Manual Wirtgen

8/22/2019 Manual Wirtgen

1/369

Cold Recycling

Wirtgen Cold RecyclingTechnology


2/369


3/369

Cold Recycling

Wirtgen Cold RecyclingTechnology


4/369


5/369

Acknowledgements

This rst Edition o the Wirtgen Cold RecyclingTechnology manual was compiled by a team ospecialists with extensive experience in all aspectso pavement rehabilitation, especially those relat-ing to the reuse o material rom existing roadpavements.

The team included Engineers rom LoudonInternational who have assisted Wirtgen and theircustomers in the application o cold recyclingtechnology or nearly twenty years. In recognitiono rapid advances being made in the specialisedarena o pavement engineering, an invitation to

join the team was extended to selected academicsrom some leading universities, especially Stel-lenbosch University. Their invaluable contributions

are evident throughout the manual, particularly inthose chapters concerned with pavement designand stabilising agents. In addition, engineers romWirtgen GmbH provided valuable guidance inaddressing the shortcomings o this publicationspredecessor, the Second Edition o the Wirtgen

Cold Recycling Manual and concerns previouslyvoiced by customers and eld engineers havebeen addressed in this new publication.

Wirtgen GmbH are grateul to all who contributedto this manual and invite eedback rom those whoread it. Any comments will be welcomed, regard-less o the nature o such comments.These should be sent to [email protected]


6/369

Preace

For the last twenty years, Wirtgen has been atthe oreront o the development o cold recyclingtechnology. During this time, both the technologyitsel and the machines that carry out the recyclingwork have evolved rom simple beginnings to thecurrent status where cold recycling is recognised

worldwide as a normal process or constructingpavement layers, particularly or rehabilitatingdistressed pavements.

Cold recycling technology is currently employedto construct all types o pavements, ranging romminor access roads to major multi-lane highways.Where a pavement is in a distressed state, thereis always an option to recycle the existing materialand reap the benets in terms o lower construc-tion costs, improved durability (service lie) and,

equally important, a signicant reduction in thenegative impact that construction has on theenvironment.

The cold recycling process has been success-ully used to rehabilitate and / or upgrade manythousands o kilometres o roads during thepast twenty years. The list o projects on whichWirtgen recyclers have been deployed worldwideis exhaustive and covers all climatic regions on all

continents (except Antarctica where there are noroads). Pavements in both the Developed and Un-developed Worlds are increasingly being recycledas a solution to the deteriorating condition o theirroad networks.

Experience gained rom these projects has allowedWirtgen to actively push the barriers o technol-ogy by investing in research and developmentand trialling new ideas and concepts (e.g. bitumenstabilisation). These developments have all been obenet to the global industry.

This 1st edition o Wirtgen Cold RecyclingTechnology is a compilation o lessons learnedover the past twenty years. It includes everythingthat is needed to understand the technology,what it is, where it can be applied and how todesign pavements that incorporate cold recycledmaterials. It is particularly useul or those with littleexperience in recycling and wish to learn aboutthe technology. However, it is also useul or themore experienced practitioner since it includes

advances achieved rom the most recent researcheorts, especially those in the exciting eld o bitu-men stabilisation.In this regard, the technology has evolved romrecycling materials that include mixtures o granu-lar, cemented and asphalt materials to recyclingmaterial comprised entirely o recycled asphaltpavement (RAP) material.

In publishing this new manual, Wirtgen GmbH wish

to share their knowledge and understanding ocold recycling, not only with their customers whohave provided many o the experiences, but alsowith the global road construction community, inthe belie that sharing is the path to advancementand a brighter uture or all.


7/369

Glossary o abbreviations

AADT Average annual daily trac (Appendix 2)AASHTO American association o state highway and transportation ocialsADE Average daily equivalent trac (Appendix 2)BSM Bitumen stabilised material (Chapter 4)BSM-emulsion BSM made with bitumen emulsion (Section 4.1.4)BSM-oam BSM made with oamed bitumen (Section 4.1.4)

CIR Cold in place recycling (Chapter 6)CBR Caliornia bearing ratioCTB Cement treated baseDCP Dynamic cone penetrometer (Section 2.5.4)ELTS Eective long term stiness (Section 2.6.4)EMC Equilibrium moisture contentESAL Equivalent standard axle load (80 kN) (Appendix 2)FWD Falling weight defectometer (Section 2.4.1)GCS Graded crushed stone materialHMA Hot mixed asphaltHVS Heavy vehicle simulator

ITS Indirect tensile strength (Appendix 1)LTPP Long term pavement perormanceMDD Maximum dry densityOMC Optimum moisture contentPen Penetration grade (bitumen standard test)PMS Pavement management systemPI Plasticity indexPN Pavement number (Section 2.6.4)PWoC Present worth o cost (Appendix 4)RAP Reclaimed asphalt pavement (asphalt millings)

SN Structural number (Section 2.6.3)TSR Tensile strength retained (Section 4.3.11)UCS Unconned compressive strength (Appendix 1)UTFC Ultra-thin riction course (asphalt suracing layer)WAM Warm mix asphalt


8/369

Content

1 Introduction 10

1 Road Pavements 15

1.1 Pavement structures 16

1.2 Pavement components 18

1.2.1 Suracing 18

1.2.2 Structural layers 19

1.2.3 Subgrade 21

1.3 Primary considerations or the pavement structure 22

1.3.1 Environmental conditions 23

1.3.2 Traic loading 25

1.4 Pavement distress mechanisms 26

1.4.1 Advanced pavement distress 26

1.5 Pavement maintenance and structural rehabilitation 28

1.6 Rehabilitation options 30

1.6.1 Surace rehabilitation 31

1.6.2 Structural rehabilitation 34

2 Pavement rehabilitation 38

2.1 General 41

2.2 Pavement rehabilitation: investigation and design procedure 42

2.3 STEP 1: Data acquisition / process available inormation 44

2.3.1 Inormation on the existing pavement (historical inormation) 452.3.2 Design traic 46

2.4 STEP 2: Preliminary investigations 48

2.4.1 Determination o uniorm sections 49

2.4.2 Visual inspection 52

2.4.3 Reassessment o uniorm sections 54

2.5 STEP 3: Detailed investigations 55

2.5.1 Excavating test pits 55

2.5.2 Laboratory testing 562.5.3 Extracting core specimens 57


9/369

2.5.4 Dynamic cone penetrometer (DCP) probes 58

2.5.5 Analysis o delection measurements 60

2.5.6 Rut depth measurements 60

2.5.7 Synthesis o all available data 61

2.6 STEP 4: Preliminary pavement rehabilitation design options 62

2.6.1 Pavement design approach 622.6.2 Catalogue design methods 63

2.6.3 Structural number method 63

2.6.4 Pavement number method 64

2.6.5 Mechanistic design methods 66

2.6.6 Delection based methods 67

2.6.7 Summary o pavement design approaches 67

2.7 STEP 5: Laboratory mix design 68

2.8 STEP 6: Finalise pavement design options 702.9 STEP 7: Economic analyses 71

3 Cold recycling 73

3.1 General 75

3.2 The cold recycling process 77

3.2.1 In-plant recycling 78

3.2.2 In-place recycling 79

3.3 In-place recycling machines 84

3.4 Cold recycling applications 90

3.4.1 100% RAP recycling 93

3.4.2 Blend o RAP / Granular material 94

3.5 Beneits o cold recycling 97

3.6 Applicability o the cold recycling process 98

4 Stabilising agents 100

4.1 Types o stabilisation agents 103

4.1.1 General 1034.1.2 Material behaviour 104


10/369

4.1.3 Cementitious stabilising agents 105

4.1.4 Bitumen stabilising agents 106

4.1.5 Summary o dierent stabilising agents 109

4.2 Stabilising with cement 110

4.2.1 General 110

4.2.2 Factors aecting strength 1104.2.3 Cracking o cement stabilised layers 111

4.2.4 Surace crushing 114

4.2.5 Durability concerns 115

4.2.6 Working with cement 116

4.2.7 Early traicking 120

4.2.8 Key eatures o cement stabilised materials 121

4.3 Stabilising with bitumen 123

4.3.1 Overview 123

4.3.2 BSM Distress Mechanisms 126

4.3.3 Primary determinants o BSM perormance 127

4.3.4 Material to be stabilised with bitumen 128

4.3.5 Bitumen stabilising agents 136

4.3.6 Active iller 140

4.3.7 Water quality 141

4.3.8 Mix design procedure 142

4.3.9 Classiication o BSMs 144

4.3.10 Working with BSMs 146

4.3.11 Mechanical tests 152

4.3.12 Pavement design approaches or BSMs 154

4.4 Summary: Advantages and disadvantages o cement and bitumen stabilising agents 160

5 Recycling Solutions 163

5.1 Guidelines or recycling dierent pavements 165

5.1.1 Lightly traicked roads (structural capacity: 0.3 million ESALs) 166

5.1.2 Low volume roads (structural capacity: 1 million ESALs) 1685.1.3 Secondary rural roads (structural capacity: 3 million ESALs) 170

