Concrete Pavement Upgrades - Tricks and Traps Papers/Paper 22... · rectification or justifying slab replacement. ... of the frequency of slab failures along the Upgrade. ... Concrete

Australian Society for Concrete Pavements Concrete Pavements Conference 2017

Concrete Pavement Upgrades – Tricks and Traps

Justin Moss, Grant Cheetham & Mark Kelleher (Arcadis)

Peter Carson & James Walker (Roads and Maritime Services NSW) Todd Myers (TSM Civil)

ABSTRACT

The widening, and requisite partial-rehabilitation, of a 30-year-old 8 km plain concrete dual carriageway pavement on the M1 Motorway 70 km north of Sydney is one of Australia's first pavement redesign and rehabilitation challenges for a so-called 'modern' concrete pavement. Along with the Tuggerah to Doyalson project, this design marks the beginning of a renewal phase for NSW concrete road infrastructure.

This paper reports on the analysis of data from a detailed photometric survey which provided a unique opportunity to study the long term performance of 7000 concrete slabs, many of which were misshapen (compared to contemporary design standards), as well as [the now deprecated] 6:1 skewed joints. Whilst excessively long existing fast lane slabs performed in similar manner to square slabs, the failure rate of fast lane slabs in superelevated pavement is eight times higher than in the non-superelevated carriageway sections. Corner cracking also occurs at twice the rate of slabs in superelevation.

A new alignment, carriageway widenings, thin pavements, staging under high traffic volumes, aquaplaning risks and joint selection all presented unique challenges in the course of this design. Lessons captured in this paper include the perils of adopting non parallel alignments, the importance of repair prioritisation, the value of field inspections, the efficiency of the consolidated slab replacement methodology, the merit of learning from local practitioners, the use of multi-criteria analysis to resolve design indecision and the application of trapezoidal slab thickening.

The main outcomes of this study are presented along with the recommendation that Roads and Maritime Services NSW consider the development of a ‘Concrete Pavement Widening’ guide which captures the aforementioned lessons and the recommendation that further photometric surveys be undertaken of pavements of a similar heritage

2 ASCP Concrete Pavements Conference 2017

Concrete Pavement Upgrades – Tricks and Traps; Moss, Cheetham, Kelleher, Carson, Walker, Myers

ABOUT THE PROJECT Location The site of the Kariong to Somersby M1 Motorway Upgrade is located between the Kariong and Somersby Interchanges approximately 70 km north of Sydney, and is approximately 8 km in length (refer to Figure 1). This motorway is one of Australia’s busiest non-urban motorways. The existing dual carriageway plain concrete pavement (PCP) was originally constructed in 1986 under two separate contracts. The motorway comprises of two dual-lane carriageways with some areas of three lane carriageway, typically at the extents of the project. The Kariong Interchange, located at the southern end of the project, features ramps and additional approach lanes which add approximately 30% of traffic southbound from Kariong towards Sydney.

Features of the Existing Pavement The existing motorway consists of many large radii curves with short isolated straights. There are a number of locations where stormwater flow-paths on the road surface present aquaplaning risks at superelevation transitions.

The 1986 PCP pavement was originally constructed with randomised transverse contraction joint spacings at a 1:6 skew (CCAA 1982) - both now deprecated joint design features. Longitudinal joints, tied or induced, are in similar positions respective to the wheel paths as per current practice.

The existing pavement is nominally 11.6 m wide (Refer to Figure 2) featuring:

• 3.7 m lanes

• 3.0 m nearside shoulder (incl. SH gutter in cuts)

• 1.2 – 3.0 m offside shoulder

Cores taken from the existing pavement indicate a mean compressive strength of 41 MPa for base and 32 MPa for subbase. Thickness of the existing base and subbase range between 215 mm and 250 mm and 140 mm and 170 mm, respectively.

Figure 2 - Typical Cross Section of Motorway

Figure 1 – Site location Kariong to Somersby NSW

ASCP Concrete Pavements Conference 2017 3 Concrete Pavement Upgrades – Tricks and Traps; Moss, Cheetham, Kelleher, Carson, Walker, Myers

Overview of the Upgrade Arcadis was engaged by RMS to undertake the detailed design of a mainline widening (including ramp upgrades), investigations and construction documentation using an earlier concept design and environmental assessment by Parsons Brinckerhoff. The concept design assumed a non-parallel control line, extensive individual slab replacement (prior to widening) and a preliminary prioritisation of repairs based on a photometric survey of existing condition.

The detailed design commenced in August 2015 with a target construction completion date of 2019.

The work to be carried out for the construction of the Upgrade consists of:

• Night work - high early strength slab replacements under traffic

• Daytime construction of an additional lane toward the median (both carriageways)

• Daytime consolidated slab replacements for existing failed fast lane slabs

• Widening of existing twin bridges over Gindurra Road

• Additional lanes for two on- and off-ramps at Kariong Interchange

• Construction of a wide flexible median shoulder for maintenance access (both carriageways)

• Diamond grinding the full width of both carriageways

Key sub-consultants on the project included TSM Civil (constructability), Golder Associates (geotechnical) and M.I. Engineers (contract documentation). Independent verification was undertaken by Aurecon.

