AP-T245-13

AP-T245-13

Maximising the Re-use of Reclaimed Asphalt Pavement: Binder Blend Characterisation

AUSTROADS TECHNICAL REPORT



Published August 2013

© Austroads Ltd 2013

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without the prior written permission of Austroads.

ISBN: 978-1-925037-18-0

Austroads Project No. TT1817

Austroads Publication No. AP-T245-13

Project Manager Andrew Papacostas, VicRoads

Prepared by Erik Denneman, Melissa Dias, Shannon Malone, Young Choi, Elizabeth Woodall, Robert Urquhart

ARRB Group

Acknowledgements The materials used in this study were supplied free of charge by the Alex Fraser Group,

BP Bitumen Australia, Curtin University, and Shell Bitumen. Their contribution is gratefully acknowledged.

Published by Austroads Ltd Level 9, Robell House 287 Elizabeth Street

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Sydney 2013

About Austroads Austroads’ purpose is to:

promote improved Australian and New Zealand transport outcomes

provide expert technical input to national policy development on road and road transport issues

promote improved practice and capability by road agencies.

promote consistency in road and road agency operations. Austroads membership comprises the six state and two territory road transport and traffic authorities, the Commonwealth Department of Infrastructure and Transport, the Australian Local Government Association, and NZ Transport Agency. Austroads is governed by a Board consisting of the chief executive officer (or an alternative senior executive officer) of each of its eleven member organisations:

Roads and Maritime Services New South Wales

Roads Corporation Victoria

Department of Transport and Main Roads Queensland

Main Roads Western Australia

Department of Planning, Transport and Infrastructure South Australia

Department of Infrastructure, Energy and Resources Tasmania

Department of Transport Northern Territory

Territory and Municipal Services Directorate Australian Capital Territory

Commonwealth Department of Infrastructure and Transport

Australian Local Government Association

New Zealand Transport Agency.

The success of Austroads is derived from the collaboration of member organisations and others in the road industry. It aims to be the Australasian leader in providing high quality information, advice and fostering research in the road transport sector.


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SUMMARY

This report presents the findings from the first year of a three year Austroads study which aims to maximise the re-use of reclaimed asphalt pavement (RAP) in new asphalt product. The objective of this first year of study is to improve the methodology for the characterisation of RAP binders and the design of the binder blend in asphalt mixes containing RAP.

A literature survey found that the Australian approach to accounting for the increase in viscosity of the binder blend due to the use of RAP is broadly in line with international best practice. This is true both on a national level in terms of the methodology proposed in the Austroads Asphalt Recycling guidelines AP-T66-06 (Austroads 2006), and on a state level in terms of the requirements set by road agencies for the use of different proportions of RAP in mixes. Characterisation of the properties of the blend of RAP and virgin binder is currently not part of standard practice in Australia. In some cases, the viscosity of the blend is corrected by adding a softer binder, but typically without checking the viscosity of the final product. Internationally, the characterisation of the properties of the extracted RAP binder, and design of an appropriate blend of RAP and virgin binder is often required, even at relatively low percentages of RAP in the final mix. It was also found that limited use was made of the binder viscosity prediction model in AP-T66-06 and the requirements for binder blends set in that document.

The experimental work showed that the dynamic shear rheometer (DSR) can be used for viscosity measurement as an alternative to both the Shell sliding plate test (viscosity at 45 °C) and the capillary viscosity test (viscosity at 60 °C). Although the DSR results for viscosity at 45 °C tend to be lower than those obtained using the Shell sliding plate, the DSR results are more repeatable than those of the Shell sliding plate test, which has conventionally been a common test used in Australia for the characterisation of RAP binder.

The results show that for the RAP sources under study, a blend of C170 with 10% to 20% RAP binder does result in a viscosity equivalent to that of a C320, as sometimes assumed in current practice.

The DSR based methodology used in this study provides a practical, consistent and cost-effective method to characterise RAP binder blends. As successfully demonstrated in this study, the viscosity results from the DSR tests can be used to design RAP binder blends to a desired viscosity. The methodology will be further validated during the next year of this study, when it will be used to design binder blends for asphalt mixes containing various percentages of RAP.


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CONTENTS

1 INTRODUCTION ................................................................................................................... 1 1.1 Arguments for the Re-use of RAP .......................................................................................... 1 1.2 Performance of High RAP Content Mixes .............................................................................. 1 1.3 Usage of Available RAP Stockpiles ........................................................................................ 2 1.4 Problem Statement ................................................................................................................ 3 1.5 Objectives .............................................................................................................................. 3 1.6 Structure of the Report ........................................................................................................... 3

2 STATE OF PARCTICE IN RAP BINDER CHARACTERISATION ......................................... 4 2.1 Interaction between RAP Binder and Virgin Binder ................................................................ 4 2.2 Properties of the RAP/Virgin Binder Blend ............................................................................. 5

2.2.1 State of Practice in Australia ....................................................................................... 5 2.2.2 Australian and New Zealand Road Agency Specifications with Regard to the

use of RAP ................................................................................................................. 7 2.2.3 RAP Binder Classification in the USA Prior to Superpave........................................... 8 2.2.4 Superpave Binder Classification for RAP .................................................................... 9 2.2.5 European RAP Mix Binder Classification .................................................................. 11

2.3 Discussion on State of Practice ........................................................................................... 12

3 EXPERIMENTAL WORK..................................................................................................... 14 3.1 Year 1: Characterising the Binder Blend .............................................................................. 14 3.2 Year 2: RAP Mix Performance ............................................................................................. 17 3.3 Year 3: High Performance High RAP Content Mix Design ................................................... 17 3.4 Laboratory Procedures ........................................................................................................ 18

3.4.1 Capillary Viscosity .................................................................................................... 18 3.4.2 Binder Extraction ...................................................................................................... 18 3.4.3 Production of the RAP Binder Blend ......................................................................... 18 3.4.4 DSR Creep Test ....................................................................................................... 18 3.4.5 DSR Frequency Sweep ............................................................................................ 18

4 RESULTS ............................................................................................................................ 21 4.1 ‘Conventional’ Viscosity Tests .............................................................................................. 21 4.2 Complex Viscosity Master Curves ........................................................................................ 21 4.3 Comparison between DSR and Shell Sliding Plate Results .................................................. 25 4.4 Viscosity at 60 °C ................................................................................................................. 28 4.5 Discussion of Results ........................................................................................................... 33

5 BLEND VISCOSITY PREDICTION ...................................................................................... 34 5.1 Comparing Viscosity Prediction Rules ................................................................................. 34 5.2 Designing Blends to a Desired Viscosity .............................................................................. 37

6 CONCLUSIONS AND PROPOSED BLEND SPECIFICATION GUIDELINE ....................... 39 6.1 Conclusions ......................................................................................................................... 39 6.2 Guideline for RAP Binder Blend Design and Specification ................................................... 40

REFERENCES ............................................................................................................................. 41