Content


11/369

5.1.4 Main rural roads (structural capacity: 10 million ESALs) 172

5.1.5 Interurban highways (structural capacity: 30 million ESALs) 174

5.1.6 Major multi-lane highways (structural capacity: 100 million ESALs) 176

5.2 Alternatives or pavement rehabilitation 178

5.2.1 Existing pavement 180

5.2.2 Rehabilitation requirements 1815.2.3 Rehabilitation options 182

5.2.4 Maintenance requirements 190

5.2.5 Construction & maintenance costs 192

5.2.6 Energy consumption 195

5.2.7 Relevant comments 199

6 Recycling 100% reclaimed asphalt pavement (RAP) material 201

6.1 RAP material 203

6.1.1 Bitumen binder 203

6.1.2 Grading o the RAP material 205

6.2 Uses or cold recycled RAP material 206

6.2.1 Untreated RAP material 206

6.2.2 RAP material treated with cement 207

6.2.3 RAP material treated with bitumen emulsion 207

6.2.4 RAP material treated with oamed bitumen 211

Bibliography 214

Appendix 1 Laboratory procedures or stabilised materials (mix designs) 218

Appendix 2 Determining structural capacity rom trac inormation 307

Appendix 3 Guidelines or compiling specications or recycling projects 320

Appendix 4 The principles o economic analysis 355


12/369

The Wirtgen Cold Recycling Manual was rstpublished in 1998, in English. Due to advances inrecycling technology, it was necessary to rewritethe manual ater six years and, accordingly, theSecond Edition was published in 2004.The Second Edition was well received; within a

couple o years it had been translated into a dozendierent languages and, by the end o 2009, morethan 50,000 printed copies had been distributedworldwide with at least the same number down-loaded rom the www.wirtgen.de website.

As with the First Edition, the Second Edition at-tracted considerable attention with an increasingnumber o reports, conerence papers and othertechnical publications making reerence to themanual. It would appear that the Second Edi-

tion o the Wirtgen Cold Recycling Manual hassuccessully built on the reputation established byits predecessor as the primary reerence book orcold recycling technology.

Almost a decade has now passed since theSecond Edition was published. During this time,interest in recycling has intensied, refected bythe increasing number o recycling machines thatare sold around the world every year. This has

encouraged the research and development teamat Wirtgen headquarters to continue to improvethe machines they manuacture, based on eed-back received rom their global network o serviceengineers and customers. Such an increase ineld activity succeeded in attracting interest romthe academic community with the result that coldrecycling technology took a giant step orwardthanks to their research eorts. Since 2004, muchgroundbreaking research work has been carriedout, especially concerning bitumen stabilisation, a

technology that is ideally suited to cold recycling.

These developments and improvements eectivelyoutdated some sections o the Second Edition.This, coupled with the reerence document sta-tus enjoyed by the Manual warranted a thoroughreview and update o the contents, a process thathighlighted the need or a total rewrite. In addition,

the inormation that needs to be included in theManual has grown exponentially and is now toomuch or a single publication. Accordingly, thedecision was taken to replace the manual with twopublications:

Wirtgen Cold Recycling Technology that o-cuses on aspects o pavement theory anddesign that are relevant to cold recycling.Included is a detailed explanation o coldrecycling and is particularly useul or engineers

involved with material utilization and pavementdesign.

Wirtgen Cold Recycling Application thatcovers the practical aspects o applying thetechnology. This separate publication describesthe various construction processes that can beused or cold recycling and is useul or practi-tioners and eld engineers

As with the previous Cold Recycling Manuals,these new publications are ocused on recyclingcold material or use in fexible pavements. Theydo not include recycling hot material, nor do theyconsider rigid (concrete) pavements, both beingseparate specialist elds. In addition, they do notinclude hal-warm and warm asphalt. Foamedbitumen technology is ideally suited to such mixesbut adaptations to mix evaluations and pavementdesign are required and are not covered in thismanual.

Introduction


13/36910 //11

This 1st Edition o Wirtgen Cold RecyclingTechnology includes the ollowing:

Chapter 1 provides an overview o pavements.The composition o pavement structures is ex-plained along with a brie description o the main

actors infuencing the selection o the variousmaterials used to construct the dierent layers andhow they behave (and deteriorate) when subjectedto dynamic wheel loads. This leads on to the sub-

ject o pavement rehabilitation and introduces theconcept o cold recycling, both in situ and in plant.

Chapter 2 ocuses on pavement rehabilitation anddescribes the engineering input required to ormu-late a suitable design, particularly those aspectsthat are relevant or cold recycling. Pavement

investigations, material analyses and pavementdesigns are all covered in detail in a seven stepprocedure culminating with a section on economicanalyses to assist in evaluating the nancial meritso dierent rehabilitation options.

Chapter 3 explains cold recycling and the variousapplications that can be considered, both in situand in plant. The range o Wirtgen recyclingmachines is introduced along with an explanation

o the type o recycling best suited to eachmachine. Also included is a summary o thebenets to accrue rom adopting a cold recyclingapproach and the suitability o the process orconstructing pavement layers, or both new roadsand or rehabilitating distressed pavements.

Chapter 4 ocuses on the stabilising agents thatare normally applied in the cold recycling process.Mix and pavement design procedures or bothcementitious and bituminous stabilising agents are

explained in detailed. Recent developments in theeld o bitumen stabilised materials (BSMs) have

been included. These developments have movedthe technology orward rom that covered in theSecond Edition o the Wirtgen Cold RecyclingManual, triggering the need or a rewrite.

Chapter 5, entitled Recycling Solutions, uses a

catalogue design ormat to show a series o typi-cal pavement structures suitable or rehabilitationby recycling, including both cement and bitumenstabilisation options. Six trac classes between300,000 and 100 million equivalent standard axleloads (ESALs) are included, each with dierentsubgrade support conditions that would normallybe encountered or such a class. This is ollowedby an example o dierent options that can beused to rehabilitate a specic pavement with astructural capacity requirement o 20 million

ESALs. An existing (distressed) pavementstructure is used to select our dierent rehabilita-tion solutions as well as the maintenance require-ments or each over a 20-year service lie, togetherwith the relevant rehabilitation requirement ater20 years. The whole-o-lie cost or each option isthen evaluated using dierent discount rates.In addition, the energy consumed by all con-struction activities during the service lie o eachrehabilitation option is evaluated.

Chapter 6 is ocused on reusing 100% reclaimedasphalt pavement (RAP) material in a cold recyclingprocess. This subject was not covered in any detailin the previous manuals and has been includedto address the increasing interest being shownworldwide in recycling this specic type o materialusing a cold process. (The in situ recycling pro-cess is known in some countries as cold in placerecycling (CIR) or partial depth reclamation).

A list o relevant Bibliography is included immedi-ately ater Chapter 6.


14/369

The our appendices contain a host o additionalinormation, all relevant to cold recycling, but toinclude them in the chapters would make themanual cumbersome.

Appendix 1 describes the laboratory procedures

or stabilised materials (mix designs). This is ol-lowed by a schedule o equipment required orcarrying out the laboratory work.

Appendix 2 describes the methodology used todetermine the correct pavement design criteria(structural capacity requirement) rom trac data.

Appendix 3 includes guidelines or compilingappropriate construction specications or coldrecycling projects.

Appendix 4 provides useul background inorma-tion or economic analyses.

Pavement rehabilitation is becoming more impor-tant as the overall condition o the worlds roadinrastructure continues to deteriorate and many

countries are acing a steady decline in the stand-ard o their ageing road network.

Ever increasing maintenance and rehabilitationeorts required to retain acceptable levelso service place tremendous pressures on national

budgets. This situation is exacerbated by the glob-al pattern o growing trac volumes compoundedby increasing axle loads and tyre pressures, ac-tors that all contribute to pavement deterioration.This downward spiral can only be addressed bya massive increase in road budgets coupled withinnovation in the eld o pavement engineering.

Since ew road budgets are increasing in realterms, ocus is being placed on innovation toachieve more with relatively less expenditure.

Recycling clearly alls into this category andrecords show that the number o lane-kilometreso distressed pavement being rehabilitated usingthe cold recycling process is increasing annually.Simple economics is the main reason or this phe-nomenon as it refects the cost eectivenesso the process.


15/36912 //13


16/369


17/36914 //15

1.1 Pavement structures 16

1.2 Pavement components 18

1.2.1 Suracing 18

1.2.2 Structural layers 19

1.2.3 Subgrade 21

1.3 Primary considerations or the pavement structure 22

1.3.1 Environmental conditions 23

1.3.2 Traic loading 25

1.4 Pavement distress mechanisms 26

1.4.1 Advanced pavement distress 26

1.5 Pavement maintenance and structural rehabilitation 28

1.6 Rehabilitation options 30

1.6.1 Surace rehabilitation 31

1.6.2 Structural rehabilitation 34

1 Road Pavements


18/369

Road pavements comprise three basic

components:

Suracing: The riding surace which is usuallythe only part o a road that is visible.

Structural layers: The load spreading layers,

consisting o dierent materials, oten extendingto depths in excess o one metre.

Subgrade: The existing earth upon which theroad is built.

