ITF research reports long life surfacings for roads field test results

14 Summary of Phase 2: Laboratory testing of epoxy asphalt and high-performance cementitious materials .... Abbreviations AADT Annual average daily traffic BBTM Beton bitimineux très min

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ITF Research Reports

ITF Research Reports are in-depth studies of transport policy issues of concern to ITF member countries They present the findings of dedicated ITF working groups, which bring together international experts over a period of usually one to two years, and are vetted by the ITF/OECD Joint Transport Research Committee Any findings, interpretations and conclusions expressed herein are those of the authors and do not necessarily reflect the views of the International Transport Forum or the OECD Neither the OECD, ITF nor the authors guarantee the accuracy of any data or other information contained in this publication and accept no responsibility whatsoever for any consequence of their use This document and any map included herein are without prejudice to the status of or sovereignty over any territory, to the delimitation of international frontiers and boundaries and to the name of any territory, city or area

Foreword

This report is the third phase of an important research project that began in 2002 Taken as a whole, the project was designed to address the issues of road maintenance and the potential of long-life wearing courses to increase the longevity of a road The project is genuine research work at the forefront of road construction technology and is the fruit of the collaborative efforts of experts representing 12 countries This report summarises the results of field trials of two innovative materials for road surfacing

This project has been possible thanks to the dedication of the experts of the working group and their colleagues at testing laboratories, to the audaciousness of road owners who made it possible the construction of road sections with these two materials, to the engineers who worked on the fine-tuning of the mixes, and to the construction site teams who worked very hard, sometimes night and day, on the laying out of the courses with tight timing constraints The ITF would like to express, in particular, its gratitude to the following organisations and agencies, without which such an innovative research project could not have been undertaken:

• Agence Nationale de la Recherche (France)

• Conseil Général de la Sarthe

• Conseil Général de Loire Atlantique

• URS Infrastructure & Environment UK Limited

The ITF would also like to express its gratitude to the main authors of this report: Mr Finn Thøgersen (Danish Road Directorate, Denmark) and Mr Richard Elliott (URS Infrastructure and Environment UK Limited), respectively co-ordinators of the HPCM and epoxy-asphalt trials, and Mr François de Larrard (IFSTTAR and Lafarge, France), Chairman of the Working Group

Table of contents

Abbreviations 9

Executive summary 11

Chapter 1 Increasing the longevity of wearing courses 13

Summary of Phase 1: Economic evaluation of long-life pavements 14

Summary of Phase 2: Laboratory testing of epoxy asphalt and high-performance cementitious materials 15

Objectives of the field trials (Phase 3) and working method 19

Monitoring of the trial sections 19

Content of the report 21

References 22

Chapter 2 Epoxy-asphalt road surfacing field trials 23

Plant trials of epoxy asphalt in France 24

Field trials of epoxy asphalt open graded porous asphalt in New Zealand 25

Field trials of stone mastic asphalt and epoxy asphalt in the United Kingdom 34

Assessment of performance 45

Recommendations 46

Summary and conclusions 47

References 50

Chapter 3 Field trials with high-performance cementitious materials 53

Trials of HPCM in the United Kingdom 54

Trials of HPCM in France 56

Assessment of performance 64

Recommendations 64

Summary and conclusions 65

References 66

Working Group members 67

Figures Figure 1.1 Principle of the HPCM pavement 18

Figure 2.1 Two components of epoxy-asphalt binder 26

Figure 2.2 General view of the site 27

Figure 2.3 Start of the 20% EMOGPA section 28

Figure 2.4 Compaction of 20%EMOGPA 28

Figure 2.5 Traffic damage to 30% EMOGPA (plucked chip outside wheel tracks) 29

Figure 2.6 Curing of field trial specimens 30

Figure 2.7 Start of 30% air voids content EMOGPA section, looking towards 20% air voids content OGPA section 32

Figure 2.8 Start of 20% air voids content EMOGPA section, looking towards 30% air voids content EMOGPA section 32

Figure 2.9 Mean noise levels for cars, dual-axle and multi-axle trucks (SPBI =Statistical Pass By Index (according to ISO 11819-1)) 33

Figure 2.10 Composition of SMA mixture 36

Figure 2.11 General view of plant setup (bitumen delivery system on left) 37

Figure 2.12 Failed patch reinstatement typical of pre-trial condition 38

Figure 2.13 Paving of epoxy asphalt with conventional plant 39

Figure 2.14 Epoxy-asphalt trial section after 12 months trafficking (2013) 42

Figure 2.15 Mean stiffness (ITSM) data at three temperatures, performed on in situ cured cores, 13 months after production 43

Figure 2.16 Mean stiffness (ITSM) data at 20°C, performed on laboratory cured cores, at various ages after production 44

Figure 3.1 Equipment used for the HPCM laying 55

Figure 3.2 Machines developed for laying HPCM 56

Figure 3.3 Construction of the HPCM in Brettes-les-Pins 57

Figure 3.4 Aspects of the surfacing of the HPCM section in Brette-les-Pins 58

Figure 3.5 Construction of the HPCM section in St Philbert (France) 62

Figure 3.6 Skid-resistance of GFRUHPC, as measured with the Wehner & Schulze machine 63

Figure 3.7 Noise generation as measured by the CPX method on the St Philbert test section after two weeks of traffic 63

Tables Table 1.1 Monitoring requirements before, during and after the construction of the trial sections 20