Strategic and Design Objectives The primary objectives of the Upgrade were to:

• Improve freight efficiency and commuter movement by widening the motorway to three lanes,

• Improve safety for current road users (including cyclists and motorists),

• Manage disruption to traffic throughout the construction period to provide consistency to journey times,

• Reduce peak travel times and traffic speed variability, and

• Provide best value for money over its service life

Early Detailed Design In order to support the Upgrade objectives, Arcadis was required to:

• Optimise the design to ensure practical and efficient construction,

• Design the project works to limit adverse impacts to the natural environment, and

• Ensure temporary construction arrangements would minimise disruption to local and through traffic.

Arcadis’ preliminary review of the concept design identified key issues requiring further consideration:

• Pavement repair strategy – repair of current and anticipated failures and their impact on construction staging and completion date,

• Pavement repair reprioritisation – as a widening project (not rehabilitation project), rehabilitation needed only be undertaken to ensure new works would not be affected by existing infrastructure,

• Undesirable joint location and slab width arising from non-parallel design control line to existing pavement edges and joints,

• Limited allowance in staging for incident management, including narrower temporary traffic zone shoulder widths, together with breakdown bays, and

• Constraints in joint locations and slab width arising from crowning for the treatment of aquaplaning.



Key Constraints Key traffic management and timing constrains relevant to the Upgrade are as follows:

• Retention of the same number of lanes throughout construction, except where permitted as night works,

• Night work repairs must be completed and traffic-ready in one night shift (refer Figure 3)

• Tight deadlines for the completed Upgrade and therefore the detailed design, and

• Elevated target serviceability levels for incident management dictating wide shoulders for emergency vehicle and the availability of median crossovers during construction.

Figure 3 - Average traffic volume per hour


PAST PERFORMANCE OBSERVATIONS Preliminary Condition Assessment An early pavement options report developed by RMS concluded that the existing pavement was serviceable with acceptable roughness. Cracking, or crack-related issues, impacting approximately 10% of the pavement surface, were full depth and up to 20 mm wide in some areas. Deflection testing data indicated load transfer efficiency issues and possible voids under the slab. Thickness of the PCP base varied between 215 mm and 250 mm and the lean mix concrete (LMC) subbase was intact even under the cracked PCP base. Geotechnical test reports indicated the pavement was supported on a reasonably good quality sandstone subgrade.

As part of the concept design, a desktop photometric survey was undertaken which captured and analysed the entire concrete surface of the project. Of approximately 7000 slabs analysed (refer Figure 4 and Figure B 1) using the automated processes, and later interpreted by RMS, approximately 4% were identified for full slab replacement, 15% for partial slab replacement and 8% for corner slab replacement. Other repairs including cross-stitching, routing-and-sealing, and joint sealing were also recommended.

Arcadis undertook a treatment calibration inspection which sought to confirm results suggested by the photometric survey. The results are discussed later in this paper.

Slab Failure - Intensity Analysis For the purposes of the following discussion, “failure” is deemed to be any structural crack identified for rectification or justifying slab replacement.

An analysis of failure rates was undertaken during preliminary detailed design to obtain an understanding of the frequency of slab failures along the Upgrade. The outcomes of this review influenced the prioritisation and methodology of repairs. For this assessment, proposed locations for slab replacement in the existing fast lane were plotted against chainage. A simplified version of this analysis, with chainages grouped by 250 m increments, is provided in Figure 5.

Figure 5 - Intensity of fast lane slab failure rate per 250 m (black indicates a failure rate exceeding 50%)

It was noted during this analysis that failures tended to group together. Areas of high intensity failure typically did not overlap. Instead, the high intensity of failure appeared to oscillate between carriageways at certain points. Upon further investigation, it was noted that areas with high failure rates in the fast lane were generally coincident with superelevation, and, in areas where superelevation transitioned to normal crossfall, the failure rate noticeably decreased. High failure rates were not observed in sections of superelevation at the project extents. These relationships are reviewed in subsequent sections.

Figure 4 – Sample photometric output



Slab Failure - Slow Lane vs Fast Lane On multi-lane roads, heavy vehicles tend to stay in the left slow lane. Nearby Weigh in Motion (WIM) data for a three-lane motorway indicated the relationship in terms of Lane Distribution Factors (LDF) for the slow, middle and fast lanes is 0.7, 0.2 and 0.1, respectively. WIM data for two-lane sites indicates an LDF of 0.9 and 0.1 for slow and fast lanes, respectively. It is reasonable to expect that failure rates would follow a similar distribution, noting exceptions arising from improved nearside shoulder slab support and the restraint provided to the slow lane by the fast lane.

An analysis was undertaken to compare the occurrence of cracking between the slow and fast lane. Three types of structural failure were considered: transverse cracking, longitudinal cracking and corner breaks. The analysis produced results against the above expectations and are contained in 0.

Whilst transverse cracking met the expectation of distribution set by LDF, longitudinal and corner cracking occurred at similar proportions. This led to an unexpected similar overall failure rate as shown in (Figure 6).

Slab Failure - Influence of Superelevation Further to initial observations regarding a good correlation between superelevation and high intensity of repairs, further analysis was undertaken to compare performance (in terms of cracking) in the superelevated and normal crossfall carriageway scenarios.