Subgrades are usually o relatively low bearingcapacity and cannot carry trac loading directly,so protective overlying layers are needed. Thepurpose o the suracing is predominantly unc-tional providing an all weather riding surace with

properties o comort, saety and environmentalconsideration (e.g. low noise). The structural layersdistribute the high intensity surace loads gener-ated by trac over a wider area o subgrade, asillustrated in the gure below.

The individual layers in a pavement structure varyin composition (material type) and thickness.Those layers closest to the surace are construct-ed using high-strength materials (e.g. hot-mixasphalt) to accommodate the higher stresses.Individual asphalt layers seldom exceed 100 mmthickness. As the load is distributed over a widerarea in the lower layers, the level o stress reducesand can be carried by poorer quality materials(e.g. natural gravels or lightly cemented materials).Consequently, the materials in the lower layers are

1.1 Pavement structures

Suracing

Structural layers

Subgrade

Wheel load

Contact area

LoadTranser

Load Transer through the pavement structure


19/369


20/369

Each o a pavements three primary componentsdescribed above, serves a specic, although

dierent purpose, as explained below.

1.2.1 Suracing

The suracing is the pavements interace withthe trac and the environment, its unction be-ing to protect the pavement structure rom both,providing durability and waterproong.Protection rom trac. Trac aects the suracingin two ways:

stresses imparted by wheel loads at the suraceare predominantly in the vertical plane, but

horizontal stresses can become signicant,particularly with the turning and braking actions o

trac and on steep gradients. The strength and

stiness characteristics o the material used in

the suracing must be able to withstand all these

stresses without crushing or deorming; and

abrasion o tyres on the surace, especiallywhilst cornering, tends to polish the surace.In time this polishing eect reduces the rictionproperties (skid resistance) and texture deptho the surace. Such suraces become slippery,especially when wet, and can be hazardous.

Protection rom the environment. The suracingis continually being subjected to various orms oattack rom the environment.

Thermal eects, oxidation and ultraviolet radiationare most aggressive. A suracing thereore needsto have the ollowing properties:

1.2 Pavement components

Upper layers Base course surace

Stratum (top o subgrade)

Surace layer

Wearing courseBinder courseBase course

Subbase course

Capping layer and / orselected subgrade

Embankmentor Fill

Lower layers (select subgrade and ll)

Subgrade

Road design in embankment and cut


21/36918 //19

1.2.2 Structural layers

elasticity to allow it to repeatedly expand andcontract as the temperature changes; and

durability to absorb the daily bombardment oultraviolet radiation, sporadic exposure to waterand chemical eects whilst maintaining accept-able perormance.

In addition to skid resistance, the bituminous sur-acing provides fexibility, durability and superiorwaterproong. Hot-mix asphalt (with a bitumencontent o approximately 5% by mass) is generallyused as a premium suracing or heavily trackedroads, whilst the more economical chip-seal

surace treatments are applied where the tracvolumes are lower.

The pavement structure transers the load rom thesurace to the subgrade. As previously described,the stresses applied by a wheel at the suraceare eectively reduced within the pavement struc-ture by spreading them over a wide area o thesubgrade.The pavement structure generally consists oseveral layers o material with dierent strengthand stiness characteristics, each layer servingthe purpose o distributing the load it receivesat the top over a wider area at the bottom.The layers in the upper part o the structureare subjected to higher stress levels than those

lower down and thereore need to be constructedrom stronger and stier material.The gure on the previous page shows the di-erent layers that are typically used to constructfexible pavements.

The response o a layer to an imposed load de-pends largely on the material properties (elasticity,plasticity and viscosity) and the characteristics othe load (magnitude, rate o loading, etc.).

Flexible pavements are constructed rom threetypes o material:

Unbound (granular) materials, which includecrushed stone and gravels, transer appliedloads through the individual particles, orskeleton, o their matrix. Inter-particle rictionmaintains structural integrity, but under repeatedloading (oten associated with an increasein moisture content), a gradual densicationprocess occurs as the particles re-orientate andmove closer together. This can occur at any levelin the pavement structure, ultimately resulting indeormation at the surace. Such deormation is

normally maniest as wide radius rutting in thewheel-paths.

Moisture

Air voids

Aggregate

Unbound Granular


22/369

Bound materials, which include cement stabi-lised materials and asphalt, act more like a widebeam. Applying a vertical load to the suraceo a beam generates horizontal compressivestresses in the upper hal o the beam andhorizontal tensile stress in the lower hal, with

maximum horizontal stresses at the top andbottom. The strain resulting rom these stresses,particularly the tensile strain at the bottom,ultimately leads to a atigue type o ailure atermany load repetitions. Cracks develop at thebottom o the layer and then propagate verticallyas the load repetitions continue.

Non-continuously bound materials, which com-prise bitumen stabilised materials (BSMs) with

either oamed bitumen or emulsied bitumen

as binders, behave like granular materials withretained inter-particle riction but increased cohe-

sion, and stiness. Permanent deormation is the

main mode o distress o BSMs. Bitumen is non-

continuously dispersed in these materials and

atigue is thereore not a design consideration.

Deormation occurring in unbound and non-con-tinuously bound material and atigue cracking obound material are both related to the number oload repetitions. This allows the unctional lie o a

pavement to be determined in terms o the numbero times it can be loaded beore it ails, termedthe structural capacity o the pavement.

Note:

Bitumen stabilised materials (BSMs) are

non-continuously bound

Bound Hot Mix Asphalt

Non-continuously bound Bitumen stabilised

Bitumencomplete coating

Moisture

Aggregate

AggregateBitumen spotwelds


23/36920 //21

The natural material supporting a pavementstructure can be either in-situ material (cut condi-tion) or imported (ll condition). The strengthcharacteristics o this material dictate the typeo pavement structure required to spread theapplied surace load to a magnitude that can be

supported without the subgrade ailing due topermanent deormation.

Pavement design methods usually use subgradestrength and stiness as primary input parametersand aim at providing a structure o sucient thick-ness and strength to protect the subgrade.

This approach was rst adopted in the 1950swith the empirical Caliornia Bearing Ratio (CBR)cover design method and has endured into the21st century. In general, thick pavement structuresare required to protect poor subgrades and suchthickening is oten achieved by the addition o

selected subgrade, or capping layers.

In some cases, subgrades can comprise collaps-ible soils, heaving clays, sot / consolidating claysand dispersive / erosive soils. For such conditions,specialist geotechnical investigations, testing anddesign is required.

1.2.3 Subgrade


24/369

Roads are built throughout the world in all typeso climate, rom hot dry deserts to high rainallregions and icy tundra conditions. Yet, regardlesso the environmental conditions, every road isdesigned to withstand trac loading by the sameundamental mechanism o transerring the high

intensity orces imparted at the surace by thewheel loads to lower levels that the subgrade canaccommodate without deorming.

The specic environmental conditions and antici-pated trac loading are the two primary structuraldesign considerations or any pavement andare discussed separately below. These actorsdetermine the pavement condition and rate odeterioration. Generally, pavement deterioration

is measured indirectly by assessing riding quality,but obvious visible eatures such as rut depth andsurace cracking are also relevant. Each mecha-nism o distress has its own dening perormanceunction versus time as shown in the gure below.

1.3 Primary considerations

or the pavement structure

Evolution o Pavement Distress

Terminal Condition

Riding Quality

Rutting

Cracking

Time

Pavementc

ondition


25/36922 //23

Environmental conditions are considered separate-ly or the suracing and the underlying structurallayers.

The suracing. In addition to trac, road suracesare exposed to sunshine, wind, rain, snow and

other natural elements. O importance are the con-sequences o these elements on the engineeringproperties o the road surace which maniest in:

thermal eects which cause changes in volumeas materials expand and contract in response tochanging temperatures. The daily temperaturerange o the road surace is important. In desertareas, the surace o a blacktopped road canexperience a temperature range in excess o

70 C between dawn and noon, whereas roadsuraces inside the Arctic Circle during winterwill be buried under snow and ice and thereoreremain at a relatively constant temperature;

reezing eects which create the phenomenonknown as rost heave. Repeated reeze / thawcycles can cause major damage to road sur-aces;

radiation eects which cause road suraces toexperience a type o sunburn. The ultraviolet

radiation to which the road surace is subjectedcauses the bitumen to oxidise and become brit-tle. This process is known as ageing; and

moisture eects where rainall penetrates thevoids o the suracing and builds up pore pres-sures under wheel loading, breaking the bondbetween the bitumen and the aggregate, leadingto stripping and ravelling o the asphalt.

The pavement structure. Water is the great-est enemy o road structures. Water saturationcauses materials to soten and deteriorate, andalso provides inter-particle lubrication when loadis applied. The bearing capacity o a material in adry state is signicantly greater than in a wet state

and the more cohesive (or clayey) the material,the more susceptible it is to moisture. In addition,water that is present when rost progresses into apavement structure will expand and cause exten-sive damage when it thaws. Hence the importanceo preventing water ingress into a pavement struc-ture, especially into the poorer quality materialsound in the lower layers.