Table 2.1 Mixture design for field trial 26

Table 2.2 Air temperatures near to trial site (December 2007–March 2010) 30

Table 2.3 Rutting 31

Table 2.4 Skid resistance (British Pendulum Number) 31

Table 2.5 Water permeability 33

Table 2.6 Mixing temperature and maximum usable life of epoxy asphalt 39

Table 2.7 Summary of skid resistance, texture and rut depth data 41

Table 2.8 Mean tensile strength (ITST) data at 20°C at various ages after production 44

Table 3.1 HPCM mix-composition 60

Abbreviations

AADT Annual average daily traffic

BBTM Beton bitimineux très mince (Very thin asphalt concrete)

CPX Close proximity method to measure noise level

EA Epoxy-asphalt

EMOGPA Epoxy-modified open graded porous asphalt

FWD Falling weight deflectometer

GFRUHPC Grooved fibre-reinforced ultra-high performance concrete

HPCM High-performance cementitious material

IRI International rutting index

ISO International Organization for Standardization

ITST Indirect tensile splitting strength

OGPA Open graded porous asphalt

PVA fibres Poly(vinyl alcohol) fibres

SCRIM Sideway-force Coefficient Routine Investigation Machine

SMA Stone mastic asphalt

Executive summary

Background

Maintenance of high-traffic roads is expensive, and has indirect social costs that are less and less acceptable in the context of traffic gridlock in big cities Therefore, a shift from low cost, low durability maintenance techniques to more durable and more expensive ones is desirable for the sake of the common interest The long-life pavement (LLP) project launched by the ITF in 2002 addressed these issues in a series of three reports of which this is the final one

The first phase of the project focused on the economics of road surface maintenance It concluded that for a sufficient level of traffic, long life wearing courses would be globally sustainable at a life expectancy of 30 to 40 years, with a total cost less than three times that of current techniques Two families of material – epoxy asphalt and high performance cementitious material appeared to have the potential for this and a number of countries involved in the project commissioned their national road laboratories to investigate this question

During the second phase of the project, nine countries joined efforts to study two potential solutions The first one was of the bituminous type: epoxy-asphalt (EA) This material has a good record in the field of long-span steel bridge decks Extensive testing in the laboratory as well as in accelerated loading tests (ALT) gave a positive appraisal of this material’s potential use in longer road sections submitted to heavy traffic The second, more innovative technique underwent laboratory tests for the first time as part

of the the project This high-performance cementitious material (HPCM) consists of a surface dressing with hard, polishing-resistant chippings embedded in a thin layer of ultrahigh-performance, fibre-reinforced mortar HPMC’s mechanical properties proved to be as encouraging as the alternative solution

The third phase consisted of full-scale field tests These field trials were carried out between 2009 and 2012 in three of the participating countries, France, New Zealand and the United Kingdom

Findings

The epoxy-asphalt (EA) solution has so far met initial expectations Feedback from the UK and New Zealand test sites is encouraging, suggesting the transfer of this technology from bridges to pavements at an industrial scale seems possible

The HPCM solution is not yet at the same level of maturity The technique proved difficult to apply

in an industrial scale It also tends to create noisy pavements, which are becoming less and less accepted Grooved fibre-reinforced ultrahigh-performance concrete (GFRUHPC) seems more promising, but needs further development to achieve full control of production and placement Specifically, issues like shrinkage-induced cracking need to be mastered Once optimised, the quality of the material should provide road owners with an alternative, long-life and sustainable road surfacing option

The short, experimental test sections built during Phase 3 did not allow a sound economic assessment of what could become a mature technique Even if the economic justification can be only demonstrated through a tender process looking at whole-life costs, it is likely that the recommended

techniques could meet the goal of keeping a total cost at less than three times the cost of current solutions

Policy insights

Long-life surfacing is essential for advanced and affordable transport infrastructure

A long-life surfacing is an essential requirement for the advanced and affordable transport infrastructure envisaged by the Forever Open Road (FOR) concept Long-lasting overlays as part of durable and integrated pavements are one of the key research and innovation themes of FOR in order to produce an affordable road for a society that cannot afford road closures

The higher cost of long-life road surfacing materials is justified particularly for road network hot spots

While the additional cost and marginally increased construction complications will limit the use of advanced long-life road surfacing materials for many conventional applications, the justification for advanced surfacing materials can only increase as traffic levels continue to rise In certain road network hot spots where any loss of serviceability is unacceptable, they will be the material of choice

It will be important to continue monitoring existing test sections in the future to corroborate

findings over the road pavement life cycle

In 2025, the test sites in the UK and New Zealand will have reached about 15 years of use; an age where normal wearing courses are reaching the end of their life cycle It is recommended to continue with site visits to obtain further corroboration regarding the usefulness of this technique Research on potential health issues related to the use by epoxy binders should continue in the light of concerns in some countries regarding the application of epoxy binders on site

Chapter 1 Increasing the longevity of wearing courses

This chapter summarises the results of the two first phases of the project: the study on the economic viability of long-life wearing courses and the laboratory testing of candidate materials for long-life surfacing It presents the objectives of the third and final phase of the project: the full scale field tests of two candidate materials (epoxy asphalt and high performance cementitious material)

Maintenance and rehabilitation of existing roads constitute a permanent challenge for road administrations and an increasing part of their budget In 2011, the share of public expenditure on road maintenance represented between 25% and 35% of total road expenditure (ITF, 2013) These costs do not take into account user costs due to disruption and congestion, which also increase and are of particular concern for heavily trafficked roads