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TABLES Table 2.1: Typical requirements for rejuvenated binder ............................................................... 6 Table 2.2: Binder selection guidelines for RAP mixtures ........................................................... 10 Table 3.1: Initial test matrix binder blend tests per RAP source ................................................. 15 Table 3.2: Final test matrix binder blend tests per RAP source ................................................. 16 Table 3.3: Test matrix performance tests on RAP mixes ........................................................... 17 Table 4.1: Shell sliding plate and capillary viscosity results ....................................................... 21 Table 4.2: Summary of viscosity at 60 °C results from the capillary viscometer and

DSR at 1 rad/s .......................................................................................................... 30 Table 5.1: Complex viscosity at 60 °C, 1 rad/s for design blends .............................................. 38

FIGURES Figure 2.1: Example viscosity blending chart ................................................................................ 9 Figure 2.2: Example PG grade blending chart ............................................................................ 10 Figure 2.3: Comparison between Equation 1 and ASTM D4887 ................................................. 13 Figure 3.1: G* frequency/temperature sweep and master curve ................................................. 19 Figure 3.2: Relationship between G* and η* ............................................................................... 20 Figure 4.1: Master curves at 45 °C reference temperature for RAP1 – C170 blends .................. 22 Figure 4.2: Master curves at 45 °C reference temperature for RAP2 – C170 blends .................. 22 Figure 4.3: Master curves at 45 °C reference temperature for RAP1 – C320 blends .................. 23 Figure 4.4: Master curves at 45 °C reference temperature for RAP2 – C320 blends .................. 23 Figure 4.5: Master curves at 45 °C reference temperature for RAP1 – low viscosity oil

blends....................................................................................................................... 24 Figure 4.6: Master curves at 45 °C reference temperature for RAP2 – low viscosity oil

blends....................................................................................................................... 24 Figure 4.7: Viscosity at 45 °C for C170 – RAP1 blends .............................................................. 25 Figure 4.8: Viscosity at 45 °C for C170 – RAP2 blends .............................................................. 26 Figure 4.9: Viscosity at 45 °C for C320 – RAP1 blends .............................................................. 26 Figure 4.10: Viscosity at 45 °C for C320 – RAP2 blends .............................................................. 27 Figure 4.11: Viscosity at 45 °C low viscosity oil – RAP1 blends ................................................... 27 Figure 4.12: Viscosity at 45 °C low viscosity oil – RAP2 blends ................................................... 28 Figure 4.13: Comparison of viscosity readings from the DSR and capillary viscometer ................ 29 Figure 4.14: Shear rate data from historic capillary viscosity tests ............................................... 29 Figure 4.15: Viscosity at 60 °C for C170 – RAP1 blends .............................................................. 30 Figure 4.16: Viscosity at 60 °C for C170 – RAP2 blends .............................................................. 31 Figure 4.17: Viscosity at 60 °C for C320 – RAP1 blends .............................................................. 31 Figure 4.18: Viscosity at 60 °C for C320 – RAP2 blends .............................................................. 32 Figure 4.19: Viscosity at 60 °C for low viscosity oil – RAP1 blends .............................................. 32 Figure 4.20: Viscosity at 60 °C for low viscosity oil – RAP2 blends .............................................. 33 Figure 5.1: Fit of different models for a) viscosity at 45 °C for C170 and RAP1,

b) viscosity at 45 °C for C170 and RAP2, c) viscosity at 60 °C for C170 and RAP1, d) viscosity at 60 °C for C170 and RAP2 ................................................ 35

Figure 5.2: Fit of different models for a) viscosity at 45 °C for C320 and RAP1, b) viscosity at 45 °C for C320 and RAP2, c) viscosity at 60 °C for C320 and RAP1, d) viscosity at 60 °C for C320 and RAP2 ................................................ 36

Figure 5.3: Fit of different models for a) viscosity at 45 °C for oil and RAP1, b) viscosity at 45 °C for oil and RAP2, c) viscosity at 60 °C for oil and RAP1, d) viscosity at 60 °C for oil and RAP2 ..................................................... 36


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1 INTRODUCTION The re-use of reclaimed asphalt pavement (RAP) material in the production of new asphalt products has become standard practice, both internationally and locally. In many countries, including Australia, RAP is by far the most recycled construction waste product.

Various definitions for the acronym RAP are in use; with the letter R representing either ‘Recycled’ or ‘Reclaimed’ and the letter P either ‘Pavement’, or ‘Product’. In this report the term reclaimed asphalt pavement is used in accordance with the Austroads Glossary of Terms (Austroads 2010). Apart from asphalt material milled from roads, RAP stockpiles may also contain relatively fresh wastage or rejected product from the asphalt production process.

It is also important to make a distinction between re-use and recycling of asphalt pavement materials. Re-use of RAP is defined in this study as the utilisation of the product in its original application, that is in asphalt mixes. Recycling is often used to cover a wider range of utilisations of RAP material, including for instance the use of RAP in unbound layers of the road structure.

The maximisation of the re-use of RAP is beneficial for economic and environmental reasons as described below. The inclusion of RAP in asphalt mixes does require attention during the mix design process to ensure satisfactory performance of the product. The purpose of this study is to provide guidance on the design and specification of RAP mixes.

1.1 Arguments for the Re-use of RAP The re-use of RAP is often promoted from a sustainability point of view. Possibly the best known definition of sustainable development was provided by the Brundtland Commission (WCED 1987):

Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

From a sustainability perspective, the re-use of RAP in its original form has to be preferred over its use in lesser value applications such as granular layers. The re-use of RAP reduces the depletion of scarce resources, i.e. virgin bitumen and high quality crushed aggregates.

Notwithstanding the sustainability benefits, the main driver of the relative success of the re-use of RAP is the economic benefit. Various studies have reported significant cost savings to road authorities through the use of RAP (Al-Qadi et al. 2007). Provided that it can be sourced locally, RAP, especially at low percentages, can be added to a mix without incurring substantial additional costs to the production process. Each tonne of RAP replaces a tonne of virgin material (aggregate and binder) and thus saves on costs. To get the full economic benefit out of available RAP resources, re-use is also preferred over recycling in lesser value applications. Recycling may be a more cost effective solution in some situations, especially rural areas where there is no local capability for re-use of RAP.

Apart from providing a ready source of pre-processed material, the re-use of RAP also leads to cost savings for construction projects through a reduction in disposal costs.

1.2 Performance of High RAP Content Mixes In many countries as well as in parts of the industry in Australia, the use of RAP at percentages up to 25% to 30% in asphalt base layers is now generally considered to be standard practice. The performance of mixes containing low proportions of RAP can be expected to be equivalent to mixes containing only virgin materials (FHWA 2011). There is still some uncertainty surrounding the performance of mixes with higher (> 30%) RAP contents however. Also, the use of RAP in asphalt surfacing layers is typically more restrictive than the use in base layers. Past studies


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indicate that at high RAP contents the rutting performance of mixes may improve compared to mixes containing virgin materials, but the durability and fatigue performance may be negatively affected (Al-Qadi et al. 2007, Oliver 2001). On the other hand, examples of successful implementation of mixes containing very high RAP contents have also been reported, both internationally and locally, e.g. by Arnold et al. (2012), and Rebbechi and Green (2005). Internationally, rejuvenator agents are typically added in high RAP content applications to negate problems with durability and fatigue performance. A recent study by Tran et al. (2012) on the influence of rejuvenator on the performance properties of HMA found that rejuvenator has the ability to improve the fatigue performance, without necessarily decreasing the resistance against permanent deformation or negatively affecting the durability. Australia has so far only seen limited application of rejuvenators in the design of RAP mixes.