The analysis shown in the detailed graphs in 0 demonstrate the influence of superelevation on cracking, a summary of which follows:

• No correlation was demonstrated between superelevation and cracking in the following situations:

– Transverse cracking (slow and fast lanes)

– Longitudinal cracking (slow lane)

• However, longitudinal cracking in the fast lane of superelevated sections is approximately 8 times that of normal crossfall (as shown in Figure 7).

Subsequent investigation of this phenomenon revealed that high levels of failure did not occur in all superelevated areas, with some areas experiencing practically no failure.

It was found that the determining characteristic differentiating high failure from low failure is slab width - wide (~4.6 m) and narrow (~3.6 m), respectively (refer to Figure 8). The ability to draw a clear conclusion is caveated by the following:

• Wide slabs are located in two-lane sections whilst narrow slabs are located in three-lane sections,

• Wide slabs typically have 1.2 m wide integral shoulder whilst narrow slabs had a 3 m tied shoulder, and

• There are significantly more wide sections than narrow sections.

In any case, slab width does appear to be an aggravator, and is discussed in the following section on dimensional performance.

It is recommended that further studies be undertaken to determine whether similar correlations with superelevation have resulted in other

Figure 6 - Total cracking by lane position

Figure 7 - Longitudinal cracking in fast

lane by crossfall

Figure 8 - Longitudinal cracking of

superelevated slabs by width


areas. It is also recommended that possible causes of this high failure rate be investigated at the commencement of construction.

Dimensional Performance In 1984, the transverse joint system adopted by the DMR (now RMS) for undowelled PCP required a repeated 'random' spacing for sawn transverse contraction joints of 3.7- 4.3 - 4.6 - 4.0 m, a technique which was thought to minimise resonant vehicle responses (noise). This was an adaptation of the Californian system (at that time) which required 4.0 - 5.8 - 5.5 - 3.7 m spacings. The DMR, then concerned about possible maximum winter joint opening (aggregate interlock and load transfer), shortened the two longer California spacings to 4.3 m and 4.6 m.

Current RMS Standard Drawings place limits on slab length, width and shape factor – refer to Figure 9. These limits relate to critical stresses at transverse joints (and slow lane edges) and the restriction of maximum winter joint opening (1 mm) to maximise load transfer by aggregate interlock. Such current limits also mitigate the risk of excessive curling stresses (during curing) and principal strains (in service). When compared with current dimensional limits, much of the existing pavement is non-conforming.

Given the complete photometric catalogue of faults in the existing pavement, the design team was provided with a unique opportunity to compare the performance of slabs of different dimensions. From an analysis comparing failure rates with slab lengths and widths (refer to 0), and with the influence of crossfall direction removed, the following observations are made:

• Excessively-long slabs (> 4.2 m) performed similarly to conforming slabs,

• Excessively-wide slabs (> 4.3 m) experienced a notably higher failure rate (8x conforming slabs), and

• Excessively-long slabs outperformed excessively-wide slabs (for longitudinal and transverse cracking).

Transverse Skews (1:6) In the early 1990s, the RMS standard practice for transverse contraction joints changed to 1:10 skews (originally 1:6 from Californian practice) after observations that lower acute corner angles led to frequent corner breaks (ACI 2006).

Since this change occurred after the design of the existing site, P8 joints with 1:6 skews are present in the current pavements. A review of cracking performance of all existing slabs indicated corner cracking failure rates of 6% (normal crossfall) and 13% (superelevated) – when compared anecdotally with the performance of contemporary pavements, this analysis (refer 0) supports the adoption of 1:10 skews by RMS in the 1990s.

Figure 11 shows the existing 1:6 joint skews juxtaposed against the Upgrade widening featuring 1:10 joint skews.

Figure 9 - RMS PCP Trafficked Slab Dimensional Limits

Figure 10 - Corner cracking, 1:6 vs 1:10 skewed P8 joints, partial slab replacement and supplementary

joint stitching (top) (refer to for full figure)



DESIGN TRICKS AND TRAPS Field Confirmation Inspections Technology such as photometric surveys provides for ever-improving methods of desktop analysis. Obvious advantages over detailed field inspections include speed, safety and cost. Due to the high implied cost of repair work suggested by photometric surveys, the design team elected to undertake a field inspection. A 1.2 km segment of concrete pavement inspected was nominated as representative of the existing geometry and condition.

The intent of the survey was to verify the automated description of defects and confirm the subsequent recommended treatments. In addition to the verification aspect of this inspection, an assessment was carried out into the suitability of the fast lane pavement (once repaired) for widening by tying, dowelling and isolation.

Generally, the condition of the fast lane pavement slabs on both carriageways was found to be mostly consistent with the defects observed in the desktop study. The following additional issues however were not identified in the photometric survey:

• Changes in condition of some slabs (resulting from repair/deterioration),

• Corner stepping in P8 joints (at grades, justifying dedicated diamond grinding),

• Fine longitudinal cracks (not identified in the photometric survey),

• The use of cross-stitching in lieu of tiebars in some longitudinal joints (at time of construction),

• Variability of joint sealant type (preformed and silicone),

• The overall good condition of joint seals,

• Magnitude of crack widths (0.5 to 3.0 mm),

• Verification of cross-stitching performance,

• Coarse surface texture resembling an exposed aggregate finish, and

• Rocking of P8 joints under the movement of heavy vehicles.