In periods of budget pressure that affect many ITF countries, savings on public expenditures and user costs to maintain the road infrastructure would be welcome It is in this context that the notion of

“long-life pavements” started to interest policy makers Long-life pavements would be expected to show high quality performance without the need for significant repair for more than 30 years and, under certain conditions, the benefits of avoiding major repairs and re-pavements may become large enough to justify the higher initial costs of such pavements

It has been demonstrated that long-life as just described is achievable for the subsurface pavement layers, but the surface layer or wearing course, which is critical for safe and comfortable driving, remains the Achilles’ heel of the concept This thin uppermost pavement layer is, more than any other part of the structure, exposed to air, sun and weather, and to the wear, tear and deformation from the traffic it carries

Today, pavements with bitumen or cement binders dominate the market They function well in a wide range of traffic and climate conditions and have few environmental disadvantages However, although quality products are available, most pavements exhibit shortcomings in terms of durability, road-user qualities, strength and repair needs This translates into poor maintenance economy when these pavements face the challenge of the increasing vehicle-mass limits and higher density of traffic on the arterial roads of today and the near future

It is in this context that the OECD decided to launch in 2001 a major research project to develop a new long-life pavement surfacing This project was conducted in three distinct phases:

Phase 1 (2001-2003): Economic viability of long-life wearing courses and identification of

candidate materials for long-life surfacing

Phase 2 (2005-2007): Laboratory elaboration and accelerated load testing of suitable candidate

materials

Phase 3 (2009-2013): Field tests of the selected materials

This 12-year project ended in 2013 after two to six years monitoring of the trial sections This report presents the detailed results of the field tests, including the preparatory work, the construction phase and the monitoring phase, and presents the final conclusions of the project

Summary of Phase 1: Economic evaluation of long-life pavements

European Conference of Ministers of Transport (ECMT, 2005) assessed the likely envelope of costs for economic viability of new long-life wearing courses, taking into account all the costs involved including initial construction costs as well as savings in maintenance costs and user cost savings expected in the longer term

Phase 1 provided guidelines for a research programme to assess the real capacity of the candidate materials and their suitability as long-life wearing courses and recommended to undertake laboratory testing on both materials (Phase 2)

From a cost viewpoint, Phase 1 concluded that long-life pavement surfacing costing around three times that of traditional wearing courses per square metre would find a market for a range of high-traffic roads, depending on an expected life of 30 years, discount rates of 6% or less and an annual average daily traffic (AADT) of 80 000 or more with at least 15% of heavy trucks

A review of advanced surfacing materials confirmed that that there were indeed materials that could

be feasible for long-life surfacing and from the review of materials it was concluded that two types of materials in particular had the potential to fulfil the requirements: epoxy asphalt and high-performance cementitious materials (HPCM)

Epoxy asphalt

Epoxy asphalt is a premium material, which has been used for many years as a road surface on stiff bridge decking The first such application, on the San Mateo Bridge (California, United States), is still meeting performance requirements, after 40 years of service Over time, epoxy asphalt has been more widely used for stiff bridge decking applications in a number of other countries

Administrations have not used epoxy asphalt for regular road pavement surfaces as cheaper materials have been available which, although they may not last as long, could be replaced relatively easily and each time at moderate cost

High-performance cementitious materials

In the last years of Phase 1, there were already references to cementitious materials which exhibited superior strength and durability properties For instance, the family of ultra-high-performance fibre-reinforced concrete was gaining recognition, and recommendations were released in 2004 to practical applications, mainly in the precast concrete industry or for some special, niche markets Therefore it was stated that such solutions could be studied for the pavement domain, even if the material would need substantial adaptations to match the specifications of a road wearing course A new solution, proposed for the next project phase, was entitled high-performance cementitious material (HPCM)

It is an innovative product which was developed and tested for road surfacing applications for the first time during this project This pavement surfacing consists of a layer of ultra-high performance, fibre-reinforced fine mortar, in which hard, polish resistant aggregate particles are embedded

Summary of Phase 2: Laboratory testing of epoxy asphalt and high-performance cementitious materials

The objective of the second phase of the project (ITF, 2008) was to research the behaviour and properties of the materials identified as candidates and test them sufficiently to assess their suitability for use in long-life wearing courses Co-ordinated testing, including accelerated load tests, was conducted to assess the durability and other essential properties identified for long-life wearing courses These tests were done in the following national testing laboratories:

• Australia: New South Wales Roads and Traffic Authority

• Denmark: Danish Road Institute and DBT Engineering

• France: Laboratoire Central des Ponts et Chaussées (LCPC, now known as IFSTTAR, for

Institut Français des Sciences et Technologies de l’Aménagement et des Réseaux)

• Germany: Federal Highway Research Institute (BASt)

• New Zealand: Transit New Zealand (now known as The New Zealand Transport Agency) and Opus International Consultants Ltd

• United Kingdom: Transport Research Laboratory (TRL) Ltd, Scott Wilson (now URS Infrastructure and Environment UK Limited) and the Highways Agency

• United States: Turner Fairbank Highway Research Center

Main findings regarding epoxy asphalt

On the basis of the comprehensive testing undertaken, acid-based epoxy-asphalt mixtures were found to have greatly improved performance compared to conventional mixtures In particular, compared

to conventional asphalts, cured epoxy asphalts are significantly:

• stiffer (higher modulus) at service temperatures, with greater load-spreading ability

• more resistant to rutting

• more resistant to low temperature crack initiation

• more resistant to surface abrasion from tyre action, even after oxidation

• more resistant to fatigue cracking (although the benefits are less marked at higher strain levels)

• less susceptible to water induced damage

• more resistant to oxidative degradation at ambient temperatures

A limited accelerated pavement testing (APT) trial of epoxy-modified open graded porous asphalt (OGPA) resulted in early signs of surface abrasion in the control section but not in the epoxy one Tests

on the APT sections demonstrated that the skid resistance of epoxy asphalt was not significantly different from that of conventional asphalt

The tests undertaken confirmed that epoxy asphalt is a premium material that outperforms conventional binders Test performance of the epoxy-asphalt materials studied in Phase 2 was considered greatly superior when compared with conventional materials, on the important indicators central to assessment of the potential for long service life

Performance expectations for the longevity and durability of epoxy-asphalt surfaces were built up during the project taking into account the results of the tests undertaken and experience with their relationship to longevity in the field Nearly all the testing has indicated that epoxy asphalt should provide a durable long lasting surfacing, even in the most heavily trafficked road situations

The tests undertaken showed the type of epoxy materials and the choice of aggregates had an important impact of the performance of the surfacing In addition, epoxy asphalt needs close supervision

at time of production and laying to ensure full mixing is achieved; time and temperature need to be carefully monitored to achieve the best performance outcomes

Phase 2 recommended that further research work be undertaken, in particular on the following aspects:

• Curing and construction time Further laboratory studies are needed prior to any demonstration projects to optimise the curing profile with the desired rate of reaction for the local conditions (for example, time for curing, distance of transport and laying)

• Curing period It is important to establish when after the initial blending of the epoxy asphalt the reaction is complete

• Curing temperature Some epoxy systems have shown the ability to cure rather rapidly at a lower temperature than might be expected The prospects for lower temperature curing – and the related potential for energy and cost savings during production – need further research

• Production process: Epoxy asphalt is a material with high stiffness that can be applied in thin surface layers Production experience to date for the relatively small quantities used has almost exclusively been with a batch plant that gives good control of mixing time – an important part of its subsequent curing and post-curing properties However, for the trials in New Zealand a continuous mix drum plant was used without problems

• Construction process: Due to the thermosetting nature of the material, extra care is required

in the timing of manufacturing and construction phases to ensure the product is not cured before compaction The risk of construction failures and damage to plant is greater than with conventional bitumen For both these areas, the perceived risk is likely to diminish in importance as experience with the material grows

over-• Health impact: When uncured, certain epoxy materials contain compounds harmful to people and the environment These were not used for the epoxy asphalts in this project However, if such materials are used, special equipment and safety precautions would be required for all involved in handling them while uncured

In summary, Phase 2 concluded that if all aspects of the process are correctly handled, epoxy asphalt should be able to provide a surfacing material that can be expected to meet the aim for a much extended, practically maintenance-free life, i.e 30 years or more It was recommended to undertake field tests to further analyse and research the areas above mentioned before making general recommendations

on the future use of this material for long-life surfacing

Main findings regarding high-performance cementitious material

High-performance cementitious material (HPCM) is an innovative product developed by the Working Group and tested for road surfacing applications for the first time during this project The initial mix design was improved during the project It evolved through a number of stages which included: selection of constituents, mix design and laboratory application processes and assessment of behaviour It was assessed against critical properties such as: strength and abrasion resistance, E-modulus, coefficient

of thermal expansion, bond with the bituminous substrate, cracking behaviour, skid resistance and durability in harsh environment

Overall, the thickness of the fibre-reinforced mortar layer needed to be minimised for cost reasons

At the same time, it needed to be thick enough to allow for good penetration of the chippings in the fresh mortar The test programme focussed on the following performance issues:

• general physical properties of HPCM particularly in regard to bond to substrate and capability to establish a lasting bonding of chippings to the matrix

• ductility and fatigue properties

• durability under environmental impact

• surface properties, noise and skid resistance

By comparison with epoxy asphalt, the HPCM solution needed more development, including operational laying techniques, before being ready for commercial introduction as a long-life surfacing However, the tests undertaken in Phase 2 indicated there is a high probability that the current uncertainties about HPCM applications will be overcome

Figure 1.1 Principle of the HPCM pavement

Source: Laboratoire Central des Ponts et Chaussées

A number of issues were identified for future research and testing, including:

• Effect of water dosage on HPCM properties The water dosage has a significant impact on mortar engineering properties, such as: ease of mixing (at industrial scale) and workability; chippings loss, and; bond with the asphalt

• Industrial application technology The adaptation of existing equipment or the practical development of new pavement laying equipment was a high priority for the Phase 3 field testing

• Two-dimensional cracking tendency The test pad chosen for testing two-dimensional cracking tendency needs to be fully representative of a real pavement and laid on a sufficiently stiff asphalt material

• Production of HPCM Production is seen as a manageable process using existing know-how and equipment However, some modification of existing equipment or development of new equipment will be required for laying the HPCM mortar and inserting the chippings Construction factors that are important include the availability of constituent materials, the mixing process and the workability of the freshly mixed material The application of the chippings should ideally take place immediately after placing the thin mortar layer, i.e with the same machine or with a chip spreader A light rolling or tamping action is required to ensure the desired embedment of the chippings and a flat, even running surface