The production of asphalt mixes with almost 100% reclaimed asphalt has been reported to be technically feasible. This does however, require specialised equipment and cannot be achieved in conventional asphalt plants (CROW 2011). The maximum percentage that can be re-used is dependent on the type of asphalt plant. In a single drum operation the maximum achievable percentage of RAP may be limited to 25% due to the capacity to heat and dry the RAP. Using a parallel drum to pre-heat the RAP increases the capacity to about 50% RAP for both drum mixers and batch plants. In some double barrel drum mix plants it is possible to include up to 70% reclaimed material (CROW 2011). Some batch plants are also capable of producing mixes including even higher percentages of RAP. A recent study by Arnold et al. (2012) reports the successful production of asphalt mixes containing up to 90% RAP in batch plants. The high RAP content was achieved by adding a low viscosity fluxing oil to the RAP and only adding some virgin aggregate to correct for the increase in binder content. A mix design was created that met the relevant performance criteria. Such high percentages are only possible when the source of the RAP is very consistent and well controlled. In normal operation, 50% RAP content is the practical limit at which the grading can still be controlled by making adjustments to the virgin aggregate feed.

1.3 Usage of Available RAP Stockpiles In some countries, including, Austria, Canada, Germany, Japan, the Netherlands and the USA, more than 75% of the available reclaimed asphalt materials is re-used in new asphalt product (EAPA 2010). In Australia, RAP has been used in new asphalt mixes since the late 1970s. By 1990 up to 36% of the annually available RAP material was being utilised, although less than 5% of new asphalt production contained any RAP (Bowering 1991). In 2006, it was estimated that less than half of the reclaimed asphalt was being re-used in asphalt mixes. The remaining half was either used in cold recycling, or used as granular base or subbase materials, with the remainder going to landfill (Austroads 2006). Unfortunately there is no more recent data available on the use of RAP in Australia. At this stage there is no central effort in the industry to keep track of RAP usage. An extensive survey would be required to obtain this information and such an exercise falls outside the scope of the current project.

From discussions with various stakeholders from industry in Australia it was established that there is believed to be a trend to increasingly re-use RAP in asphalt mixes rather than using it in lower value applications. Also there is a perceived trend towards using higher percentages of RAP in asphalt mixes. The limited availability of RAP in Australia was identified as a possible inhibiting factor in the further growth of RAP re-use.

At the end of the previous century, two surveys of the Australian asphalt industry were performed to map the use of RAP and identify barriers to the further growth of its use (Alderson 1995, Holtrop & Alderson 1995, Oliver & Alderson 2000).


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The main findings of the survey conducted in 2000 were:

Between 1995 and 2000, the level of experience with recycling of RAP had increased.

The knowledge in industry of RAP specifications had also increased.

In the opinion of the researchers, RAP was still an undervalued resource.

Where RAP was used, an average 12% RAP was added to mixes.

Fumes were indentified as the dominant occupational health and safety concern involved with the use of RAP.

A lack of reliable information on the performance of RAP was seen as the main impediment to the growth of its use in mixes. It was recognised that this information probably already existed, but needed to be disseminated better.

Another local study on the implementation of mixes with high RAP contents identified rigid material specifications as the main barrier to the use of higher RAP percentages in asphalt mixes as well as to the use of other non-standard materials (Rebbechi & Green 2005).

1.4 Problem Statement From an economic and sustainability perspective, there is a need to maximise the re-use of RAP in Australia. The use of high percentages of RAP in asphalt mixes does however require due consideration in the design process. Clear mix design and specification guidelines are needed to aid asphalt producers, engineers, and road agencies in implementing high RAP content mixes, without negatively affecting the performance of the material. There is a need to verify whether the design of RAP mixes in Australia is still in line with international best practice.

1.5 Objectives The overall goal of the study is to reduce the uncertainty surrounding the performance of asphalt mixes containing high RAP content.

A three-year study has been planned and different objectives are set for each year. The current report contains the findings of the first year of the study.

In the current year of the study, the aim is to improve the methodology for the characterisation of RAP binders and the design of the binder blend in asphalt mixes containing RAP. The study will include characterisation of blends at a range of RAP contents mixed with virgin bitumen and rejuvenator.

The second year of the study will focus on the performance of asphalt mixes containing different percentages of RAP. The design guidelines for mixes containing RAP will be updated based on the results of these experiments and a study of international best practice.

The objectives for the final year of study are only tentative at this stage. The envisaged objective will be to develop guidelines for the design of high performance mixes containing high percentages of RAP.

1.6 Structure of the Report This introductory section is followed by a discussion on the state of practice in the design of binder blends containing RAP and virgin binder in Section 2. The research methodology for the laboratory study is presented in Section 3. The results of the laboratory test program are discussed in Section 4. In Section 5 guidelines for the design of binder blends containing RAP are presented, and Section 6 contains the conclusions from this research.


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2 STATE OF PARCTICE IN RAP BINDER CHARACTERISATION

As mentioned in the introduction, the focus for this first year of the study is the characterisation and design of the binder blend. The bitumen used in asphalt mixes age hardens due to oxidation taking place during production at the plant, transport to site, placement and service in the field. In the re-use of RAP, the influence of the hard reclaimed asphalt binder on the viscosity of the overall binder blend in the new mix is typically countered by using low viscosity virgin bitumen or rejuvenators (CROW 2011).

This section starts with a discussion on the extent to which blending between the RAP binder and the virgin binder or rejuvenator may be expected to take place in production of the new mix. Following this, the different methodologies to predict the properties of the combined RAP and virgin binder blend used both internationally and locally are reviewed. Finally, the main findings from the literature survey are discussed.

2.1 Interaction between RAP Binder and Virgin Binder In design methods for asphalt mixes containing RAP it is often assumed that the aged RAP binder mixes with virgin binder or rejuvenator to create a new blend with properties from the combined binders (Al-Qadi et al. 2007). The theory is that during the heating process at the asphalt plant, the RAP binder liquidises and blends completely with the virgin binder added in the process.

The extent to which blending of the binders takes place during production, remains the subject of scientific debate. An extensive study under the US National Cooperative Highway Research Program (NCHRP), found that blending of the RAP binder and virgin bitumen occurs to a significant extent (McDaniel et al. 2000).There is however, other research that indicates that mixing virgin binder with the RAP results to some degree in a double coat of old and new binder (Mollenhauer & Gaspar 2012). This last phenomenon is known as the ‘black rock’ scenario. The combined RAP aggregate, coated with the RAP binder, functions as solid aggregate when added to the mix. If the black rock scenario is proven to be accurate, this limits the cost savings achievable in the re-use of RAP, as the virgin binder content cannot be reduced on account of binder available in the RAP.