The value of field inspections cannot be underestimated for the objective assessment of pavement condition and should be considered a necessary precursor to making repair prioritisation decisions, irrespective of the use of photometric surveys.

Repair Prioritisation and Optimisation RMS’ review of photometric survey data recommended that 2,625 slab replacements and corner repairs should be undertaken as a part of the Upgrade. Whilst initially envisioned to be undertaken as individual repairs occurring at night, this approach was unable to meet the delivery timeframe and cost expectations of the Upgrade.

Arcadis subsequently reassessed the required work in terms of prioritisation adopting the following principle for pavement repair - ‘the performance of widened pavements would be governed by the condition of the pavement to which they would be attached’. The application of this principle led to the elimination of slab replacements deemed not to be critical. The impact of this change to slab count, area and proposed night works is shown in Table 1. Furthermore, some proposed repairs were deemed not to be in keeping with the design brief - for example, joint resealing was considered to be a routine maintenance treatment.

Table 1– Comparison of slab replacements: Concept Design vs Arcadis Detailed Design

Design Stage

Slab Replacements

Total (night) Area m²

Concept 2,625* (1,579) 14,500

Detailed 1,442 (274) 22,207

* Includes recommended corner repairs (later converted to slab replacements)


Feedback from local RMS works staff indicated that the proposed corner repair method was unreliable, resulting in the conversion of these recommended repairs to partial or full slab replacements (depending on the severity). Proposed partial slab replacements were assessed to be of similar cost to full slab replacement and would likely have realised a shorter service life, and were therefore converted to full slab replacements.

Earlier observations identifying areas of high intensity slab failure led to the concept of consolidated slab replacement. This process involves a continuous machine-placed concrete paving run undertaken during the day in preference to a series of overnight individual slab replacements. As a rule, consolidated slab replacement was applied where the intensity of slab failure exceeded one in three for a sustained length. This concept provided the following benefits:

• Improved life cycle cost

• Reduction in duration of work

• Improved safety for workers

• Improved ride quality and surface finish

The concept of consolidated slab replacement presumes that slabs which are currently intact and located between failed slabs will imminently fail. This pre-emptive replacement action is considered to provide clear lifecycle advantages, consistent with the design brief. The use of consolidated slab replacement resulted in the additional replacement of apparently intact slabs leading to an increase in slab replacement of 8,151 m2 to a total of 22,207 m2.

The prioritisation and optimisation of identified repairs can result in an overall improved project outcome. Eliminating ineffective and inefficient options, and ensuring that only rehabilitation work that aligns with the project objectives is undertaken, will ensure that money is spent wisely. The use of consolidated slab replacement in high intensity failure areas has significant benefits to cost, finish and worker safety.

Download from Local Practitioners During the course of the design, a number of constructability, value engineering and risk workshops were conducted involving representatives from the RMS (client and asset management), Arcadis, verifier and sub-consultants. These exchanges are typically of high value and, despite a high proportion of time invested in them, are thought to significantly accelerate the detailed design through an iterative process.

Particular mention is warranted about the dedicated ‘download’ sessions at RMS’ Wyong Works Office with the District Works Manager and Maintenance Engineer. Tapping into local experience, which, in the case of the Works Manager extended as far back to very detailed recollections of original construction, allowed Arcadis to modify the design and contract documents in the following ways:

• The elimination of the RMS standard Corner Repair (no longer used locally due to poor performance),

• Interpret the geotechnical result with respect to source of materials in the median,

• Understand the likelihood and nature of subbase repairs (if required),

• Clarification of existing joint types, and

• Extents of stepping joints.

Local practitioners can provide valuable insight which can lead to optimisation of the design or clarification of unknown elements. Consultation with local practitioners should be considered a necessary step in the upgrade or rehabilitation of a road.

Aerial Correction of Photometric Survey The chainages reported in the photometric analysis did not correspond with project chainages which were based on survey. This was caused by inaccuracies associated with determination and measurement of chainages at and from start points. The degree of discrepancies ranged from 0.5 to 25.0 m.



In order to correct inaccuracies, Arcadis first considered a calibration exercise whereby fault mapping would be overlaid with orthorectified images from public digital databases, however these sources were not of sufficient resolution to confidently identify slabs by features. The following way forward was subsequently undertaken by the design team:

• Capture high resolution (35 mm) aerial photography (corridor-aligned)

• Orthorectify the high resolution aerial images

• Correct slab locations in the original photometric using orthorectified images

This procedure could however have been avoided by:

a. the use of accurate GPS location data, and/or

b. the establishment of a design control survey before the survey was undertaken.

Using the adopted methodology, the design team was able to confidently reposition location information of recommended repairs using high resolution orthorectified aerial imagery. Although recommended to ensure accurate GPS coordinates are obtained during the photometric analysis phase, the use of orthorectified high resolution images proved an effective means to obtain accurate GPS coordinates of slabs on site.