1.3.1 Environmental conditions


26/369

Environmental actors are responsible or mostcracking that initiates at the surace. The majorcontributor to this phenomenon is ultraviolet radia-tion rom sunlight that causes a continuous slowhardening o the bitumen. With hardening comes areduction in elasticity that results in cracking when

the surace contracts as it cools or fexes underwheel loads.

Once the surace integrity has been lost due tocracking, the pavement tends to deteriorate at anaccelerated rate due to water ingress. The primaryenvironmental actors eecting pavements areshown in the gure below.

Environmental eects

Bitumen sotening/ageing

Radiation

Stripping / water ingress /loss o shear strength

Frost heave


27/36924 //25

Roads are constructed to carry trac. The volumeand type o trac that a road is expected to carrydictates the geometric and structural require-ments. Transportation engineers work with antici-pated trac statistics (in terms o vehicle numbers,composition and sizes) in order to determine

the geometric capacity requirements (alignment,number o lanes, etc.). Pavement engineers needanticipated trac statistics (in terms o vehiclenumbers, conguration and axle mass) to deter-mine the structural requirements. Accurate predic-tions o uture trac volume and type is thereoreo paramount importance.

Important eatures o the trac rom a pavementdesign perspective are those that allow denitiono the magnitude and requency o surace loads

that the road can anticipate during the expectedlie o the pavement. The load that is imparted ona road surace by a tyre is dened by three actors:

orce (in kN) actually carried by the tyre which,together with

infation pressure (in kPa) determines theootprint o the tyre on the road. This ootprintdenes the area on the surace that is subjected

to the load, andspeed o travel that denes the rate at which thepavement is loaded and unloaded.

Passenger cars typically have tyre pressures inthe range o 180 to 250 kPa and support less than350 kg per tyre, or 7 kN on an axle. This loadingis structurally insignicant when compared to thatimparted by a large truck used or hauling heavyloads, which range between 80 and 130 kN per

axle (depending on legal limits and mass control)with tyre pressures ranging between 500 to1,300 kPa. Clearly, the loading o such heavyvehicles will have the greatest infuence on thestrength requirements o a pavement and is there-ore discussed in Chapter 2, Pavement Rehabilita-tion and covered in detail in Appendix 2, Determin-ing Structural Capacity rom Trac Inormation.

1.3.2 Tra c loading

Trac loading

Axel load Tyre pressure

Contact area

Stressdistribution

Vehiclespeed


28/369

1.4 Pavement distress mechanisms

Trac loading is responsible or the developmento ruts and or cracking that initiates within thebound layers. Every vehicle using a road causesa small measure o deormation in the pavementstructure. The deormation caused by a light vehi-cle is so small that it is insignicant whilst heavily

loaded vehicles cause relatively large deorma-tions. The passage o many vehicles has a cu-mulative eect that gradually leads to permanentdeormation and / or atigue cracking. Overloadedaxles cause a disproportionate amount o dam-age to the pavement structure, accelerating suchdeterioration. This deterioration is caused by twodierent mechanisms, namely:

permanent deormation caused by densication,

where stresses rom repeated loading causethe individual particles within the pavementlayer to move closer together, resulting in aloss o voids or shearing o particles past eachother (localised shear ailure). In granular and

non-continuously bound material, such a losso voids leads to an increase in strength (densermaterials are stronger).In asphalt the converse applies. It must, how-ever, be appreciated that a reduction in the voidcontent in asphalt not only causes rutting in the

wheel paths, but it also allows the bitumen tostart acting as a fuid when warm, creating amedium or hydraulic pressures to be gener-ated rom the imposed wheel loads. This causeslateral displacement, or shoving along the edgeso ruts; and

atigue cracking o bound materials. These initi-ate at the bottom o the layer where the tensilestrain caused by wheel loads is at its maximum.These cracks then propagate to the surace. Top

down cracking can occur in thick asphalt layers.Permanent deormation o the underlying mate-rial exacerbates cracking by eectively increas-ing the tensile strain imposed by wheel loads.

Once a crack penetrates through the protectivesuracing, water can ingress into the underlyingpavement structure. As previously described,the sotening eect o water leads to a reductionin strength that results in an increased rate o dete-rioration under repeated wheel loads.

In addition, water in a saturated material becomesa destructive medium when the pavement comesunder load. Similar to a hydraulic fuid, the water

transmits predominantly vertical wheel loads intopressures that rapidly erode the structure o agranular material and causes stripping o bitumenrom the aggregate in asphalt. Under these condi-tions the nes ractions o the pavement materialare expelled upwards through the cracks (knownas pumping) resulting in voids developing withinthe pavement. Potholing and rapid pavement dete-rioration soon ollows.

1.4.1 Advanced pavement distress


29/36926 //27

Where temperatures drop below 4 C, any reewater in the pavement expands as it reezes,creating hydraulic pressures, even in the absenceo imposed wheel loads. Frost heave causedby repeated reeze / thaw cycles are the worstscenario or a cracked pavement, resulting in rapiddeterioration.

Under dry desert conditions, cracks in the surac-ing lead to a dierent type o problem. At nightwhen temperatures are usually relatively low (otenbelow reezing) the surace contracts, causing thecracks to widen and act as a haven or wind-blownsand. When temperatures rise during the day, thesurace is restricted rom expanding by the sandtrapped within the crack, resulting in large horizon-tal orces that cause localised ailure (spalling) atthe edge o the crack.

These orces can ultimately lead to the suracingliting o the pavement structure in the vicinity

o cracks, making or extremely poor ridingquality.

Another ailure condition oten seen in desertenvironments is block cracking caused by anextremely low moisture content in dense material.

This phenomenon is known as pore fuid suctionpressure. Due to the low relative humidity regime,water is lost rom the pavement structure due toevaporation, reducing the moisture content tolevels similar to those achieved when air dryingsamples in the laboratory. At such low moisturecontents, the menisci o the tiny water dropletsremaining within the small voids o a compactedmaterial exert sucient tensile orces to cause thematerial to crack.

This condition is likely to maniest whereverrelative humidity levels are low and the road isunsealed, allowing the moisture in the pavementstructure to evaporate. It has also been cited asthe cause o top-down cracking at high altitudes(> 2,000 m). The only eective treatment or thiscondition is to seal the road so that the equilibriummoisture content is retained (i.e. the hydro-genesiseect). I the material is allowed to dry out, severeand deep cracking will occur, even in compacted

sand. I the material is allowed to wet up, capillaryorces will reduce and the apparent cohesion willdissipate.

One urther cause o surace cracking, particularlyin thin asphalt suracings, results rom the lack otrac. The kneading action o trac keeps bitu-men alive. Oxidation and subsequent hardeningcauses thermal cracks to initiate at the suraceo the bitumen binder. Subjecting the bitumen tostress repetitions causes sucient strain to close

the cracks as they orm, thereby preventing themrom propagating.

Typical pavement distress with pumping


30/369

Pavement maintenance activities are normallyocused on keeping water out o and away romthe pavement structure. This involves maintainingthe suracing in a waterproo state and ensuringthat drainage measures are eective so that watercannot pond on the road surace or along the road

edge.

Water normally ingresses the upper pavementstructure through cracks in the suracing, otenassisted by water ponding on the surace. Cracksshould thereore be sealed as they appear androad verges trimmed to promote runo. I ad-dressed early, ageing eects can be eectivelytreated by the application o a light og spray odilute bitumen emulsion. More serious condi-tions require a chip seal application where trac

volumes are low, or a conventional hot-mix asphaltoverlay.

Such measures, which are aimed at maintainingthe fexibility and durability o the suracing, onlyreally address deterioration due to the environ-

ment. Deormation and atigue cracking causedby trac loading cannot be treated eectivelyby supercial maintenance activities and requiresome orm o structural rehabilitation.

Pavement deterioration begins at a relatively slow

pace. Pavement indicators can be used to monitorthe rate o deterioration. Road authorities otenemploy a data-base system, known as a Pave-ment Management System (PMS), to continuouslymonitor the riding quality o all road pavementswithin their network, thereby drawing attention tothose that most require attention. The gure belowprovides a typical PMS plot that illustrates theeectiveness o timely maintenance and rehabilita-tion measures.

This gure highlights the importance o takingtimeous action to maintain as high a riding qualityas possible. The rate o deterioration is indicatedby the riding quality. Poorer riding quality encour-ages aster rates o deterioration through dynamicloading. As the riding quality reduces, the scale o

1.5 Pavement maintenance and

structural rehabilitation

Managing pavement maintenance and rehabilitation by monitoring riding quality

Consequences onot resuracing

Resuracing

Terminal riding quality

Structural rehabilitation

Structural DesignPeriod

Constructedriding quality

Time / Traic

Ridingquality


31/36928 //29

remedial measures becomes greater, as does thecost o such measures.

The decision as to which remedial measures toundertake to either improve a pavement or justmaintain it at its current riding quality is oten

dictated by budgetary constraints. Short-termholding measures can be extremely cost eective.Pavement rehabilitation is sometimes postponed

until it is combined with an upgrading exercise toimprove the geometrics o the road and add ad-ditional lanes. Each rehabilitation decision needsto be taken independently within the context o theoverall road network. But, to do nothing and allowthe pavement to deteriorate urther is generally the

worst decision because o the exponential rate odeterioration with time.