Based on the test results, Phase 2 concluded that if the HPCM layer performs well for the first one-two years, then it is unlikely to fail in the following years It is the expectation that this surface, based on further trials, can be developed into a final product characterised by high safety, comfort, durability and limited noise emission Because HPCM is a full innovative concept, further work and research is needed to test in real conditions, in particular the production process

Objectives of the field trials (Phase 3) and working method

The research in Phase 2 provided comprehensive results from laboratory testing and trials in various accelerated pavement testing machines The expectations for the durability and long-life capabilities of the materials were based on extrapolations of observations made during this testing The innovation process naturally requires that the materials be tested in larger scale under real traffic and environmental conditions In particular, the aims of the field tests were to:

• confirm the performance of the two materials under real traffic and environmental conditions

• develop construction methods

• improve cost estimates

• optimise material mixes

• increase contractor experience levels

A Working Group composed of experts from 11 countries was in charge of co-ordinating field trials undertaken by voluntary countries Although interest in the construction and monitoring of trial sections

in a joint research effort was initially expressed by several countries, a number of factors, including the impact of the post-2008 global financial crisis, made locating funding and stimulating an appetite to trial new materials extremely difficult Nevertheless, five road sections were built using the innovative materials Sites using epoxy asphalt:

• New Zealand: two 60 m long sections in Christchurch, built in 2007 (yet during Phase 2 of the project)

• New Zealand: three 210 m long sections in Christchurch, built in 2012

• The United Kingdom: a 110 m long section near Truro (in Cornwall), built in 2012

• Sites using HPCM:

• France: a roundabout near Le Mans, built in 2010

• France: a 150 m section, near Nantes, built in 2011

In addition, some further laboratory testing on HPCM was also conducted in the United Kingdom and in Belgium to further develop the HPCM mix and the pumping equipment; and tests were also conducted in Germany and France on epoxy asphalt

Monitoring of the trial sections

The five trial sections were regularly monitored On each site, an idealised set of data and information to be collected before, during and after the construction phase was agreed (Table 1.1), although individual countries were free to interpret these requirements as appropriate for their local situations

Table 1.1 Monitoring requirements before, during and after the construction of the trial sections

Preparation of the trial • Visual condition survey

• Structural assessment

• Evenness of the base course

• Traffic assessment

Construction phase • Temperature and weather conditions

• Material QC data (mix-design, material properties)

• Site schedule (production and laying rates)

• Unexpected events (problem identification and management)

Immediately after the construction and before

ravelling/aggregate loss and cracking)

• Profile (longitudinal/transverse), IRI, rutting

• Texture depth (EN 13036-1)

• Skid resistance (e.g portable skid resistance tester according to EN 13036-4 and/or measurement vehicle)

• Noise measurement (e.g SPB according to ISO Standard 11819-1 or CPX according to ISO/CD 11819-2)

ravelling/aggregate loss and cracking)

• Profile (longitudinal/transverse), IRI, rutting

• Texture depth (EN 13036-1)

• Skid resistance (e.g portable skid resistance tester according to EN 13036-4 and/or measurement vehicle)

• Noise measurement (e.g SPB according to ISO Standard 11819-1 or CPX according to ISO/CD 11819-2)

Specific monitoring regarding HPCM • Assessment of HPCM thickness at the fresh

state (during trial)

• Photo documentation of aggregate spreading procedure and result

• Removal of a few cores for documentation of layer thickness

• Special attention during visual condition surveys to possible delamination and end joint problems

Content of the report

This report describes each field test and summarises the findings It is composed of the following chapters:

• Chapter 2 describes the experiences with the epoxy asphalt sites in New Zealand and the United Kingdom

• Chapter 3 describes the experiences with the pad tests in the United Kingdom and the two HPCM sites in France

• Chapter 4 presents the general conclusions from the trials and the recommendations from the Working Group on the potential of long-life pavement surfacing

Chapter 2 Epoxy-asphalt road surfacing field trials

This chapter describes the findings of the third phase of this project (i.e the field trials) in respect

to the epoxy-asphalt materials tested Three test sections using epoxy asphalt were built and monitored: two in epoxy-modified open graded porous asphalt, in New-Zealand, and the third one

in stone-mastic asphalt, in the United Kingdom No significant difficulties were encountered during the construction phase, and the two pavements have exhibited to date satisfactory behaviour under service

The overall objective of Phase 3 was to demonstrate that the performance envisaged from the laboratory and accelerated testing would hold true within the period of the trial under real traffic and environmental conditions Additional aims were to develop construction methods, optimise mixtures, and increase contractor experience As in Phase 2, the research approach taken in the epoxy-asphalt group was to have participating organisations identify and utilise local sources of epoxy asphalt and compare the characteristics and performance results with those of a standard high quality reference material In conducting the comparison, the epoxy-asphalt binder would replace the bitumen in the reference material and other aspects of the selected system would remain the same Adopting this approach allowed the participating countries to focus on their likely application of epoxy asphalt using local materials and standard test procedures, while providing a qualitative assessment of actual field performance

Epoxy-asphalt surfacing systems are not new Pioneering work was done by Shell in the 1950s, initially to develop surfaces to resist jet fuel damage and as a heavy duty surfacing in industrial areas Epoxy asphalt was also used at the time for a limited number of highway applications, but it was particularly adopted as a thin, stiff surfacing on steel bridge decks, where the material has been used on a number of major bridges around the world Excellent performance has been recorded, most notably on the San Mateo-Hayward Bridge, where epoxy-asphalt surfacing has been in service for more than