Mediating Joint Type with Multi-Criteria Analysis During the pavement options phase and constructability workshops a difference in opinion developed about the most suitable longitudinal joint type to be used for this project. This resulted in a significant level of discussion between RMS and Arcadis without resulting in a general agreement. To obtain final resolution, Arcadis employed the multi-criteria analysis technique to provide an objective decision. The tool employs three steps:

• Determine ranking criteria - identifying all influencing criteria then picking the five considered the most important.

• Determine criteria pairing - each criterion was ranked against the other using a score of 1-3 indicating how much the criteria is preferred over the other.

• Assignment of weighting criteria - ranks the relative importance of each criteria.

A weighted assessment was then undertaken where each possible solution was given a score between 1-5 for each criteria. The analysis was undertaken by individuals and finally as a group RMS-Arcadis exercise. The detailed consideration and deliberation of longitudinal joint types for widening works in this way allowed for a clear conclusion that a tied longitudinal joint solution would present the most reliable widening solution.

Sometimes it can be difficult to get multiple people to come to an agreement about an issue. The use of multi-criteria analysis in such occasions can assist in a final objective decision, saving time and allowing the project to keep on moving.

Figure 11 – Dedicated ‘spec run’ for aerial imagery

(Refer to Figure B 3 for full figure)

Figure 12 - Multi-Criteria Analysis Output Results (refer to Figure B 4 for full figure)

Score Weighted Score

5 70

3 42

Isolated Joint

Tied Joint

Criteria

A

Base slab thickness

(thicker using LDF1.0)

Pavement Option


Overcoming Thin Slabs and Variable Thickness The existing variable pavement thickness does not meet current minimum concrete pavement thickness standards and, given the requirement to match thickness, new slabs used to affect the widening will be similarly deficient. The impact of the thickness deficiency was disposed by a case presented in the Pavement Options Report relating to the low volume of heavy vehicles experienced by the fast lane.

To additionally minimise the risk presented by thin slabs, RMS proposed the use of ‘trapezoidal’ slabs wherein the thickness of the offside edge of widened pavement is set at 250 mm. Aside from the benefit arising from thickening, there is significant advantage that is gained during set-out whereby the offside edge of pavement now has a clearly defined levels which can be readily set-out using conventional survey techniques. Without this approach, the set-out of the offside edge would require the existing pavement edge to be exposed (then measured) in order to determine the thickness of pavement layers at any given point. The constructability of trapezoidal slabs will be assessed during construction.

The corollary potential application for trapezoidal slabs in widening projects is in the optimisation of costs for concrete widening whereby the new median widened pavement could be thinned toward the free edge in cases where the full thickness of the existing pavement is not required to meet the design loading. As opposed to the scenario where uniformly thick thinner widening slabs are rejected as options, this approach would eliminate the need for a longitudinal interface drain thereby improving the viability of the approach.

Trapezoidal shaped slabs may be an effective means to overcome variable and non-conforming thickness during widening. There is also potential for to use trapezoidal slabs to provide an overall thinner slab than the existing, allowing for a reduction in materials.

Widening Methodology Default RMS standard drawings for maintenance and practice adopted from lessons on the M2 widening and F3 Berowra, suggested that, in preparation for widening, the existing concrete shoulder be cut-back by a nominal 0.5 m from the existing pavement edge to avoid the longitudinal joint coinciding with a wheel path and to limit the impact of edge drop-off.

For this project the Arcadis design team proposed that the 0.5 m nominal cut-back could be reduced to 0.3 m assuming the contractor could demonstrate the reduced cut-back appropriately addressed the impacts of edge drop-off and that any uncertainty regarding edge support was resolved. Reducing the cut-back to 0.3 m also maximised the residual slab width and reduced the volume of concrete required to widen the pavement. The position of the joint surface with respect to wheel paths was not considered critical because tied longitudinal joints are considered durable under light vehicle traffic (fast lane).

The cut-back technique and widening methodology was therefore developed by sawcutting 0.3 m from the existing fast lane pavement edge where possible ensuring the following:

• Minimum widened width to be 1.0 m (where the resultant slab does not meet Shape Factor requirements, PCP-R will be considered)

• Avoid locating the joint in the wheel path (transitions exempted)

• Comply with the standard RMS Slab Dimensional Limits

• Saw cut 0.1 m from the existing subbase

• Prepare subgrade (including the removal of any existing trench drains) for the widening

• Machine-place subbase and base to match the existing thickness of the adjacent concrete base

Reducing the cut-back by 200 mm over the length of the project is expected to save money, reduce wastage of concrete needing to be removed then replaced and still provide the desired outcomes of reducing edge drop-off.



Variable Widening Width and Tapers As a result of the non-parallel alignment of the Upgrade (see later section “Realign at your Peril”) and in order to optimise the costs and slab dimensional performance, new median slabs varied in width. This lead to a requirement to develop an appropriate ‘taper’ detail that would simultaneously minimise the extent of hand-placed concrete slabs as well as not exacerbate the existing 1:6 joint skew in slabs which we retained.

Noting the sensitivity of slabs to increasing corner acuteness (2% stress increase for every 1º, ACI 2006), a 1:60 taper was adopted where transitions occurred between wide and narrow slab widenings so as to reduce the potential for corner cracking caused by tapering joints. Arcadis determined that slab width changes occurred in 36 locations where slab width changes were required. Offsets varied between 100 mm and 1000 mm.