32/369

1.6 Rehabilitation options

There are usually many options available or the re-habilitation o a distressed road and sometimes itis dicult to determine which is the best. However,the answer to two important questions that mustbe asked at the outset will assist in selecting thecorrect one, the one that is most cost-eective

in meeting the road owners needs. The two impor-tant questions are:

what is actually wrong with the existing pave-ment? A cursory survey consisting o a visualinspection coupled with a ew basic tests (eg.defection measurements) will normally besucient to be able to understand the distressmechanism. O importance is to determinewhether the distress is conned to the suracing

(upper pavement layers) or whether there is astructural problem; and secondly

what does the road authority really want andwhat can they aord? Is a 15-year design lieexpected, or is a smaller capital outlay envis-aged that will arrest the current rate o deteriora-tion and hold the pavement together or a urtherve years?

The answers to these two questions will narrowdown the rehabilitation options to only those thatwill be cost-eective within the context o, essen-tially, the nature o the problem and the time rame.By separating the nature o the problem into twocategories (surace and structural) rom the time

rame (short-term or long-term), selecting the bestoption is simplied.

One other important point that aects the decisionis the practicality o various rehabilitation methods.Trac accommodation, weather conditions andavailability o resources can all have a signicantinfuence on how a project is executed and maypreclude certain options.

This whole exercise has one sole purpose:

determining the most cost-eective solution to theactual problem within the context o the projectenvironment.

Note:

Rehabilitation design must address the root

cause o distress cost eectively


33/36930 //31

Surace rehabilitation measures address prob-lems that are conned to the uppermost part othe pavement, usually within the top 50 mm to100 mm. These problems are normally related toaging o bitumen and cracking that initiates at thesurace due to thermal orces.

The most commonly used methods or dealingwith this type o problem include:

Asphalt overlay. Paving a thin (40 50 mm)hot-mix asphalt overlay on the existing sur-ace. This is the simplest solution to a suraceproblem since the time required to completethe work is short and there is minimal impact on

the road user. Modied binders are oten usedin the asphalt to improve perormance, therebyextending the lie o the overlay. Active cracks inthe existing surace will refect quickly through anew overlay and thereore need to be identiedand addressed either by applying a stress-reliev-

ing bandage or by patching. Repeated overlays,however, increase road surace elevations thatcan cause drainage and access problems.

1.6.1 Surace rehabilitation

Asphalt overlay

Existing pavement


34/369

Mill and replace. This method removes theoending cracked layer o asphalt and replacesit with resh hot-mix asphalt, oten with a modi-ed binder. The process is relatively ast due

to the high production capabilities o modernmilling machines. The problem is removed withthe layer o asphalt and pavement levels aremaintained.

Mill & Replace

Mill o all sphalt Replace asphalt


35/36932 //33

Recycling a relatively thin (100 mm 150 mm)layer o asphalt material rom the existing pave-ment. Such recycling can be done either in-

plant by transporting milled material to a coldmixing plant KMA 220 or in place by using the2200 CR or WR 4200.

Recycle upper 100 mm

Existing pavement

2200 CR

Mill o 150 mm asphalt

Place RAP in stockpile

Existingpavement

Pave110 mmthick layer

Pave 40 mmHMA suracing

Treat stockpiled RAP in KMA with2% oamed bitumen + 1% cement

Recycle upper 150 mm


36/369

Rehabilitation to address problems within thestructure o a pavement is normally treated as along-term solution. When addressing structuralproblems, it should be remembered that it is thestructure o the pavement that is distressed, sel-dom the materials within the structure. In addition,

upgrading an existing pavement by strengtheningthe structure (e.g. upgrading an existing gravelroad to blacktop standards) may be regarded as aorm o rehabilitation.

Densication (or compaction) o granular ma-terials is, in act, a orm o improvement sincethe higher density o a natural material leads tobetter strength characteristics. However, theconsequences o densication and the resulting

deormation can lead to problems maniesting inthe overlying layers, especially where such layersare constructed rom bound material.

As a rule, structural rehabilitation should aim tomaximise the salvage value o the existing pave-

ment. This implies that material that has densiedshould not be disturbed. The continuous kneadingaction o trac takes many years to achieve thisstate and the benets that such high densitiesoer should be utilised where possible.

Various options that are popular or structuralrehabilitation include:

1.6.2 Structural rehabilitation


37/36934 //35

Total reconstruction. This is oten the preerredoption when rehabilitation is combined with anupgrading exercise that demands signicantchanges to the alignment o the road. Essen-tially, reconstruction implies throw-away-and-start-again. Where trac volumes are high, it

is oten preerable to construct a new acility ona separate alignment, thereby avoiding tracaccommodation problems.

Construction o additional layers (either romuntreated or treated granular material and / orasphalt) on top o the existing surace. Thickasphalt overlays are oten the easiest solution toa structural problem where the trac volumesare high. However, as described above, an

increase in surace elevations oten gives rise tounoreseen drainage and access problems.

Total reconstruction

Remove existing

distressed layers

Reconstruct each layer

(Conventional construction equipment)


38/369

Deep recycling to the depth in the pavementat which the problem occurs, thereby creat-ing a new thick homogeneous layer that canbe strengthened by the addition o stabilisingagents. Additional layers may be added on topo the recycled layer where the pavement is to

be signicantly upgraded. Stabilising agents areusually added to the recycled material, especial-ly where the material in the existing pavement is

marginal and requires strengthening. Recyclingaims or maximum recovery rom the existingpavement. In addition to salvaging the mate-rial in the upper layers, the pavement structurebelow the level o recycling remains undisturbed.

Existingpavement

Recycle 250 mm deepAdd 2.5% oamed bitumen+ 1% cement

Pave 40 mm thick HMA suracing

Deep recycling


39/36936 //37

Combining two recycling methods, in-placewith in-plant. This option allows or an increaseddepth o existing pavement to be treated andrequires that a portion o the upper pavementbe initially removed and placed in temporarystockpile. The underlying material is then recy-

cled / stabilised in-place. The material placedin temporary stockpile is then treated in-plantand paved on top o the in-place recycled layer,

thereby achieving additional structural capac-ity. The thickness o the paved layer can beselected to suit the nal surace level require-ments. For example, where existing surace lev-els are to be maintained ater rehabilitation anda 40 mm thick asphalt suracing is required, the

thickness o paving or the upper stabilised layeris reduced by 40 mm to allow the nal suracelevels to match those prior to rehabilitation.

The purpose o considering several pavement re-habilitation options is to determine the most cost-eective solution. This manual is aimed at provid-ing sucient inormation together with a design

approach that will allow recycling to be includedas one o the options. Economic evaluations o thedierent options will then help identiy the optimalsolution, as discussed in the next chapter.

Mill o 150 mm asphalt

Place RAP in stockpile

Existingpavement

Recycle 200 mmdeep and stabilisewith cement oroamed bitumen

Pave 150 mmthick layer

Pave 40 mmHMA suracing

Treat stockpiled RAP in KMA with2% oamed bitumen + 1% cement

Two -part recycling


40/369

2.1 General 41

2.2 Pavement rehabilitation: investigation and design procedure 42

2.3 STEP 1: Data acquisition / process available inormation 44

2.3.1 Inormation on the existing pavement (historical inormation) 45

2.3.2 Design traic 46

2.4 STEP 2: Preliminary investigations 48

2.4.1 Determination o uniorm sections 49

2.4.2 Visual inspection 52

2.4.3 Reassessment o uniorm sections 54

2.5 STEP 3: Detailed investigations 55

2.5.1 Excavating Test Pits 55

2.5.2 Laboratory testing 56

2.5.3 Extracting core specimens 57

2.5.4 Dynamic cone penetrometer (DCP) probes 58

2.5.5 Analysis o delection measurements 60

2.5.6 Rut depth measurements 60

2.5.7 Synthesis o all available data 61

2.6 STEP 4: Preliminary pavement rehabilitation design options 62

2.6.1 Pavement design approach 62

2.6.2 Catalogue design methods 63

2.6.3 Structural number method 63

2 Pavement rehabilitation


41/36938 //39

2.6.4 Pavement number method 64

2.6.5 Mechanistic design methods 66

2.6.6 Delection based methods 67

2.6.7 Summary o pavement design approaches 67

2.7 STEP 5: Laboratory mix design 68

2.8 STEP 6: Finalise pavement design options 70

2.9 STEP 7: Economic analyses 71


42/369

As was explained in the previous chapter, pave-ments deteriorate with time and usage. As theend o the service lie approaches, the rate odeterioration in the riding quality increases dueto deormation, cracking, potholing and othersuch distress symptoms. The maintenance e-

orts necessary to hold the surace together andmaintain an adequate level o service tend toescalate until the point is reached where it makes

more economic sense to rehabilitate the wholepavement rather than addressed localised areas odistress. Although there are no denitive guidelinesand each road has its own unique eatures, thereappears to be general consensus that once 15%o the surace area has been patched, it is cheaper

to rehabilitate the whole road than to continue ap-plying patches on an ad hoc basis.