With respect to RAP binder blends, the Austroads framework for specifying asphalt (Austroads 2002) states:

Caution must be used in determining targets for blending of binders as fresh binder or rejuvenator may not be fully combined with the aged binder during the asphalt manufacture process. Consequently, mix performance characteristics imparted by binder stiffness, particularly fatigue and rutting resistance, may be somewhat intermediate between that of the fresh binder and that predicted from the stiffness or viscosity calculated or determined by extraction and testing of the blended binder.

Apart from the extent to which blending takes place, it has also been shown to take a certain amount of time for the blend to stabilise. As a result, the properties of the asphalt mix may change over time due to the binder blend becoming softer. Carpenter and Wolosick (1980) describe the interaction between the RAP binder as follows: First, the rejuvenator forms a very low viscosity layer surrounding the coated RAP aggregate. Then, rejuvenator starts to penetrate into the aged binder layer, decreasing the amount of free rejuvenator surrounding the aggregate and softening the aged binder. When no free rejuvenator remains, the penetration of the rejuvenator still continues, decreasing the viscosity of the inner layer and gradually increasing the viscosity of the outer layer. Finally, equilibrium is approached and the blend stabilises.


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During this process, the resistance against permanent deformation and stiffness of the mix decreases from when the material is first placed until the binder blend stabilises. The fatigue resistance of the mix on the other hand increases during this process. These effects need to be taken into account while assessing test results during the mix design phase (Carpenter & Wolosick 1980).This process is opposite to what is observed for conventional asphalt mixes, in which the permanent deformation is lowest when the mix is first placed and increases as the binder ages. The fatigue resistance for mixes without RAP reduces as the binder hardens. Carpenter and Wolosick (1980) further found the duration of the diffusion process to depend on the type of binders used. In contrast to the process described by Carpenter and Wolosick (1980), Oliver (2001) reported that for a mix containing 50% (artificially aged) RAP material the modulus, and rutting performance were lower than that of an equivalent mix containing only virgin materials. The explanation offered for this phenomen is that the rejuvenator did not immediately fully blend with the RAP binder, resulting in regions of low viscosity in the binder. This effect was expected to be less of an issue at lower percentages of RAP. From the work by Oliver (2001) and Carpenter and Wolosick (1980) it may be concluded that mix designers need to take into account that mixes containing RAP may not initially behave like mixes containing only virgin materials due to the time required for the diffusion process to complete.

In many cases the binder blend will consist of at least three different fractions, e.g. the RAP binder, the virgin bitumen and an additive or rejuvenating agent. Polymer modified blends for example, can be created by over-modifying the virgin binder before adding it to the mix containing RAP, in order to produce a blend at the proper modification level (Arnold et al. 2012). The influence of the final stable binder blend on the performance of the mix may be difficult to predict from binder testing only.

2.2 Properties of the RAP/Virgin Binder Blend In international practice, the influence of the RAP binder on the mix performance is typically assessed based on the percentage of RAP in the fresh mix. At low proportions of RAP in the asphalt mix, the influence of the hard RAP binder on the overall performance is typically ignored. At intermediate proportions of RAP, the overall viscosity of the blend is often corrected by using a relatively low viscosity virgin binder. At higher percentages of RAP, the properties of the binder blend are assessed in laboratory experiments.

2.2.1 State of Practice in Australia The National Asphalt Specification document released by AAPA (2004), proposes three levels of RAP use, i.e. 0–15%, 15–30%, and greater than 30%. For the lowest tier it is assumed that the influence of the RAP on the binder performance is negliglible and no special requirements are set. For mix designs containing between 15% and 30% RAP, the recommendation in the guideline is to use a softer bitumen grade to create a mix design that meets the design requirements. Finally, the specification document states that the use of mixes with more than 30% RAP should only be allowed if the contractor can show that suitable specialised plant technology is available to ensure that the RAP and virgin binder are not overheated in the process. It is recommended that at these high RAP contents, a suitable binder blend is designed that fullfills requirements comparable to what would be set for conventional bitumen. The specification framework for the design of mixes containing RAP was incorporated unaltered in Part 4B: Asphalt of the Austroads Guide to Pavement Technology (Austroads 2007).


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Actual binder requirements are not set in the AAPA specification framework, but the Austroads report AP-T66/06 Asphalt Recycling (Austroads 2006) does contain typical criteria for blends of RAP binders and virgin bitumen or rejuvenators. The criteria are shown in Table 2.1. The viscosity at 45 °C is measured using the sliding plate micro viscometer. An earlier version of the recycling guide included a maximum sliding plate viscosity requirement at 25 °C as well. A binder complying with the specifications shown in Table 2.1 would be similar to a Class 320 after rolling thin film oven (RTFO) treatment.

Table 2.1: Typical requirements for rejuvenated binder

Property Requirement

Min Max

Penetration at 25 °C 35 d mm -

Viscosity at 60 °C 350 Pa.s 900 Pa.s

Viscosity at 45 °C (heavy traffic) - 4.5 log Pa.s

Viscosity at 45 °C (light traffic) - 4.2 log Pa.s

Softening point 52 °C 56 °C Source: Austroads (2006). To design a blend of binders that combined have the desired viscosity, a viscosity prediction equation is provided in the Austroads Asphalt Recycling Guide. The proportions of RAP binder and rejuvenating agent, or virgin binder, required to create a binder that complies with the requirements in the table, are calculated using Equation 1. In an e-mail (personal communication dated 2 May 2013) to the main author of this report, Mr John Cunningham (NSW Roads and Maritime Services) described the origin of this equation. It can be traced back to work by Epps et al. (1980). In the original equation the viscosity was expressed in centipoise. A value of 3 was added to each term to convert from centipoise to pascal-seconds.

𝑟 =

log(𝑉 + 3) − log (𝑇 + 3)log(𝑉 + 3) − log (𝑅 + 3)

1

where

𝑟 = the mass fraction of total binder in the mix that is rejuvenating agent or virgin bitumen

R, T, V = logarithms of viscosity (log Pa.s) at a single temperature that is usually either 45 °C, or 60 °C

R = logarithm of the viscosity of the rejuvenating agent or fresh binder

T = logarithm of the target viscosity of the final product

V = logarithm of viscosity of the bitumen extracted from the RAP

An erroneous version of Equation 1 appeared in the 1997 version of the Asphalt Recycling Guide, which was later replaced by the correct equation shown above (Oliver 2001, Oliver & Alderson 2000). Literature contains numerous examples of blend viscosity equations.


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It is unclear to what extent blending equations and the specifications in Table 2.1 have been adopted into design practice for RAP mixes in Australia. A report on the use of mixes with high proportions of RAP in Australia (VicRoads 2009) states:

In practice, the testing of recovered binder from manufactured asphalt was found to be troublesome. The cost of testing was significant and the results variable. Variability was never fully explained but it is speculated incomplete blending of old and new binder may have been a factor.

The costs involved with the testing shown in Table 2.1 will depend on the selected binder extraction process and test methods. Some binder extraction processes yield only small amounts of RAP binder at a time. To perform tests like the dynamic viscosity at 60 °C and the penetration test the yield of dozens of RAP binder extractions may required, which is laborious and costly.