Taking into account the combined effect of hand placed slabs, direction of taper, absolute offset required and the ability to reinforce significantly stepped joints, a criterion of 600 mm (maximum) was determine for the arbitration between tapered and stepped joints. This resulted in five locations requiring discretely stepped joints (bounded by P7 joints) and 31 locations requiring tapered joints. The tapers specified were either 1:60 or 1:6 depending upon the direction of the taper – transition lengths where tapers diverged toward the median (in the direction of travel) could be limited in length due to the improvement of corner angles. Refer to Figure 14

Good Client-Designer Working Relationship Client design briefs don’t always communicate the true intent of a project. The success of this design was in part credited to a client team which understood the true intent of the project as it applied to reinterpretation of the Brief regarding rehabilitation philosophy, specifically by:

a. ensuring Arcadis targeted an output which was focussed on adding capacity rather than rebuilding, and

b. providing clarity between the choice of best practice and optimised compromise practice

For best project outcomes, it is essential that the designers try to understand the intent of the project rather than only take the requirements from the Brief. Where it is identified that a departure from the Brief may deliver project outcomes more in line with the project intent, they should be discussed with the client.

Figure 13 – Tapered joint/slab detail (hand placed)


Realign at your Peril The existing pavement consists of 3 m shoulders, however in cuts this includes an untrafficable Type SH gutter which effectively reduces the trafficable shoulder widths to a non-compliant width of 2 m. The concept design proposed a ‘meandering’ control line compared with the existing. This created a number of undesirable implications as listed in Table 2 (an extract of )

Arcadis put forward a case which outlined the disadvantages listed in Table 2, however the case was not successful and the meandering control line was retained. A stronger case may have averted significant design consternation and additional costs which, in terms of material costs alone, was in the order of $350,000 for additional concrete and granular materials. This estimate will worsen with the inclusion of costs arising from changing paver widths, additional design work, additional earthworks and the elevation of risks of errors during construction.

Due to the problems identified, it is recommended that future concrete widenings adopt a control line which is parallel to the existing. This can be achieved by replacing the existing gutter or carefully considering the implications of accepting a non-conforming gutter.

Separation of Night and Day Works At the start of the detailed design phase, the project was initially envisioned as multiple contracts, one for the widening and one for the existing pavement rehabilitation. The idea was that a contractor, likely more specialised in the pavement rehabilitation, will undertake night work slab repairs prior to the widening work commencing.

As the design progressed and the idea of consolidated and day work repairs developed, the works became intrinsically linked. It soon became apparent that potential benefits existed for merging the two contracts including:

• A shorter overall duration of construction works could be gained if the night and day works were done in parallel. This would require the barriers used during the day to be removed temporarily while works took place at night.

• Enable the contractor to identify additional night works that could be undertaken during the day or additional areas of individual slab replacement to be undertaken at night. Encouragement for the contractors to identify such areas would need to be provided.

• Ensure one contractor takes ownership of all works related to the project, thereby potentially reducing disagreements about warranty and any potential causes of early pavement failure.

• Reducing the reliance on the assumed traffic staging and pavement design of widening works, which, at the time of an early works contract, would still be in development.

Potential disadvantages of combining the widening and repair work contracts were identified as follows:

• A contractor not as specialised in rehabilitation may be chosen

• If the rehabilitation works was sub-contracted, the main contractor would likely charge an additional fee to manage the sub-contractor, resulting in a higher overall cost than if done separately.

• The end construction date may be pushed back as no rehabilitation work could be done until the main contract was awarded. This could be offset if night time rehabilitation work could be undertaken in parallel to the main works.

• The project had been communicated to members of the public as separate works.

Table 2 - Impacts of a ‘meandering’ control line



When a widening project contains some pavement rehabilitation, there are some potential advantages to be gained from delivering the project as one contract instead of splitting it into two. Most significant of which is a shorter overall construction time.

Traffic Staging - Interrelationship with Design One of the surprising key influencers on the pavement design was traffic staging. Whether a required repair was undertaken as a compromised individual night work repair or as a best practice daytime repair was based on whether it made sense from not only a cost perspective but also a traffic staging perspective. Some locations, the assumed traffic staging methodology wouldn’t allow repairs to take place during the day due to geometric restrictions. Conversely, some individual repairs, that would have otherwise been executed as compromise practice at night, were able to be undertaken as best practice repairs during the day based on the assumed traffic staging.

The staging also involved the use of temporary pavement in some areas. Rather than requiring the temporary pavement to be removed entirely, there was opportunity identified for the temporary pavement to be trimmed back to form part of the final shoulder.

Late in the design, a likely construction scenario was identified that would result in the temporary misalignment of transverse P8 joints between newly widened pavements the adjacent existing slabs, many of which were to be replaced after widening using the consolidated slab replacement technique. In consideration of the low early strength of concrete in the widened pavement, concerns were raised that a reflection crack may form in the new pavement coinciding with the location of the joint in the existing slab. To mitigate this risk by affecting a positive interruption of the bond between the temporarily mismatched joint locations, a new detail was developed using a metal debonding sheet at the overlapped zone.