Heavy patching indicates the end o the service lie


43/36940 //41

2.1 General

Pavement rehabilitation is the term used to de-scribe the work required to reinstate a distressedroad and restore the structural integrity o thepavement. Where a road is properly designed andconstructed and where routine maintenance andresuracing interventions are undertaken timeously,

the need or rehabilitation can be delayed untilthe pavement reaches a terminal condition due tostructural deterioration. However, in practice, suchmaintenance and resuracing activities are otennot carried out, resulting in the need or the pave-ment to be rehabilitated sooner than was originallyenvisaged. In addition, pavement rehabilitationis oten included with strengthening and / or geo-metric improvements required to accommodateincreased trac volumes.

This chapter describes the various steps that areincluded in a pavement rehabilitation exercise.These are explained and guidelines given in orderto provide a practical overview o an extremelyinvolved (and at times complex) process that hasrecently become an area o specialisation in theeld o Pavement Engineering. These explanationsand guidelines are certainly not all-inclusive andreerence should be made to the literature includedin the Bibliography (ater Chapter 6) should more

detailed inormation be required.

The various steps in a pavement rehabilitationexercise include gathering o relevant inorma-tion (e.g. trac data), conducting surveys andtests to identiy and determine the compositionand condition o the various layers in the existingpavement structure (e.g. defection measure-

ments), summarising and interpreting all availabledata to allow alternative design options that meetthe required design lie (structural capacity) to beormulated and, nally, to decide which option ismost attractive. Although these steps are commonto all pavement rehabilitation exercises, the ocuso this chapter is on identiying and understandingthe materials in the upper pavement structure andtheir potential or being recycled.

A fowchart is included to illustrate the various

steps and methods used in the pavement rehabili-tation exercise. Methods that are normally used orinvestigating distressed pavements are outlined.Dierent methods or designing pavements aredescribed, particularly those most suited to pave-ments that are rehabilitated by recycling.


44/369

The need or rehabilitation is usually triggered byan unacceptable level o distress that refects asa poor surace condition (e.g. bad riding qual-ity, pothole development, etc.), oten highlightedand prioritised by using an appropriate PavementManagement System (PMS). Once a road has

been identied or rehabilitation, a ull pavementinvestigation and design procedure needs to beollowed to determine the most appropriate reha-bilitation solution.

The primary objectives or investigating an existingpavement are to determine the composition o thepavement structure, gain an understanding o thebehaviour o the materials in the various layers andestablish the cause o distress that has increasedthe demand or maintenance measures.

The fowchart on the acing page is applicableto all rehabilitation projects and can be adaptedaccording to specic needs. The various activitiesare grouped under seven sequential steps:

Step 1. Acquisition o available inormation

Step 2. Preliminary investigations and identica-tion o uniorm sectionsStep 3. Detailed investigation o each uniorm

section and synthesis o all dataStep 4. Preliminary pavement design options

based on estimates o stabilised materialproperties

Step 5. Laboratory mix designs to determinestabilised material properties

Step 6. Pavement design nalisationStep 7. Economic and other analyses to indicate

the optimal solution

The ollowing sections describe each step in detail.

2.2 Pavement rehabilitation:

investigation and design procedure


45/36942 //43

Dene the Roads Authoritysspecic requirements

Data Acquisition

NO

STEP 1

STEP 2

STEP 3

STEP 4

STEP 5

STEP 6

STEP 7

NO

YES

YES

Sucient data?e.g. trac

Preliminary investigations /identiy uniorm sections

Detailed investigationsSynthesis o all inormation

Formulate preliminary pavementdesign options based on estimates

or stabilised material properties

Laboratory mix designs

Finalise pavement design options

Conduct economic analyses

Were the properties estimated orstabilised material achieved?

Acquire additional inormation

Consider alternative options available orchanging the material properties:

- dierent stabilising agent- import resh material (dilution)

- recycle deeper, etc.

Process data


46/369

At the start o every pavement rehabilitation exer-cise, those responsible or ormulating the designmust have an unambiguous understanding o whatis required in terms o:

Design lie. Is a short-term or long-term servicelie required?

Functional properties o the rehabilitated road(e.g. specic requirements or riding quality, skidresistance and noise levels)

Available budget. The level o unding availableor the rehabilitation works and or the routinemaintenance measures that will be required dur-ing the service lie.

These requirements provide the design engineerwith the scope and limits o the project. The inves-tigation phase commences by sourcing all inor-mation on the existing pavement that is available.This inormation alls under two major headingsdescribed below:

records o historical inormation; and

trac data to determine the structural capacityrequirements.

2.3 STEP 1: Data acquisition / process

available inormation


47/36944 //45

All available inormation should be sourced andanalysed in order to place the project in contextand provide an early appreciation o what can beexpected when starting the eld investigations.Where available, construction and maintenancerecords can provide valuable inormation on:

details o the pavement that was originallyconstructed;

the thickness o as-built layers;

details o materials used in the constructiono the original layers as well as those used inany subsequent rehabilitation or improvementmeasures;

results o quality control tests conducted duringconstruction; andgeological data along the route.

In addition, as much inormation as possibleshould be obtained about locally available con-struction materials. The type, quality and quantityo materials that can be obtained rom both com-mercial sources and previously opened borrowpitsand quarries should be investigated or possible

use in the rehabilitation works. Also, the locationand distance rom site o any established asphaltplant should be established.

Furthermore, meteorological records rom theclosest weather station should be obtained andanalysed to determine seasons that are best suitedor the type o construction that is envisaged.

The proximity o locally available materials will infuence rehabilitation options

2.3.1 Inormation on the existing pavement (historical inormation)


48/369


49/36946 //47

Pavements are thereore designed to provide or aspecic structural capacity. Although a design lieis oten quoted in years, pavements are actuallydesigned to accommodate the number o loadrepetitions that are anticipated during that period.

Any unoreseen changes in the estimated trac

loading will thereore impact on the design lie.This is one o the most undamental aspects opavement engineering and is so important that aull explanation is included in Appendix 2, entitledDetermining Structural Capacity rom TracInormation.

Obtaining additional trac inormation

Where the available trac data is insucient,particularly when designing the rehabilitation oheavy pavements, additional inormation must

be obtained. Classied trac counts should beundertaken and weigh-in-motion data obtained toestimate the percentage o heavy vehicles

currently using the road, the average number oaxles per heavy vehicle and the average masscarried on each axle. This inormation should besupplemented wherever possible with inormationobtained rom weighbridge stations (including theresults o any tyre pressure surveys).

It must always be borne in mind that the inorma-tion used to calculate structural capacity is basedon assumptions concerning trac growth rates,damage actors and other data that can only beestimated. It is thereore important to carry outsensitivity analyses to understand the conse-quence o varying these estimated parameters.

Weigh-in-motion station to measure and record axle loads

Weight sensor

Data capture


50/369

Beore any eld surveys or investigations com-mence, it essential that the existing road suraceis accurately pre-marked with an appropriatereerencing system (usually the chainage or kmdistance (e.g. km 121 + 400) is adopted). It is nor-mal to paint prominent marks every 20 m on the

centre-line or outer edge o the carriageway andto write the chainage value every 100 m. Thesemarks are then used as the primary reerence orall survey and test locations.

Road pavements are seldom uniorm over longdistances. Both the underlying geology and thematerials used in the construction o the individuallayers will vary along the length o the road. Allroads are thereore comprised o a series o dier-ent sections o relative uniormity and the length o

each section will be dierent. These sections areknown as uniorm sections and may be as shortas a ew hundred metres or as long as several kilo-metres. Uniorm sections are identied visually bychanges in distress patterns. Defection measure-ments are also useul or identiying dierences inthe underlying pavement structure.

2.4 STEP 2: Preliminary investigations


51/369

One o the main objectives o undertaking prelimi-

nary investigations is to identiy uniorm sections.

This is usually achieved by analysing available con-

struction records, analysing any defection data, and

rom conducting a comprehensive visual inspection.

Similar distress symptoms and / or defection meas-

urements indicate similar conditions in the underly-ing pavement structure. This inormation is used

to identiy the boundaries between the dierent

uniorm sections, and the type o distress (indicating

the mode o ailure). The ollowing sections describe

how this is achieved in practice.

Defection method

When a load is applied to the surace o a road,the pavement defects. Defections may be meas-ured by applying a load on the pavement, either an

impulse (alling weight) or a known wheel load thatsimulates a heavy vehicle. The magnitude o thedefection that occurs under a given load, as wellas the shape o the defection bowl produced bythe load, provides a useul means o assessing thein-situ properties o the pavement.

Various methods or measuring pavement defec-tion have been developed, primarily or use asindicators o the structural condition and load car-rying capacity o the pavement. Those most widelyused are the Benkelman Beam and the FallingWeight Defectometer (FWD).