In Australian practice it is typically assumed that the viscosity of the binder blend can be corrected by adding a softer class 170 bitumen to the mix, without performing laboratory tests on the binder blend. Local research by Rebbechi and Green (2005) has shown that RAP contents of up to 40% can be accommodated by using a softer C170 binder in mixes which yield performance equivalent to asphalt mixes with virgin C320 binder.

2.2.2 Australian and New Zealand Road Agency Specifications with Regard to the use of RAP

The various road agencies in Australia and New Zealand apply different specifications for the use of RAP and the correction of binder stiffness. The criteria published by each road agency are summarised below.

Depending on the mix type, VicRoads allows certain percentages of RAP to be added to asphalt mixes unconditionally, provided that the original mix design meets the relevant criteria for the mix type (VicRoads 2012). For Type L (light duty wearing course) mixes up to 20% of RAP may be added, for Type N (light duty wearing course) mixes, 15%, 10% for mix Type H (heavy duty wearing course), up to 20% for mix types SI and SG (multi purpose base course) mixes and up to 30% for Type SF (fatigue resistant base course).

VicRoads requires a ‘soft’ Class 170 bitumen to be used if more than 10% RAP is added to Type L and N mixes.

The VicRoads Code of Practice for the registration of bituminous mix designs (VicRoads 2012) states that mixes including higher percentages of RAP may be permitted, provided that additional performance testing is carried out on the mix.

VicRoads does not permit the use of RAP in asphalt mixes which contain polymer modified binder.

The New South Wales Roads and Maritime Services (RMS) QA specification R116 (RMS 2012) allows the use of up to 15% RAP provided that the RAP source material meets certain basic criteria. The RAP content may be increased up to 25% for base courses and up to 20% for wearing courses provided that performance tests are conducted on the mix design, and proof of satisfactory field performance can be provided over a set period of time. The performance trial period is two years for base courses and three years for wearing courses. The RAP content for base courses may be further increased to 30% and 40%, provided that performance can be proven over a period of three and five years respectively. A further requirement for the 30% and 40% RAP levels is that the mix design is optimised using performance testing, rather than just validated. The RMS specification requires the viscosity of the RAP binder to be determined and reported.


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Main Roads Western Australia allows the use of up to 10% RAP in asphalt intermediate course layers, provided that the RAP material meets certain basic criteria (Main Roads Western Australia 2013).

The South Australia Department of Planning Transport and Infrastructure requires asphalt mixes containing RAP to meet the same design criteria used for mixes excluding RAP. For mixes containing up to 15% RAP, no correction for the increase in binder viscosity is required. For mixes containing 20% RAP, C170 bitumen shall be substituted for C320 bitumen. RAP proportions over 20% are not allowed (South Australia Department of Planning Transport and Infrastructure 2010).

The Queensland Department of Transport and Main Roads allows the addition of up to 15% RAP in dense graded base courses and heavy duty base courses. The use of RAP for wearing courses is not allowed (Department of Transport and Main Roads 2010, 2011).

The Department of Infrastructure, Energy and Resources of Tasmania, requires separate designs to be prepared for mixes containing RAP (Department of Infrastructure, Energy and Resources 2011). The inclusion of up to 15% RAP is allowed for general use, except where excluded from the Project Specification. The use of 15% to 30% RAP is allowed except in heavy and very heavy wearing course mixes, mixes containing polymer modified binder, or where excluded in the Project Specification. In the 15% to 30% RAP content category it is allowed to correct for the increased viscosity of the RAP binder by using a softer virgin binder. With respect to mixes containing more than 30% RAP, the R55 specification (Department of Infrastructure, Energy and Resources 2011) states that these shall only be accepted where the contractor can demonstrate suitable manufacturing plant and quality control procedures to ensure production of hot mix asphalt as specified.

New Zealand Transport Agency allows the use of up to 15% RAP in asphalt mixes. Mixes with higher contents of RAP may be approved at the discretion of the NZTA Engineering Policy Manager (New Zealand Transport Agency 2005).

The specifications of the Northern Territory Department of Construction and Infrastructure do not contain specific requirements for asphalt mixes containing RAP (Department of Construction and Infrastructure 2010).

2.2.3 RAP Binder Classification in the USA Prior to Superpave Prior to the introduction of the Superpave Performance Grade (PG) binder specification system, both a viscosity grade, and a penetration grade system were used in the USA. The Asphalt Institute published a methodology to create blends of RAP binder and virgin bitumen at a desired viscosity level, using blending charts (Asphalt Institute 1986). This methodology is also described in the US standard test method ASTM D4887-99. A hypothetical example of a blending chart is shown in Figure 2.1. The viscosity of the RAP binder, as determined from testing, is plotted on the left vertical axis, and the viscosity of the virgin bitumen, or recycling agent, on the right vertical axis. A linear relationship is assumed between the log of the viscosity in the blend and the weight ratio of the different binders. This approach is similar to the methodology proposed in the Austroads recycling guide, except that Equation 1 uses a double log scale instead of the single log form used in the ASTM relationship. The Asphalt Institute approach implies the log linear relationship between the viscosity of the different binders shown in Equation 2:

𝑎 log 𝜂1 + 𝑏 log 𝜂2 = (𝑎 + 𝑏) log 𝜂𝑚𝑖𝑥 2

where a and b are the ratios of the different binders in the blend and a + b = 1. η1 is the viscosity of binder 1, η2 is the viscosity of binder 2 and ηmix is the viscosity of the blend.


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Figure 2.1: Example viscosity blending chart

The Asphalt Institute viscosity blending charts with a linear relationship between the log viscosity of the different binders have been shown to provide reliable results for soft bitumen types. For blends including rejuvenator oils however, the viscosity prediction is less precise (Chaffin et al. 1995).

2.2.4 Superpave Binder Classification for RAP The viscosity grading system for binders in the USA was replaced in the 1990s with a Performance Grade (PG) system as part of the superior performing asphalt pavements (Superpave) design method. The PG binder selection system ranks a binder in terms of its performance at high and low temperatures. A PG 64-16 binder for instance is (within a defined range of loading conditions) deemed suitable for use in a pavement where the annual seven day maximum average temperature at a depth of 20 mm in the pavement is below 64 °C, and the annual average minimum surface temperature above –16 °C. The high temperature grade relates to rutting performance and is determined from dynamic shear rheometer (DSR) testing. The rutting parameter is determined for the virgin binder as well as for the binder after rolling thin film oven treatment (RTFOT) aging. The low temperature grade relates to fatigue and is determined from DSR testing on binder conditioned for long term aging using the pressure aging vessel (PAV), as well as bending beam rheometer (BBR) testing of this binder. An advantage of the PG system over earlier binder classification systems, is that it allows for modified binders to be classified using the same system.