A key difficulty of this is that the project was delivered as a part of a ‘Design Only’ contract meaning the final traffic staging would be determined by the contractor. It was therefore essential to ensure that a reasonable traffic staging was assumed, the influence of the traffic staging on the design was communicated clearly in the drawings and specification and that appropriate mechanisms were in place to allow the contractor to improve upon the design if their traffic staging allows it.

The risks associated with the contractor adopting a different construction staging methodology would be eliminated if the project was delivered as a ‘design and construct’ contract. This would have allowed the designers to work with the contractor to explore more avenues of optimisation and reduced the risk of miscommunication.

During widening of concrete pavements, especially those involving some rehabilitation works, special consideration needs to be given to the influence of the traffic staging on the design. Where it is identified that they are interlinked, it is essential that a reasonable potential traffic staging is assumed. Appropriate mechanisms need to be set up to allow the contractor to modify the design, where not detrimental to the project, based on the actual construction staging that will be used. Additionally, issues affecting the pavement as a result of the way it is assumed to be staged, such as the temporary misalignment of joints, should be considered and dealt with during the design. To overcome the risks associated with an inaccurate staging being assumed, consideration should be given to the delivery of projects as a ‘design and construct’ contract.

Slab Dimensional Constraints With the choice to affect the widening using a tied longitudinal joint, the existing variable slab length (when coupled with the requirement for matched P8 transverse joints and the issue of relative meandering control lines), imposed additional limitations of the range of slab widths selected for widening. The correction of skew was implemented, however, constrained variable slab length presented a greater challenge. Slabs widths for widening were varied where possible to ensure compliance with slab dimensional limits, however the requirement for sustained width over reasonable paving lengths led to occasional non-conformances. The risk of performance impacts arising from these non-conformances was disposed by the addition of mesh reinforcement to some slabs and the presentation of data demonstration excess design capacity (predominantly light traffic).


Diamond Grinding Neither the design brief nor the Concept Design considered the use of diamond grinding in any capacity. Indeed, the only mention of diamond grinding was in the context of one verification comment. However, the potential use of diamond grinding was identified during the Start-up Meeting as an obvious treatment for poor megatexture likely to arise from isolated slab replacements. The use of diamond grinding was also thought to be the default treatment for the removal of linemarking and rectification of stepped slab joints. Typical roughness of the existing site is between 50 and 70 NAASRA roughness counts.

It was later concluded that diamond grinding was an undesirable treatment for isolated removal of thermoplastic linemarking and that roughness intervention levels had not yet been met in significant extents of the existing pavement. However, in the absence of a suitable alternative for linemarking rectification, in consideration of the supplementary benefits provided by grinding and upon of a detailed estimate for grinding (less than 5% of project budget), it was decided to apply the diamond grinding treatment to the full trafficked width of the pavement after completion of the repairs.

Due to lack of cost-effective and well performing alternative treatments, diamond grinding should be considered the default treatment for linemarking rectification and improving megatexture for isolated pavement rehabilitation.

Pitfalls of Crowning Aquaplaning risk (outside current conformance) was identified in a number of locations. The new widened pavement would extend flow-paths and exacerbate the water film depth, thus increasing aquaplaning risk. This risk was mitigated by the design of a crowned hinged joint between Lane 2 and Lane 3 (new fast lane).

Whilst mitigating the risk of aquaplaning, the crowned joint constrained the position of the new longitudinal joint to the lane line. As the position of the crowned longitudinal joint did not align with areas of adjacent widening (where crowning was not required), the need for a tapered or P7d ‘stepped’ transition was necessitated, to avoid the risk crack induction and propagation. This effectively interrupts the ability of the contractor to undertake a continuous fixed-width machine-placed paving run. The inclusion of a crowned (widened) caused a pinch point in construction staging which reduced the nearside temporary shoulder width below desirable levels.

An alternative means to mitigate the aquaplaning risk would be to groove the pavement. Grooving increases the pavement texture depth causing a reduction in water film depth. RMS commonly provide an arbitrary value for all concrete and asphalt surfaces, which does not take into account dramatic actual differences between surfaces, thus excluding the use of grooving. Calculations using Austroads values for texture depth demonstrate that grooving provides a similar effectiveness in reducing aquaplaning. Additionally, the use of grooving as an alternative means was made difficult due to the commitment in earlier design stages to crowning despite calculations.

The use of crowning in concrete pavement can be problematic if all consequences are not considered. For projects using concrete pavements, especially widenings, the use of grooving instead of crowning should be considered. More flexibility in the project briefs to use realistic texture depths for grooved pavements should be given.



SUMMARY OF OUTCOMES As part of detailed design for the Upgrade, Arcadis undertook the analysis of an unprecedented amount of data relating to the existing condition of the pavements from which the following observations are made in relation to past performance:

• Superelevated fast lane slabs experienced longitudinal cracking eight times higher than the slow lane,

• Slabs of width exceeding current standards experienced a significant increase in failure when compared with slabs exceeding maximum length, and

• Against expectations, longitudinal and corner cracking levels in the fast and slow lanes were similar.

