron unsoundness (14) Table R83.3 AS 1141.37 Slag dusting unsoundness (14) Table R83.3 AS 1141.61 (15)

Coarse aggregate (Source 3) Supplier/Quarry (7):

Fractured faces Table R83.3 RMS T239



Ed 2 / Rev 0 136

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or



Comments (5) or

if OK Combined particle distribution Table R83.5 Natural sand content of combined fine aggregates

2.2(b) Source documents

Sand content ( 38%)

3.3

ALD for 9.5, 6.7mm (16)

Table R83.3 RMS T235

Combined aggregates

ALD for 6.7, 4.75mm (16)

Table R83.3 RMS T235

Binders Cement type 2.4 AS 3972 PC (7): Cement source Fly ash type (fine grade) 2.4 AS 3582.1 FA: Fly ash source Minimum binder contents Table R83.6 (17)

Admixtures Types 2.5(c) & (d) Re / WRRe (7): (Circle type)

Overall material compliance 2.5 AS 1478 (Clause 1.7)

Calcium chloride, calcium formate, triethanolamine, other accelerators

2.5 Manufacturer’s Certificate (19)

Compatibility 2.5(a) Manufacturer’s Certificate (19)

AEA (7):

except SFRC (18)

Total alkali contribution 2.5(b) Impurity limits 2.9 AS 1379

Table 4 & Cl 2.7 Water (7):

(16) ALD testing is required on these specific fractions. AS 1141.14 (for particle shape) is limited to testing of the fractions larger than 9.50 mm, hence the purpose of this ALD testing is to control the shape of the smaller

fractions (which can have a significant impact on workability). (17) For SFRC/SFCP, see also Annexure R83/8. (18) Entrained air is not permitted in SFRC; see Clause A8.3.5. (19) A manufacturer’s certificate is satisfactory on the basis that the product has been tested in accordance with the Australia Standard.



Ed 2 / Rev 0 137

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or



Comments (5) or

if OK Source Source A8.4 Type & size A8.4

Steel Fibre

Fibre factor (F) A8.2 Equation Constituent quantities per yielded m3 of concrete

3.8.1(ii)(A)

Slump 3.6 AS 1012.3 Method 1 mm Vebe reading (slipform only) 3.6 AS 1012.3 Method 3 sec Bleeding Table R83.8 AS 1012.6 %

Fresh Mix

Air content Table R83.8 AS 1012.4 Method 2 % Compressive Table R83.7 (17) T304 Internal vibrator:

Make: Model:

Flexural Table R83.7 (17) T304 Indirect tensile

(100mm cyls (21))

Cl A3.8.1 same as compressive specimens (T304) (20)

Drying shrinkage Table R83.8 AS1012.13, with external vibration

Bleeding Table R83.8 AS1012.4, with internal vibration

Moulding & compaction of test specimens (20, 17)

Air content (18) Table R83.8 (18) AS1012.4, with internal vibration

Minimum compressive strength

Table R83.7 (17) Refer to Table R83.7 MPa @ 7D (13) MPa @ 28D

Hardened concrete

Minimum flexural strength Table R83.7 (17) Refer to Table R83.7 MPa @ 7D

(20) RMS moulding & compaction requirements are more stringent than those in AS1012. Check that moulding is certified to have been in accordance with the relevant Test Method and not merely in accordance with

AS1012. Check also that unit mass values have been reported for all strength specimens (for possible later comparison with field results). (21) This specification nominates 100 mm cylinders for Indirect Tensile (IT) testing, contrary to the AS1012.8 requirement for 150 mm cylinders. The purpose of IT testing in the trial mix is to enable possible comparison with

IT results from 100 mm cores from the pavement in the event of failure of standard flexural beam results. 150 mm cores are considered to be too destructive. In CRC pavements, IT strength is also used as an alternative input parameter for the design of the longitudinal steel content. In CRCP, a further objection to the cutting of 150 mm cores is that they would intercept this

reinforcement.



Ed 2 / Rev 0 138

Material or

Item Property

Clause or

Table No. (1, 2)

Standard or



Comments (5) or

if OK MPa @ 28D

Indirect tensile strength (21) 3.8.1(iii)(F) (report only)

AS 1012.10 MPa @ 28D

Drying shrinkage Table R83.8 AS 1012.13 Chloride ion content 2.1(b) AS 1012.20 Sulphate ion content 2.1(b) AS 1012.20

Comments:



Ed 2 / Rev 0 139

ATTACHMENT C – PAVING TRIAL CHECKLIST



Ed 2 / Rev 0 140

R83/R84 CONCRETE BASE Base Paving Trial – Checklist

Project: __________________________________________________________ Contractor: __________________________________________________________________

Pave type: Machine / Hand Identification (1)________________________ Base type: PCP, JRCP, CRCP or SFCP (circle one)