48 //49

Measuring pavement defections using a FWD

2.4.1 Determination o uniorm sections


52/369

As primary input or their PMS, road authoritiesnormally carry out defection surveys at 3 to 5 yearintervals on all major roads in their network. Whereavailable, such inormation is invaluable or theinitial denition o uniorm sections using simplestatistical techniques (cumulative-sum analysis)to identiy where changes occur. The cumulative-sum values o maximum defections are calculated

using the ormula:

where Si = cumulative-sum value at location i; i = maximum defection at location i;

and mean = mean o maximum defection or

the entire section.Si-1 = cumulative-sum value at location

beore location i

The cumulative-sum value is then plotted at each

respective location, normally together with the

maximum defection value plotted on the same

graph, as shown in the sketch opposite. A relatively

constant slope or the cumulative-sum plot indi-

cates sections o similar pavement response, or a

uniorm section.

Note: The cumulative-sum method is not re-stricted to maximum defection. This method isoten used with other defection indices, such asthe Surace Curvature Index (SCI).

Other methods

Where no defection data is available, uniorm sec-tions must be identied by other means. As-builtconstruction inormation (when available) is otenused as an initial guideline, supplemented by adetailed visual assessment, as discussed below.However, when the required structural capacity othe pavement exceeds 10 million ESALs, it is al-ways advisable to undertake a FWD survey at the

The sketch below illustrates typical defection bowls measured on two dierent pavements.

(equation 2.1)Si = (i mean) + Si-1

Typical defection bowls

Maximum defection

Soter material Stier material

wheel / impulse load


53/36950 //51

outset. In addition to identiying uniorm sections,the inormation derived rom such a survey isinvaluable or the statistical assessment o variousin-situ pavement properties (see Section 2.5.5).

Identication o uniorm sections

30,000 30,100 30,200 30,300 30,400 30,500 30,600 30,700 30,800

= Maximum defection (d)

= Cumulative sum (S)

Distance (m)

Uniorm sections

Cumulativesum

Maximumdefection(10-2mm)

300

200

100

0

-100

-200

-300

-400

250

200

150

100

50

0

Note:

Cumulative-sum methods can be used to

identiy uniorm sections based on defectionmeasurements or other relevant inormation(e.g. subgrade CBR value) collected alongthe length o the road.

Distance (m)Maximum

defection (d)

Cumulative

sum (S)

30,060 64.80 -41.14

30,080 76.70 -70.38

30,100 86.60 -89.71

30,120 94.00 -101.65

30,140 79.10 -128.49

30,160 72.70 -161.73

30,180 71.30 -196.36

30,200 79.50 -222.80

30,220 82.40 -246.34

30,240 71.70 -280.58

30,260 76.80 -309.71

30,280 78.90 -336.75

30,300 110.40 -332.29

30,320 98.70 -339.53

30,340 86.70 -358.76

30,360 97.40 -367.30

30,380 139.60 -333.64

30,400 134.70 -304.88

30,420 164.00 -246.81

30,440 129.50 -223.25

30,460 142.50 -186.69

30,480 152.30 -140.33

30,500 150.10 -96.16

30,520 163.50 -38.60

30,540 198.90 54.36

30,560 119.60 68.02

30,580 208.60 170.69

30,600 132.80 197.55

30,620 72.10 163.71

30,640 63.20 120.98

30,660 61.10 76.14

30,680 29.80 0.00

Mean (D) 105.94

1 2 3


54/369

Visual inspections are undertaken by walking thelength o the road and recording all relevant ea-tures that can be observed or detected. Detailednotes are taken o all distress that is evident at thesurace over the ull width o pavement as well asother observations concerning drainage, geologi-

cal changes and geometric eatures, (e.g. steepgrades, sharp curves, cuttings and high embank-ments). The mode and type o distress that can

be recognized during the inspection are normallyclassied into the categories shown below.

2.4.2 Visual inspection

Mode o distress Type o distress Description

Surace damageEnvironmental damage

Trac damage

Ravelling, stone lossThermal crackingRutting (asphalt)

Stripping, bleeding, polishing

Structural damagePermanent deormation

CrackingAdvanced damage

Rutting in wheel pathsLateral shoving

Longitudinal in wheel pathsCrocodile

Other (transverse, etc.)Potholes, patches, etc.

Functional conditionDrainage

Riding quality

Erosion, washouts, etc.Edge break

Undulations, corrugations, etc.

The dierent modes and types o pavement dis-tress are recorded or each occurrence in terms olocation, severity and requency. Visual inspectionsprovide valuable clues regarding the causes opavement distress since ailure patterns tend tobe highlighted when all the data is summarised onone sheet. This eature is illustrated in the exampleshown opposite.

Whilst carrying out the visual inspection, digitalphotographs o the road surace are normallytaken at regular intervals ( 250 m in both direc-tions) and to record specic eatures (e.g. localisedailure). In addition, video clips are powerul toolsor recording trac-related problem areas thatshould be addressed under the rehabilitation pro-

ject (e.g. dangerous trac movements).

Note:

Visual inspection data provide valuable clues

regarding the cause o distress


55/36952 //53

Visual inspection

National Road 1 Section 12

Good City to Hellngone

km 30 - 36

Riding qualityCondition

rating

Sound

Warning

Severe

Comments

Defection

Instrument

measurement

Visua

l

assessm

ent

Rutting

Cracking

Disintegration (Surace)

Poor shape(no camber)

Dangerousintersection

Erosiondownstream

Deormation

Smoothing (bleeding)

Patching

km 30 31 32 33 34 35

culvert culvert culvert culvert culvert culvert

Cross access River

To Hellngone To Good City


56/369

Distress conned to the suracing Distress due to structural inadequacy

2.4.3 Reassessment o uniorm sections

The uniorm sections initially determined romdefection analyses should then be reassessed us-ing inormation rom the visual inspection, togetherwith all other available inormation (e.g. construc-tion records). This process allows a more accurate

denition o the boundaries between individualuniorm sections and acilitates the identication osections with a similar pavement structure.

The primary dierence between surace and struc-tural distress is shown graphically in the ollowingscetches.


57/36954 //55

For each uniorm section, a detailed investiga-tion is required to evaluate the existing pavementstructure (components and mode o distress)

and to determine in-situ subgrade support. Thetests and surveys normally employed in a detailedinvestigation are described below.

Test pits are without doubt the most importantsource o inormation concerning an existingpavement structure. In addition to gaining a visualappreciation o the dierent layers and materials inthe pavement structure, test pits provide the op-portunity to determine the in situ condition o thevarious materials and to take bulk samples romeach layer or laboratory tests (or classiying the

materials and or stabilisation mix designs).

The ollowing important inormation can beaccurately determined rom test pits:

individual pavement layer thickness;moisture content o the in situ material ineach layer;in situ density o the material in each layer; andcondition o the material in the various layers

(e.g. the degree o cracking, cementation orcarbonation o any cement-stabilised layer).

2.5.1 Excavating test pits

2.5 STEP 3: Detailed investigations

Example o testpit excavation and prole (Depth rom surace)

Asphalt

Cement stabilisedcrushed stone material

Crushed stone layer

Crushed stone layer

Dark Red Brown moist sandy silt + intactweathered granite aggregate

Cement stabilised crushed stone material

0 mm

85 mm

420 mm

555 mm

755 mm

900 mm

1.200 mm

Test pit


58/369

A minimum o two test pits are normally excavatedor each uniorm section, one where distress is evi-dent, and the other where there is no distress. Testpits are generally located in the outer wheel patho the trac lane and are sometimes positionedto straddle the shoulder and trac lane. Test pits

are usually 1.0 m in length (across the wheel path),0.75 m wide (along the wheel path) and at least1.0 m deep. Additional shallow slots (0.5 m wide)are oten excavated across the ull width o a tra-c lane as a means o investigating the depth towhich deormation extends and to determine theexistance o any pavement widening, as well asthe location o the boundary between the originaland widened pavements.

Test pits must be careully excavated so thateach individual layer o dierent material type canbe separated and removed independently. Eachtype o material encountered is careully removed(usually by hand) and heaped separately next tothe excavation or later sampling. As the digging

progresses, density and other in situ tests canbe carried out on each successive layer as it isexposed.Once the excavation is complete, the pavementprole is careully measured and recorded, asshown on the previous page. Bulk samples romeach dierent layer are retained or laboratory test-ing beore the test pit is backlled.

Bulk samples rom test pits are tested in thelaboratory to determine the quality o the mate-rial in each o the dierent layers, as well as theunderlying subgrade. The testing programme mustalso include samples o aggregates that may berequired or blending with any in situ recycledmaterial. Representative samples o such blendmaterials are to be obtained rom the same borrowpits and quarries that will be used as the respec-

tive sources or construction.

Laboratory tests normally carried out on thesesamples include: sieve analysis, Atterberg limitsand Caliornia Bearing Ratio (CBR). The resultsare primarily used or material classication, i.e. toprovide an indication o relevant parameters (suchas elastic modulus) or use in analysing the exist-ing pavement structure. The results are also usedto indicate the materials suitability or stabilisationand which stabilising agent(s) would be appropri-

ate.

2.5.2 Laboratory testing

Note:

Representative samples must be used for

laboratory tests


59/36956 //57

Note:

The recoverable length of a core specimen is

limited by the height o the core barrel used.