Following the construction of RMS’ first concrete ‘modern’ pavement in 1975, and with approximately 22M square meters of concrete pavement asset under management, much of which is exceeding 30 years in service, NSW is moving from a period characterised as ‘building’ to one of ‘maintenance’. With the need to upgrade capacity of key highways, it is timely to document lessons acquired during the course of this design which are not currently expressly documented by RMS or Austroads. The lessons (‘tricks’) reviewed in this papers are:

• The analysis of slab failure frequency (intensity) is a necessary tool for optimisation of design

• Preliminary condition assessment by photometric surveys is beneficial for the collection of condition data, however it is important to supplement or ‘calibrate’ these remote methods with field inspections

• It is important to understand whether the design brief asks for an upgrade of capacity or rehabilitation of condition, and the repair prioritisation be undertaken accordingly.

• Consolidated slab replacement can affect reduced life cycle costs, reduced construction durations, improved safety for workers and improved ride quality and surface finish

• Conversations and workshops with practitioners familiar with maintenance of the existing asset and/or its original construction can yield valuable observations that are not captured in work-as-executed drawings or clarified by geotechnical investigations

• Aerial surveys are an effective means to correct GPS inaccuracies in photometric surveys

• Multi-criteria analysis is a useful quantitative tool to assess the relative value of design options

• Whilst the P2d joint and interlayer drainage considerations constrain the widening pavement thickness to ‘matched’, accurate design capacity may be determined using accurate LDFs on a per-lane basis.

• Trapezoidal edge thickening of slabs may be an effective means to overcome variable and non-conforming thickness during widening.

• A good Client-Designer working relationship is essential for re-/interpretation of the brief

The lessons learned during this design which that potentially had a negative consequence were:

• The assignment a new design control line which is not parallel to existing, should be considered carefully

• Night and day works can be executed interstitially and should not designed as separate design lots

• The basing of normative repair designation on informative staging, may result in delivery conflicts

• Existing variable slab length can result in widening design constraints leading to non-conformances

• The use of grinding to affect removal of thermoplastic linemarking is potentially unjustified

• The use of crowning in concrete pavement can be problematic if all consequences are not considered.


RECOMMENDED FUTURE WORK Whilst this paper presents insight into some of the more striking discoveries and lessons that surfaced during the development of the M1 Kariong to Somersby Upgrade detailed design, it should be emphasised that some of the conclusions drawn here, particularly in Past Performance, are preliminary and deserve to be reviewed in greater detail. Other projects built to similar standards include Hume Highway Tumblong, Hume Highway Marulan, Hume Highway Berrima and M1 Pacific Motorway Wyong.

It is recommended that:

• Further studies be undertaken to determine whether similar correlations with superelevation exist.

• Possible formation issues are investigated at the commencement of construction into the cause of the high failure rates demonstrated in the superelevated sections of existing fast lane, and

• RMS develop a ‘Concrete Pavement Widening’ guide that addresses issues unique to widening and that are not covered by the existing Standard Drawings and Maintenance Drawings.

REFERENCES ACI 2006 - ACI Committee 325 2006:4 and Ayton and Donald, Roads 96: 18th ARRB Transport Research Conference 1996 Victoria, NSW

CACA 1982 - Technical Note TN 47 Joints in Concrete Pavements June 1982 J. Hodgkinson



APPENDIX A - SLAB FAILURE ANALYSIS

Figure A 1 - Slow Lane Slab Failure

Figure A 2 - Fast Lane Slab Failure


Figure A 3 - Normal Crossfall Slabs Failure by Width

Figure A 4 - Superelevated Slabs Failure by Width



Figure A 5 - Slab Failure by Length

Figure A 6 - Slab Failure by Shape Factor


APPENDIX B - ALL OTHER FIGURES

Figure B 1 - Sample photometric survey output by RadarPortal

Figure B 2 - Extended extract from detailed design showing corner cracking, 1:6 vs 1:10 skewed P8 joints, partial slab replacement and supplementary joint stitching (top)



Figure B 3 - Detailed ‘spec run’ for aerial Imagery


Table B 1 - Impacts of ‘meandering’ control line

Problem Impact

Variable width of new widening into the median

• Frequent changes in paver set up

• Complications in median due to stepped edge

• Increased costs due to wider slabs

• Complicated set out

Longitudinal joints no longer coinciding with lane lines

• Potential joints in wheel path

• Existing slow lane joint is inside joint is inside the slow lane line and therefore closer to heavy vehicle wheel path

Existing lane lines different from new lane lines • Elevated driver distraction arising from the intrusion of erased thermoplastic markings

Figure B 4 - Multi-Criteria Analysis Output Results

Score Weighted Score Score Weighted

Score Score Weighted Score Score Weighted

Score Score Weighted Score Score Weighted

Score

5 70 1 11 1 3 5 15 1 1 3 0 100

3 42 5 55 5 15 2 6 5 5 5 0 123

5 70 2 22 2 6 3 9 3 3 3 0 110

Total Score

Isolated Joint

Tied Joint

Dowelled Joint

Criteria

A B C D F

Base slab thickness

(thicker using LDF1.0)

Longitudinal joint position

less constrained

No subgrade and edge beams

Influence of adjacent slab on

new fast lane (short term, as it impacts staging)

Standard practice

(experience)

Interface drains required

E

0

Pavement Option

Weighting 14 11 3 3 1

Documents

Concrete Pavement Upgrades - Tricks and Traps Papers/Paper 22... · rectification or justifying slab replacement. ... of the frequency of slab failures along the Upgrade. ... Concrete