45 years without failure (Lu et al., 2012) Due to its superior resistance to aircraft fuel and jet-blast, the material has also been used on a number of military airfields in the United States (Simpson et al., 1960) Prior to the current project, the main use of epoxy asphalt in the United Kingdom in recent times had been on a limited number of steel bridge decks (Erskine and Humber), where the design was based on hot rolled asphalt To the authors’ knowledge, except as mentioned above, epoxy-asphalt surface course has not been used to any significant degree for highway surfacing However, as part of the current project, successful trials of epoxy-modified materials have been carried out on live road sites in New Zealand and the United Kingdom and initial indications from these trials are very encouraging

Interest in participating in a joint research effort was initially expressed by national institutions from nine countries: France, Germany, Israel, New Zealand, Norway, South Africa, Spain, United Kingdom and the United States Unfortunately, a number of factors, including the impact of the post-2008 global financial crisis, made locating funding and stimulating an appetite to trial new materials extremely difficult Therefore, only France, New Zealand and the United Kingdom were able to play an active role

in the field trials of the epoxy-asphalt material In the event, for a number of practical reasons, France was able to complete plant trials only However, as part of the current project, successful trials of epoxy modified open graded porous asphalt were carried out in New Zealand (Herrington, 2010), and of epoxy-modified stone mastic asphalt in the United Kingdom

Plant trials of epoxy asphalt in France

In 2009, France selected a site near Le Mans and carried out laboratory trials of typical French mixtures manufactured with an amine curing type of epoxy modified bitumen, a proprietary product supplied by the contractor The binder was described as 20% epoxy (component A) and 80% bitumen (component B) of 80-100 penetration grade Seven binders were investigated in order to try to identify a very slow (amine) curing epoxy This work revealed that the curing time of the premixed components (A+B) was critically dependent on mix temperature, and the “workability window” reduced from four hours at a mix temperature of 120°C to 1.5 hours at a mix temperature of 140°C

The contractor planned to produce the epoxy modified material through a turbulent-mass drum mix plant (continuous type) However, it proved difficult to ensure that precise quantities of each component were added using this type of mixing process and that the temperature within the mixing drum were maintained at 120°C Cleaning the epoxy binder distribution system was also an issue Although the use

of a batch mixing plant was envisaged, the trials were finally aborted due to these technical risk concerns

Field trials of epoxy asphalt open graded porous asphalt in New Zealand

Research outline

The New Zealand Transport Agency’s (NZTA) contribution to the research focused on the potential benefits of epoxy-modified open-graded porous asphalt (EMOGPA), specifically to undertake the construction of a full-scale road trial and monitor its performance A summary of this work is provided below; full details have been provided by Herrington (2010)

Although the safety and noise-reduction properties of open-graded porous asphalt (OGPA) are well documented, binder oxidation is a major problem and is the principal factor governing the ultimate life of porous asphalt Because of the very open nature of the material, oxidation and consequent binder embrittlement are more rapid than in conventional mixtures Oxidation ultimately leads to failure of the mixture through loss of material from the surface (ravelling or fretting) under traffic-shearing stresses The result is a reduced life compared with denser mixtures, adversely affecting their cost-benefit ratios and thus inhibiting the more widespread use of this safe and environmentally friendly surfacing

EMOGPA appears to offer the potential for a significant improvement in life for open-graded surfacing EMOGPA uses the same mixture designs as conventional OGPA, but the bitumen component

is replaced with a bituminous binder incorporating a reactive epoxy resin and curing agent

Design

The road trial was laid on the outer north-bound lane of Main North Road (part of State Highway 1)

at Belfast in Christchurch on 5 December 2007 The trial site consisted of three sections A standard

PA 14 OGPA, meeting NZTA Specification P/11 (NTZA, 2007) was used as a control and a 20% air voids content EMOGPA and a 30% high air voids content EMOGPA were laid The 30% air voids content epoxy asphalt represented an attempt to match the highest air voids content achieved with polymer-modified conventional OGPAs – such 30% air voids mixtures have been noted as having particularly good acoustic performance

The site had an unbound granular pavement foundation, with 15 850 vehicles per day heading north,

of which 6% were heavy commercial vehicles The three sections were contiguous, each 60 metres long,

5 metres wide and 30–35 mm thick Looking north, the order of the sections was 20% EMOGPA, 30% EMOGPA and 20% control OGPA The trial site was in the outer of the two lanes heading from the city, where an existing OGPA laid in 1992 was being replaced because of fretting The inner lane was laid using standard 20% OGPA Falling weight deflectometer (FWD) testing suggested that the site was structurally sound The existing OGPA surface of the site was milled out and a grade 5 (10 mm) chipseal was constructed over the remaining thin asphaltic concrete surfacing

Materials

The epoxy bitumen used was supplied by ChemCo Systems Ltd of California This is a two-part product that is blended just before use (Figure 2.1) Part A (used at 14.6% by weight) consists of an epoxy resin formed from epichlorhydrin and bisphenol-A Part B type V (85.4%) consists of a fatty acid curing agent in an approximately 70 penetration grade bitumen The bitumen used for all control mixtures was an 80–100 penetration grade bitumen, manufactured from Middle Eastern crudes,

comprising both air-blown and butane-precipitated material, and conforming to the NZTA M/1:2011 specification (NTZA, 2011) This bitumen is commonly used in OGPA surfacing in New Zealand