The original Superpave asphalt mix design method developed under the US Strategic Highway Research Program (SHRP) by Kennedy et al. (1994), did not make specific provision for the inclusion of RAP. In subsequent work by the Federal Highway Administration (FHWA) Superpave Mixtures Expert Task Group a guideline was developed for the design of Superpave asphalt mixtures containing RAP (Bukowski 1997). This guideline divided mixtures into three categories depending on the percentage of RAP. For Tier 1, with up to 15% RAP no bitumen grade adjustment is made to compensate for the hard RAP binder. For Tier 2, covering mixes containing 16% to 25% RAP a Performance Grade (PG) binder is selected of one grade lower than required for both the low and high design temperatures. Instead of a PG 72-16, a PG 64-22 would be selected for example. Mixes with a RAP content higher than 25% were placed in Tier 3. For this tier it was suggested that the properties of the binder recovered from the RAP are characterised, and a suitable blend of RAP and virgin bitumen would be designed using a blending chart to obtain a binder of the required PG grade.


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The use of a tiered system was validated in an extensive NCHRP study on the suggested use of RAP in Superpave mixtures (McDaniel et al. 2000, 2001). Based on this study, the tier structure was altered to account for the extent to which the RAP binder has aged. Different tiers are provided depending on the low temperature PG grade of the recovered RAP. The new tier system is shown in Table 2.2. The use of this system does imply that, unless the RAP content is below 10%, the PG grade of the binder blend needs to be determined through laboratory testing.

Table 2.2: Binder selection guidelines for RAP mixtures

RAP percentage

Recovered RAP grade

Suggested virgin asphalt binder grade PG xx-22 or lower PG xx-16 PG xx-10 or higher

No change in binder selection < 20% < 15% < 10%

Select virgin binder one grade softer than normal (e.g. select a PG 58-28 if a PG 64-22 would normally be used)

20–30% 15–25% 10–15%

Follow recommendations from blending charts > 30% > 25% > 15% Source: After McDaniel et al. (2001). The procedure to develop blending charts for RAP and virgin binder is described by McDaniel and Anderson (2001). The RAP blending chart procedure requires both the virgin binder and the binder recovered from the RAP to be characterised according to the PG system. The PG of both binders is plotted on either side of the blending chart, a hypothetical example of which is shown in Figure 2.2. A linear relationship is assumed between the proportion of the binders in the blend and the combined PG grade, allowing the selection of the RAP content that will yield the desired combined PG.

Figure 2.2: Example PG grade blending chart


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The existence of a linear relationship between the binder proportions and the combined PG is not universally supported by research. Kennedy et al. (1998) performed a study of the influence of the percentage of RAP binder on the properties of the bitumen blend. Superpave binder performance indicators for stiffness, rutting and fatigue were obtained for binder blends with different percentages of RAP and virgin binder. The study found that a linear relationship between the rate of stiffness increase and the proportion of RAP binder does not exist in all cases. The study recommended that since the characteristics of individual virgin and reclaimed binders differ, the properties of each blend should be assessed individually.

2.2.5 European RAP Mix Binder Classification According to the European material specification for reclaimed asphalt EN 13108-8:2008, the RAP penetration value of the binder may be declared a grade P15 bitumen, provided that the mean of the penetration measurements is at least 15 d mm and that each measured penetration value is at least 10 d mm. Alternatively, the RAP binder may be classified a S70 bitumen, provided that the mean softening point is below 70 °C and all softening point measurements are below 77 °C. In other cases the mean penetration value or mean softening point value shall be used to classify the RAP bitumen.

According to the European specifications for asphalt mixes in EN 13108-1:2008, the binder class of the virgin binder may be used unaltered if the mix design includes less than 10% RAP for surfacing layers and less than 20% RAP for base layers and binder courses. If higher proportions of RAP are used, the penetration and softening point values of the binder blend are to be determined using the equations in EN 13108-1 Annex A, shown here as Equation 3 and Equation 4 respectively. The calculated penetration and softening point have to satisfy the relevant criteria set for the mix design.

𝑎 log𝑝𝑒𝑛1 + 𝑏 log𝑝𝑒𝑛2 = (𝑎 + 𝑏) log𝑝𝑒𝑛𝑚𝑖𝑥 3

where

𝑝𝑒𝑛1 = the penetration of the binder recovered from the RAP

𝑝𝑒𝑛2 = the penetration of the added virgin binder

𝑝𝑒𝑛𝑚𝑖𝑥 = the calculated penetration value of the binder in the mixture containing RAP

𝑎, 𝑏 = ratios by mass of the binder from the RAP and of the virgin binder respectively (𝑎 + 𝑏 = 1.0)

𝑇𝑅&𝐵 𝑚𝑖𝑥 = 𝑎 𝑇𝑅&𝐵 1 + 𝑏 𝑇𝑅&𝐵 2 4

where

𝑇𝑅&𝐵 𝑚𝑖𝑥 = the softening point of the binder in the mixture containing RAP

𝑇𝑅&𝐵 1 = the softening point of the binder recovered from the RAP

𝑇𝑅&𝐵 2 = the softening point of the added virgin binder

𝑎, 𝑏 = ratios by mass of the binder from the RAP and of the virgin binder respectively (𝑎 + 𝑏 = 1.0)


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The harder the RAP binder, the less likely effective blending of the RAP and virgin binder becomes. Therefore, European countries have set limit values to the the hardness of the RAP binder in terms of penetration and softening point. An overview of the requirements in various European countries is provided by Ipavec et al. (2012).

Although specifications in Europe are still based on the empirical softening point and penetration test, the DSR is also increasingly used to characterise binders. Recently, in a study of particular relevance to this Austroads project, Mangiafico et al. (2012) used the DSR to characterise various blends of RAP with virgin binder. The characteristics of the binder blends were then compared to the performance of asphalt mixes produced with these blends.

2.3 Discussion on State of Practice From the literature review it appears that the Australian approach to accounting for the increase in viscosity of the binder blend due to the use of RAP is broadly in line with international best practice. This is true both on a national level in terms of the methodology proposed in the Austroads Asphalt Recycling guidelines AP-T66/06 (Austroads 2006), and on a state level in terms of the requirements set by road agencies for the use of different proportions of RAP in mixes.

Currently however, it is not practice in Australia to verify the properties of the blend of RAP and virgin binder. Either RAP is added without correcting for the change in viscosity of the binder, or it is assumed that the the viscosity increase of the binder in RAP mixes can be corrected by adding a softer binder class without necessarily determining the properties of the actual binder blend. In both the European Union and the USA, the characterisation of the properties of the extracted RAP binder, and design of an appropriate blend of RAP and virgin binder is often required, even at relatively low percentages of RAP in the final mix.

It appears that, in Australian practice, limited use is made of the binder viscosity prediction model in Equation 1 to create binder blends with suitable properties at high proportions of RAP. This may be due to a combination of factors, including the high costs involved with performing the required tests on extracted RAP binder. The uncertainty regarding reliability of such prediction models is another factor. There is still scientific debate around the extent to which RAP binder and virgin binder mix during asphalt production.

The form of the viscosity relationship in Equation 1 differs from the log linear relationship between the rate of stiffness increase and the proportion of reclaimed binder assumed in the viscosity blending sheets approach developed by the Asphalt Institute and described in ASTM D4887. As mentioned earlier, ASTM D4887 is known to be accurate for soft bitumen, but has limited applicability for blends containing low viscosity rejuvenators. This may be the reason for the different form of Equation 1 used in the Austroads guideline. To investigate the influence of the shape of the relationship on the accuracy of the prediction, both approaches were applied to a set of published data. Carey and Paul (1980) performed viscosity tests on a range of blends containing different percentages of aged binder and rejuvenator. The experimental matrix included several bitumen and rejuvenator types. The results for a set of data are shown in Figure 2.3. Equation 1 offers an improved fit to the data compared to the ASTM D4887 approach.