When determining the thickness of bound

layers rom recovered cores, ensure that ullrecovery is achieved (i.e. that the specimendid not break during extraction and / or thatdrilling continued to the bottom o the boundlayer).

Larger diameter core barrels (150 mm

diameter) are preerred, especially where thebound material includes aggregate largerthan 19 mm.

Unbound materials cannot be recovered and

sampled by coring.

Extracting core specimens by rotary drillingthrough layers o bound material is relativelyquick and less destructive than excavating testpits or inspection holes. Provided ull recoveryis achieved, core specimens can then be meas-ured to accurately determine the thickness o the

layer(s) o bound material (e.g. asphalt and cementstabilised material). Where required, core speci-mens recovered rom asphalt layers may be testedor volumetric composition / engineering proper-ties and the unconned compressive strengthdetermined by testing specimens recovered romcemented layers.

Extracting core specimens rom layers o bound material

2.5.3 Extracting core specimens


60/369

The DCP is a simple tool consisting o a steel rodwith a hardened steel conical tip that is driveninto the road pavement using a drop hammer ostandard mass alling a constant distance. Thepenetration rate, measured in mm / blow, providesan indication o the in situ bearing strength o the

material in the dierent pavement layers and achange in penetration rate indicates the boundarybetween layers. DCP probes are normally drivento a depth o 800 mm, or deeper into heavierpavement structures. The penetration rates canthen be plotted and used to indicate the thicknesso the various layers and the properties o the insitu material in each layer.

DCP penetration rates correlate well with the Cali-ornia Bearing Ratio (CBR) in relatively ne materi-

als and only reasonably well with coarser granularmaterials (at the in situ density and moisturecontent). Correlations o penetration rate with theUnconned Compressive Strength (UCS) o lightlycemented materials have also been developed.In addition, the DCP penetration rate provides arough but useul guide or the elastic modulus oin situ pavement materials.

Since the coecient o variation is oten rela-

tively high, numerous DCP probes are normallyrequired to achieve statistical reliability. Measure-ments should thereore be analysed statistically toobtain the relevant percentile value (normally the20th percentile is used or minor roads and the 5thpercentile or major highways).

Individual DCP penetration measurements arenormally taken once or every ve blows. Thesemeasurements are then analysed using computersotware to indicate in-situ CBR, UCS, Resilient

Modulus and layer thickness, as shown in theexample analysis opposite.

Diculties are sometimes experienced whenattempting to drive a DCP probe through coarseor bound material. A reusal condition is usuallydened by a penetration o < 1 mm or each otwo successive sets o 5 hammer drops (i.e. 100 NP

Gravel 65 SP

Sand 25 NP

S / grde 15 10

PI

90 93

90 Asphalt

190 GCS base

310 Gravels / base

150 Sand s / g

92

280

690

840

mm 0.80.60.40.2

0200400600800

0.640.57 0.49

DCPIndicatedstiness(MPa)

Cores

HMAthickness

mm

mm

mm

20406080

100100200300400500600700800

900


64/369

2.6.1 Pavement design approach

2.6 STEP 4: Preliminary pavement rehabilitation

design options

Once the investigations are complete and thesummary sheets described above have been com-piled, each uniorm section can be considered inisolation and relevant rehabilitation design optionsormulated. As with all diagnostic procedures, thekey to nding the best solution is to identiy all

possibilities at the outset. However, a sense o rea-sonableness must prevail in identiying alternativessince some will obviously be inappropriate (usuallydue to excessive cost and / or constructabilityimplications) and can be disregarded.

When all alternatives have been identied, a sub-jective selection process is then ollowed to iden-

tiy the three most appropriate options, therebyreducing the amount o analytical work requiredor designing the dierent pavements. These threealternative solutions must have similar structuralcapacities and, where a solution calls or additionallayers and / or a thick asphalt overlay, the implica-

tions o raising road levels must be included in theanalyses.

Pavement design or rehabilitation is dierent romdesigning new pavements, as discussed in theollowing sections.

Over the past 60 years, many pavement designmethods have been developed, ranging romrelatively simple empirical methods to the morecomplex modelling approaches that require so-phisticated computer sotware.

The various pavement design methods can besummarised under two primary headings:

Empirical methods. These include: the CBR cover design method, based on thestrength o the underlying subgrade; catalogue design approach, based on typical

pavement structures or specic applications; the DCP design method that uses data rom

DCP surveys to indicate shortcomings in exist-ing pavements;

the Structural Number method that assignscoecients to various material types; and

the Pavement Number method that usesintelligent structural numbers.

Analytical methods. These methods all includean analytical process that is ollowed by inter-pretation (empirical element) to translate theresults o the analyses to structural capacity(known as transer unctions): mechanistic analyses. These methods are

based on stress and strain analysis usingmulti-layer linear-elastic, elasto-plastic or nite

element models; and methods using defection measurements(defection bowl analyses).

As a general rule, more heavily tracked pave-ments (> 10 million EASLs) should always bedesigned using an analytical approach. An empiri-cal method may suce or lighter pavements but,where there is any doubt that a design may notbe appropriate or the anticipated trac loads, itshould be checked using an analytical method.


65/36962 //63

Catalogue design methods are prescriptive in thetypes and quality o materials required or a suit-able pavement structure. The catalogue providesa list o pavement types appropriate or dierentsupport conditions and structural capacities. Al-though this design approach is usually developed

using analytical procedures, it is both restrictive

(as it cannot include all options) and not easilytranserable (as it is oten developed or local ma-terials and climatic conditions). The support condi-tions used in catalogue designs also need to beanalysed on the basis or which the design optionswere developed. Catalogue designs are thereore

o little use or pavement rehabilitation.

Based on experience, structural coecients havebeen developed or certain pavement materials oruse in structural design. The AASHTO 1993 pave-ment design method uses a structural number thatis determined by summating the product o thesestructural coecients and the respective layerthickness. I the total exceeds a certain minimumnumber or the specic subgrade condition andstructural capacity requirement, the pavementstructure is considered to be adequate.

The Structural Number (SN) approach is simpleas it uses known materials with a track record operormance in given climatic conditions. Cautionshould be exercised when using this methodwhere climatic conditions are severe or wherelocal materials are signicantly dierent. Further-more, since there is no inherent control system ormaintaining pavement balance in terms o relativestiness o overlying layers, this design method isnot recommended or pavements with a struc-tural capacity requirement in excess o 10 millionESALs.

2.6.2 Catalogue design methods

2.6.3 Structural number method

Structural number calculation example

Pavement Layer thicknessSN layer

Layers Material mm inchesAsphalt 0.4

0.14

0.12

100

200

300

4

8

12

1.6

1.12

1.44

GCSCBR > 80

Naturalgravel

CBR > 45

Subgrade> 15

SN = 4.16

Structural

coecient

(per in)


66/369

2.6.4 Pavement number method

This method is similar to the structural numbermethod, but uses the eective long term sti-ness (ELTS) values or dierent pavement materi-als in place o structural coecients.This design method (described in TG2 (2009)) isbased on the analyses o long term pavement

perormance (LTPP) exercises combined withlaboratory research and heavy vehicle simulator(HVS) trials.

The pavement number method summates theproduct o the ELTS value and the respective layerthickness. The number obtained is then used in arontier curve (derived rom the LTPP exercise)to indicate the structural capacity o the pavementstructure.

As with structural numbers, the pavement number(PN) method is simple to use. The main dierencebetween the two methods is the procedure ol-lowed in determining appropriate ELTS values asopposed to selecting a structural coecient. Thisprocedure includes a comprehensive classica-

tion system or the materials in the various layersand takes into account the climate, the locationo the layer within the pavement structure and theamount o cover over the subgrade. It utilises themodular ratio rule to ensure pavement balance.

Dierent material classes and their respectivemodular ratio / maximum allowable stiness valueare summarised in the table below (see also TG2(2009)).

* These maximum stiness values are relevant only to the empirical Pavement Number model.

They are not intended as input or mechanistic models (see Section 4.3.12)

Material type ClassPrincipal strength

characteristicModular ratio

Maximum stiness

(MPa) *

HMA AC Marshall 5 2500

Bitumen stabilisedBSM

Class 1ITSDRY > 225 kPaITSWET > 100 kPa

3 600

Cement stabilisedCTB

Class C31.5 < UCS < 3 MPa 4 550

Crushed stone

G1

CBR > 100

2.0 700

G2 1.9 500

G3 1.8 400

Natural Gravels

G4 CBR > 80 1.8 375

G5 CBR > 45 1.8 320

G6 CBR > 25 1.8 180

G7 CBR > 15 1.7 140

Soils

G8 CBR > 10 1.6 100

G9 CBR > 7 1.4 90

G10 CBR > 3 1.2 70


67/36964 //65

Pavement Numbers may be used with condenceto design pavements with a structural capacity upto 30 million ESALs, the limit o the rontier curve.This is an articial limit since it is dictated by themaximum trac volume carried on pavements thatwere included in the LTPP data set. As this data

set is expanded and updat

Documents

Manual Wirtgen