Contractor’s Trial Identification: ___________________________________________ Contractor’s Mix Identification: _________________________________________________

Reviewed by: _________________________________________ Date: __________________________ Spec. version: Ed __ Rev ___

Property or

Item Property

R83 Clause or

Table No.(2, 3)

Standard or RMS Test Method

(4, 5, 6)

Comments (7) or

if OK Approved mix? Concrete mix Mixing time 4.2.2 Test cylinders Table R83.7 (3.5)

A5.2.1.1 T304 (3) Internal vibrator:

Make: Model: Cores A5.2 A5.2

Moulding of test specimens (8)

Beams Table R83.7 (R83.16 for SFRC) (3)

T304 (3)

Air content R83.8 (3.7) AS 1012.4 (Method 2) with internal vibration

Supply & paving

Slump (mm) 3.6 AS 1012.3 (Method 1)

(1) Separate trials are required for each paver and Contractor’s paver identification is required. (2) For simplicity, the term “R83” subsumes “R84” throughout this form. Where a Table No is shown in this column, the clause number is shown in brackets. (3) For SFRC/SFCP, see also Annexure R83/8. (4) RMS requirements sometimes differ from Australian Standards. Where this applies, the test certificate must certify that testing has been in accordance with the RMS specification or Test Method. Test results must be

not more than 12 months old. (5) All Australian Standards and RMS Test Methods include a section titled “Reporting” or “Report” or “Records”. Check that all relevant requirements are satisfied. (6) In some instances the test requirements are a series of tasks detailed in the specified clauses of Annexure R83/3. (7) This proforma is intended primarily as a checklist. Additionally, test results could be included in this column to produce a summary for future quick reference. (8) For the trial the RCUM is taken as the mean of all 28-day pairs of cylinders and tested at an age as noted in Clause A5.2.1.1 (a). Also, refer to Annexure R83/3, Clause A4.4.



Ed 2 / Rev 0 141

Property or

Item Property

R83 Clause or

Table No.(2, 3)


(4, 5, 6)

Comments (7) or

if OK Forming time (min.) 4.2.2 (h)

Air temperature (C) 4.3.4

Concrete temperature (C) 4.3.8.1

Moisture loss prevention 4.3.5 Retempering A4.2.2 (f) Paving length (m) 4.4 Paving width (m) 4.4 Paving speed (m/min.) A4.3.3 (i & ii) Vibrators A4.3.3 (iii)

Mechanical paving operations (if required)

Gross operating mass A4.3.3 (iv) Paving length (m) 4.4 Paving width (m) 4.4

Manual paving operations (if required) Vibration practices 4.3.2 and A4.3

Subbase trafficking R82 4.3.8.4 Subbase loading & surface Debonding treatment 4.3.3 & R82 4.10

Longitudinal and transverse bar diameter and spacing

Drawings

Location tolerance 4.1.1 A4.1.2.2 Splicing A4.1.1.2

Steel reinforcement (if required)

Support A4.1.1.2 Manufacturer & type 6.1 & 6.2 Steel fibres (SFCP) Batching A8.3.7 Tiebar diameter and spacing Drawings Anchorage strength 4.1.2 (b) A4.1.2.1 Location tolerance 4.1.2 (c) A4.1.2.2 Proximity to joints 4.1.2

Tie bars (if required)

Compaction 4.1.2 A4.1.2.2 Dowel bar diameter and spacing

Drawings & 4.1.3 (h) Dowel bars (if required)

Galvanised, straight and coated

4.1.3 (b to d)



Ed 2 / Rev 0 142

Property or

Item Property

R83 Clause or

Table No.(2, 3)


(4, 5, 6)

Comments (7) or

if OK Debond stress 4.1.3 (d) T366 Dowel assembly 4.1.3 (g) Location tolerance & alignment

4.1.3

Texture 4.3.6 Texture depth Table R83.11 (4.3.6) T240

Surface finish

Saw-cut grooves (if required) A4.3.6.3 Concrete cracking Planned vs unplanned 5.1

Curing Compound 2.6 AS 3799 Line marking compatibility 2.6 R141 Application rate 4.3.7 (d to f) A4.3.7 Application extent 4.3.7 (e)

Curing

Film duration 4.3.7 (a & g) Transverse construction 4.5.1 A4.5.1

Transverse contraction (9) (R83)

4.5.2 A4.5.2

Longitudinal 4.5.4

Joints

Outer edge 4.5.7 Alignment tolerances 5.4.1 Level survey 5.4.2 A5.4.2.1 Thickness & for SFCP

5.4.3 & 5.4.4 6.7

A5.4.2.1

Geometry & thickness

Surface profile 5.5 Comments:

(9) In the trial pave, sealing of transverse and longitudinal joints is not required.