Based on the literature review it is concluded that there is a need to investigate the validity and the practicality of the specifications for binder blends in AP-T66/06 (Austroads 2006).

Also, the limits of the common practice of correcting for the increased viscosity of the binder in RAP mixes by adding a softer binder class, without experimentally determining the characteristics of the binder blend, needs to be investigated.


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Figure 2.3: Comparison between Equation 1 and ASTM D4887


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3 EXPERIMENTAL WORK The laboratory component of this study is planned to span three years. The objective in this first year (2012–13) is to validate and improve the existing guidelines for the characterisation and design of the binder blend in RAP mixes. The study includes characterisation of blends at a range of RAP contents mixed with virgin bitumen and a suitable rejuvenator oil.

The second year of the study (2013–14) will focus on the performance of mixes containing different percentages of RAP. The aim is to improve the design guidelines for mixes containing RAP based on the laboratory results and a review of international best practice.

The objectives of the experiments for the final year of study (2014–15) have yet to be finalised. At this stage it is expected that the aim will be to develop high performance mixes at very high RAP content levels.

3.1 Year 1: Characterising the Binder Blend To fully validate the current requirements for the characterisation of RAP binder blends and Equation 1, it would be necessary to perform tests as shown in Table 2.1 for a range of blends. Such a test matrix was developed and is shown in Table 3.1. Binder recovered from RAP would be blended with fresh binder or rejuvenator at different proportions of RAP. The blends would then be tested for the parameters in Table 2.1, as well as using the DSR. The testing would also be performed after Rolling Thin Film Oven Treatment (RTFOT), to simulate the aging of the binder blend during production in an asphalt plant.

In developing the laboratory test plan, the issue of high costs involved with the testing on RAP blends raised in Section 2 quickly becomes apparent. A binder extraction in accordance with ARRB method M07 yields about two grams of RAP binder. Hence, many extractions are required to perform a dynamic viscosity test, which uses 80 grams, or to do a penetration test, which uses approximately 50 grams. Furthermore, the RTFOT procedure requires 35 grams, only 30% of which is recovered for testing. The costs of running the tests in Table 3.1 were estimated at almost double the total 3-year budget of the RAP research project, with binder extraction accounting for 87% of the costs. The costing showed the need for a significantly reduced scope of testing.


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Table 3.1: Initial test matrix binder blend tests per RAP source

Test RAP binder content (%) Total Blends 0 10 15 20 30 60 90

Recovered RAP binder AP-T66/06 tests 2 2 DSR temperature and frequency sweep 2 2 Recovered RAP binder after RTFOT AP-T66/06 tests 2 2 DSR temperature and frequency sweep 2 2 Class 320 AP-T66/06 tests 2 2 2 2 8 DSR temperature and frequency sweep 2 2 2 2 8 After RTFOT (on C320 and RAP) AP-T66/06 tests 2 2 2 2 8 DSR temperature and frequency sweep 2 2 2 2 8 Class 170 AP-T66/06 tests 2 2 2 2 8 DSR temperature and frequency sweep 2 2 2 2 8 After RTFOT (on C170 and RAP) AP-T66/06 tests 2 2 2 2 8 DSR temperature and frequency sweep 2 2 2 2 8 Low viscosity oil AP-T66/06 tests 2 2 2 6 DSR temperature and frequency sweep 2 2 2 2 8 After RTFOT (on oil and RAP) AP-T66/06 tests 2 2 2 6 DSR temperature and frequency sweep 2 2 2 2 8

In contrast to the dynamic viscosity, or penetration tests, DSR testing only requires a small amount of recovered binder (approximately one gram). Internationally, the DSR is being increasingly used as the standard piece of equipment to characterise bituminous binders. Also, the complex viscosity (η*) determined using the DSR can used to predict the dynamic viscosity and even the penetration value. To create a comprehensive test matrix within the available budget, it was decided to reduce the scope of testing, relying more on DSR testing and eliminating tests from Table 2.1 that required large quantities of extracted binder. The final laboratory test matrix is shown in Table 3.2, testing is limited to the binder blend in its original state, i.e. RTFOT was excluded. The aim was to develop a RAP binder blend characterisation method that is both reliable and cost effective.

The only test retained from Table 2.1 is the Shell sliding plate viscosity at 45 °C in accordance with AS 2341.5. This test only requires a small amount of binder. The results are used to further validate the known correlation between DSR testing and more conventional viscosity tests.

The DSR testing was conducted on a binder blend in two subsequent steps, as follows:

Step 1 – a creep test with varying stress levels at 45 °C

Step 2 – a temperature and frequency sweep test performed to develop η* master curves for the blend. Frequency sweeps were performed at 5 °C intervals within a temperature range from 65 °C to 25 °C and over a frequency range from 0.1 to 10 Hz.


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The η* master curve was used in this report to validate blending Equation 1. The dynamic viscosity at 60 °C for the blends was also estimated from the master curve. The relationship between the Shell sliding plate viscosity at 45 °C and the complex viscosity at 45 °C determined using the DSR is analysed further in Section 4.3. The DSR creep test results at 45 °C are also compared to Shell sliding plate results in that same section.

Table 3.2: Final test matrix binder blend tests per RAP source

Test RAP binder content (%) Total Blends 0 10 15 20 30 60 90

Recovered RAP binder Viscosity at 45 °C (AS 2341.5) 3 3 DSR sweep and creep test (AASHTO T315)** 2 2 Class 320 Viscosity at 45 °C (AS2341.5) 3 3 3 3 12 DSR sweep and creep test (AASHTO T315)** 2 2 2 2 8 Dynamic viscosity 60 °C (AS 2341.3) 2 2 Class 170 Viscosity at 45 °C (AS 2341.5) 3 3 3 3 12 DSR sweep and creep test (AASHTO T315)** 2 2 2 2 8 Dynamic viscosity 60 °C (AS 2341.3) 2 2 Low viscosity oil Viscosity at 45 °C (AS 2341.5) 3 3 3 9 DSR sweep and creep test (AASHTO T315)** 2 2 2 2 8 Dynamic viscosity 60 °C (AS 2341.3) 2 2 Design blend DSR sweep and creep test (AASHTO T315)** 2*

* Percentage RAP to be determined. ** There is no standard test procedure for DSR in Australia, tests were performed in accordance with AASHTO T315-10 (AASHTO 2009).

The test matrix in Table 3.2 was completed for RAP from two different sources. RAP samples were sourced from Western Australia, as well as from a local asphalt plant in the Melbourne area.

The percentages of RAP binder and the types of virgin binder and rejuvenator in Table 3.2 were selected based on the currently suggested tiers of RAP use. The tests provided viscosity data on the following:

the RAP binder

each virgin binder or rejuvenator

the Class 320 binder blended with 0–20% of RAP binder

the Class 170 binder blended with 0–30% of RAP binder

the low viscosity oil (rejuvenator) blended with 30–90% of RAP.