Figure 2.1 Two components of epoxy-asphalt binder

Source: Turner-Fairbank Highway Research Center, USA

The mixture designs (grading, aggregate source and binder content) were nominally the same as those used in the laboratory work reported in Phase 2 Compaction of 100 mm diameter specimens for testing was by Marshall Hammer (75 blows per side) and carried out at the Fulton Hogan Ltd laboratory

in Christchurch, according to ASTM D6926 (ASTM, 2004) Production testing of the mixtures gave the results shown in Table 2.1

Table 2.1 Mixture design for field trial

Test section Passing (%) sieve size (mm) Bitumen

content (%)

Air voids content (%)

Manufacture and construction

A turbulent-mass continuous-mix drum plant was used to manufacture the EMOGPA An in-line blending system was used to introduce the epoxy binder Epoxy component A, heated to 85°C, entered the line carrying component B (120°C) about 4 metres from the point of discharge into the drum to

provide premixing of the two components Ordinary positive displacement gear pumps fitted with electronic mass flow meters were used The flow metres reported to the plant control system controlling the pumps The epoxy-asphalt mixtures were held at 125°C for 45 minutes before compaction

The epoxy mixtures were manufactured first; the first four-five tonnes of the control mixture that followed was run through and then discarded, in order to clean the plant When the manufacture of the asphalt was complete, the pumps and lines used to introduce the epoxy bitumen components were disconnected from the plant and drained and flushed with bitumen and kerosene Manufacture of the epoxy mixture was found to be straightforward and completed without difficulty, except for the unanticipated drain-down of the 30% EMOGPA

Figure 2.2 General view of the site

Source: NZTA (New Zealand)

Construction and compaction by a standard tandem steel-wheel vibratory roller required about 20−30 minutes for each section Temperatures during compaction were 55−70°C for the epoxy mixtures The total time from the commencement of the manufacture of the first epoxy mixture to the commencement of construction was 45−60 minutes The mixture was manufactured at a temperature of 117°C and 122°C for the 30% and 20% sites respectively

There were some problems in compaction of the EMOGPA, particularly the 30% material, because

of concern that the epoxy might cure before compaction occurred Although the initial viscosity of the epoxy binder is somewhat lower than that of 80−100 bitumen at the same temperature, when excessive curing occurs, the epoxy bitumen becomes “dry” and is not adhesive To increase the working-time, the period for which the mixture was held at high temperature was kept to a minimum Although this time was similar to that used in the laboratory work (45 minutes), a longer mixing time at high temperature in the plant, or a higher plant temperature, would have been desirable to increase the viscosity of the binder

As a result, there was some initial “pick-up” on the roller, and the road surface had to be cooled with water before traffic was allowed on it that afternoon The mixture at the 30% site was still “lively” some

three hours after compaction was complete Other than this, the behaviour and appearance of the EMOGPAs was indistinguishable from that of the control material No unusual fuming or smell was noted, as was also the case in the earlier CAPTIF trial (Herrington et al., 2007) Figures 2.2−2.5 show aspects of the trial construction The trial sections were opened to traffic that afternoon

Figure 2.3 Start of the 20% EMOGPA section

Source: NZTA (New Zealand)

Figure 2.4 Compaction of 20%EMOGPA

Source: NZTA (New Zealand)

Figure 2.5 Traffic damage to 30% EMOGPA (plucked chip outside wheel tracks)

Source: NZTA (New Zealand)

Curing of the EMOGPA

The rate of curing of the EMOGPA was monitored by measuring the indirect tensile modulus of

100 mm diameter cylindrical blocks (in triplicate) prepared at the time of construction and placed outside

at the Fulton Hogan Ltd laboratory (Pound Road, Christchurch), close to the trial site These blocks were wrapped in silicone release paper to help prevent deformation of the blocks, and were tested periodically

to determine the increase in modulus The modulus measurements were conducted on a 5 KN test frame

at 25°C, according to AS2891.13.1 (Standards Australia, 1995)

Data for the 20% air voids content EMOGPA (shown in Figure 2.6) suggested that it had cured rapidly over the first 30 days and the modulus was still increasing slowly beyond that The control modulus increased over the first summer but changed little thereafter The 30% air voids content EMOGPA modulus appeared to be unchanged The very open structure and low bitumen content meant these samples were very fragile, and it is not certain that they were representative of the in situ material The results for the 30% EMOGPA were also in contrast to those of the 25°C curing experiments carried out on the laboratory-prepared mixture, where a small increase was observed over 140 days at 25°C This could have been because the average road temperature was below 25°C, or more likely, the lower binder content (4%) compared with the 5% of the laboratory mixtures

The curing rate of the isolated blocks was likely to have been lower than that of the material on the road, where the greater mass could have acted to produce higher overall average temperatures Road temperatures were not measured directly; however, air temperature data from a weather station near the site (Christchurch Airport) are given in Table 2.2

Figure 2.6 Curing of field trial specimens

Table 2.2 Air temperatures near to trial site (December 2007–March 2010)

Average daily maximum 17.5

Average daily minimum 6.6

Assessment, testing and monitoring

The sites were monitored visually and vehicle noise was measured over three years Measurements were also made for rutting, skid resistance and water permeability every 10 metres, both inside and outside the wheel tracks (except for rutting) The general appearance of the site after three years is shown

in Figures 2.7 and 2.8

The surfaces were found to be in good condition, with the exception of small patches at the end of each of the EMOGPA sections (e.g lower edge of Figure 2.7), where some ravelling had occurred These patches corresponded to locations where the paving machine sat for long periods waiting for new material to lay, which appears to have caused damage Discolouration in these patches was apparent immediately after construction

Rutting

The 2-metre straight-edge rutting results in Table 2.3 show minimal rutting The results suggest that the epoxy sections were at least as strong as the control in early life, even without significant curing

Table 2.3 Rutting

January 2008 January 2009 March 2010

Table 2.4 Skid resistance (British Pendulum Number)

Section

British Pendulum Number ± 95% CL

Wheel tracks

Outside wheel tracks

Wheel tracks

Outside wheel tracks

Wheel tracks

Outside wheel tracks Control 53 ±2 51 ±2 59 ±2 63 ±3 50 ±2 55 ±5

20 % EMOGPA 50 ±2 45 ±5 52 ±2 56 ±3 48 ±2 56 ±6

30 % EMOGPA 53 ±2 49 ±3 57 ±2 61 ±3 49 ±2 57 ±3

Figure 2.7 Start of 30% air voids content EMOGPA section, looking towards 20% air voids content OGPA

section

Source: NZTA (New Zealand)

Figure 2.8 Start of 20% air voids content EMOGPA section, looking towards 30% air voids content

EMOGPA section

Source: NZTA (New Zealand)

Water permeability

The results from field water-drainage tests (using an in-house method based on NZTA P23:2005 specification,) detailed in Table 2.5, show that drainage times had increased, with the exception of the 30% air voids content material, which showed relatively little change and was the most free-draining of the three sites Data for 2010 for the control and 20% EMOGPA sites was an underestimate, as several readings were, in each case, greater than 100 seconds Measuring longer drainage times was not practicable with the method that was used

Table 2.5 Water permeability

Section

Mean water permeability (seconds) ± 95% CL

Wheel Tracks

Outside Wheel Tracks

Wheel Tracks

Outside Wheel Tracks

Wheel Tracks

Outside Wheel Tracks Control 22 ±13 20 ±14 33 ±13 34 ±28 >65* >41*

* Lower bound of real result – see text

Figure 2.9 Mean noise levels for cars, dual-axle and multi-axle trucks (SPBI =Statistical Pass By Index

(according to ISO 11819-1))

Noise

The results of noise measurements are shown in Figure 2.9 These show that all three sites generated similar levels of tyre noise Surprisingly, the 30% air voids content EMOGPA did not produce a noticeably quieter surface This may have been because of the problems associated with “pick-up” of the material on the roller during compaction and early trafficking, which may have led to more surface texture than would normally be expected, and hence higher noise levels, cancelling out the benefits of the higher percentage voids

The noise level had increased for all sites (between 2008 and 2009), consistent with the reduced water permeability measurements It had rained heavily the night before the January 2009 measurements were taken, and although the surface was dry, water may have still been present in the voids and affected the result It is interesting to note that there was no comparable increase in noise level between 2009 and 2010; more measurements are needed to properly assess trends

Laboratory work

During the same period that the field trial was being constructed and monitored, a programme of complimentary laboratory work was undertaken to investigate the curing behaviour and durability properties of EMOGPA, and to examine the effects of diluting the epoxy binder composition as a way of reducing costs A brief summary of this work is provided below

Open-graded porous asphalt (OGPA) specimens were treated in an oven at 85°C for up to 171 days, resulting in oxidation equivalent to approximately 20 years in the field Although the moduli (25°C) of both materials increased with oxidation time, that of the EMOGPA was much more pronounced, reaching 12 000 MPa after 171 days at 85°C, compared with 7 800 MPa for the control This time period results in oxidation considered to be equivalent to about 20 years in the field (80 days is considered to be equivalent to 12 years in the field) Data from storage in oxygen and nitrogen atmospheres suggested that the greater hardening of the EMOGPA is largely attributable to gradual curing, rather than to oxidation Despite the very high modulus, the Cantabro Test results showed that oxidation had no significant effect

on the abrasion resistance of the EMOGPA After 171days, the EMOGPA mass loss was within error of the initial value, whereas that of the control had increased by 1.8 times Similarly the fatigue life of oxidised EMOGPA was markedly greater (more than 25 times) that of the control

Dilution of the epoxy binder to 25% or 50% of the mixture binder composition, using the standard 80-100 penetration grade bitumen used in the control mixture, gave an OGPA mix with properties inferior to that of the undiluted material, but still markedly superior to conventional OGPA in terms of abrasion resistance after oxidation Cantabro Test losses for the 25% and 50% mixtures increased only 1.4 times after 171 days oxidation The fatigue life of the oxidised 25% and 50% EMOGPA mixtures were equivalent to that of the control For clarity, and as an example, the 50% EMOGPA mixture comprised 14.6 parts of epoxy component A, 85.4 parts of epoxy component B and 100 parts of 80-100 penetration grade bitumen It was noted that the usefulness of this approach may depend on the selection of the appropriate bitumen to ensure compatibility with the epoxy components, and may not be successful with all bitumens

Field trials of stone mastic asphalt and epoxy asphalt in the United Kingdom

In the United Kingdom, the Highways Agency (HA), an executive agency of the Department for Transport with responsibility for operating, maintaining and improving the Strategic Road Network in England, provided support to Scott Wilson (now URS) to assist in the organisation of the full scale