The results are used to validate the viscosity prediction equations and also to provide more insight into the viscosity of the binder blend at RAP percentages currently suggested in Australia.

The final row of Table 3.2 shows testing on a designed blend. The aim of this last task is to design a blend of virgin binder, a high percentage of RAP and a rejuvenator to meet the criteria for a Class 320 bitumen. It basically is a validation exercise, to investigate whether the models evaluated in this study can be used to create a binder blend conforming to predetermined specifications.


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3.2 Year 2: RAP Mix Performance The tentative test plan for year two is shown in Table 3.3. The aim of the testing is to characterise the performance of asphalt mixes containing RAP. Tests will be performed using an existing dense graded standard mix design with Class 320 binder. Different percentages of RAP will be added, while keeping the aggregate grading unchanged. One of the objectives of the study is to investigate whether the use of a softer virgin bitumen can correct the performance of the mix for the increased viscosity of the RAP binder, as assumed in AP-T66/06 Asphalt Recycling. Finally, the viscosity prediction equation, developed in year one of the study, will be used to design a binder blend at high RAP contents (30%, 60% and 90%). The aim will be to create binders with a viscosity equivalent to a Class 320 binder and then compare the performance of these mixes to that of the original mix design without RAP. The experimental plan may be adjusted based on the outcomes of a survey exploring concerns around the use of RAP among Asphalt Research Working Group members to be conducted at the start of year two.

Table 3.3: Test matrix performance tests on RAP mixes

Test RAP content (%) Total

0 15 30 60 90 Mix with Class 320 binder Gyratory volumetrics 2 2 4 Maximum density 2 2 4 Modulus 2 2 4 Wheel tracking 2 2 4 Fatigue 9 9 18 Moisture sensitivity 2 2 4 Mix with Class 170 binder Gyratory volumetrics 2 2 4 Maximum density 2 2 4 Modulus 2 2 4 Wheel tracking 2 2 4 Fatigue 9 9 18 Moisture sensitivity 2 2 4 Mix with designed binder blend Gyratory volumetrics 2 2 2 6 Maximum density 2 2 2 6 Modulus 2 2 2 6 Wheel tracking 2 2 2 6 Fatigue 9 9 9 27 Moisture sensitivity 2 2 2 6

3.3 Year 3: High Performance High RAP Content Mix Design The test plan for year three will be finalised based on the outcomes for year two. The goal will be to develop high performance RAP mixes. Optimum use will be made of the characteristics of the RAP binder to create mixes that can perform in heavy traffic situations.


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3.4 Laboratory Procedures In this section, the laboratory procedures utilised to characterise binder blends containing RAP during this first year of study are discussed.

3.4.1 Capillary Viscosity Capillary viscosity tests at 60 °C were performed on the virgin binder samples in accordance with AS 2341.2-1993.

3.4.2 Binder Extraction Binders were extracted in accordance with ARRB method M07 (ARRB 2005), available from the ARRB library. The objective of the method is to provide a sample of the binder representative of its in-service condition primarily in terms of measured viscosity. To achieve this, the sample was soaked in toluene in a flask at room temperature and the bituminous binder dissolved in toluene was decanted out. After centrifuging the toluene liquid was evaporated in an RTFO oven at 100 °C under carbon dioxide to prevent oxidation. The binder was recovered from the RTFO bottles using a razor. This test has been evaluated extensively in past local research and it has been shown that representative binder samples can be obtained.

3.4.3 Production of the RAP Binder Blend Mixes of various percentage RAP and base binder were produced in accordance with the proportions in Table 3.3. The mass required for each mix/blend was calculated and checked. After this, the samples were heated until fluid, stirred and quantities were weighed and recorded. Each mix was heated for a minimal time under a heat lamp and stirred vigorously with a spatula until homogenised. All sub-samples to be tested were weighed/created at the same time, so each individual mix was only heated once further, re-stirred with a spatula and then tested.

3.4.4 DSR Creep Test Duplicate DSR tests were carried out in creep mode at 45 °C on all base binders and RAP blends. An initial stress sweep test was carried out at a shear rate of 0.005 s-1 to identify appropriate stress levels. The creep test was then performed at the pre-determined stress levels for a given time (three minutes). The data was then plotted and used to find the viscosity at the required shear rate of 0.005 s-1. The DSR creep test was developed to replicate the results from the Shell sliding plate test, as described in detail in report AP-T225-13 (Austroads 2013). Earlier local work on comparisons between the Shell sliding plate test and the DSR in the field of durability was performed by Halligan and Chatard (2010).

3.4.5 DSR Frequency Sweep Duplicate DSR temperature frequency sweep tests in oscillation mode were carried out immediately after the creep test of all base binders and RAP blends. The DSR test was carried out under oscillation frequencies (f) of 0.1–10 Hz at 5 °C temperature intervals between 25 °C and 65 °C.

DSR results are often presented using angular velocity (ω) rather than oscillation frequency (f). The relation between ω and f is provided in Equation 5.

𝜔 = 2𝜋𝑓 5

where 𝜔 = angular frequency (rad/s) 𝑓 = the ordinary frequency, the number of oscillations per second (Hz)


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The DSR equipment records the shear stress required to rotate the spindle as well as the time lag between the maximum rotation and the maximum shear stress. The material parameters of primary importance for the current study determined from this data are the complex viscosity (η*), the complex shear modulus (G*) and the phase angle (δ). Figure 3.1 shows the G* results for a temperature and frequency sweep test. The results at individual temperatures are shifted to form one continuous master curve also shown in the figure. The shift is performed by fitting the various curves to a sigmoidal model using regression analysis, the fitting process is described later. This sigmoidal model is frequently used to construct complex modulus master curves for both bituminous binders and asphalt mixtures. Using the sigmoidal model master curve the data range can be extrapolated in order to estimate the G* or η* at any combination of temperature and load frequency. The master curve in the figure is developed at a set reference temperature of 45 °C. Viscosities at relevant load frequencies and temperatures of 25 °C, 45 °C and 60 °C were calculated from the master curve to estimate the results from the penetration test at 25 °C, Shell sliding plate at 45 °C and the dynamic capillary viscometer at 60 °C.

Figure 3.1: G* frequency/temperature sweep and master curve

The sigmoidal function fitted to the G* results in Figure 3.1 is shown as Equation 6. This model is widely used in asphalt technology, including in the USA mechanistic empirical pavement design guide (MEPDG) (NCHRP 2004).

𝑙𝑜𝑔|𝐺∗| = 𝛿 +𝛼

1 + 𝑒𝛽+𝛾{log𝑓𝑟} 6

where

𝑓𝑟 = reduced frequency (rad/s)

𝛼,𝛽, 𝛾, 𝛿 = fitting parameters


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The results of the dynamic modulus tests are shifted with respect to time of loading until a single smooth curve emerges, by means of the reduced frequency parameter (fr). The reduced frequency is defined as the actual loading frequency multiplied by the time-temperature shift factor, a(T) as shown in Equation 7.

𝑓𝑟 = 𝑎(𝑇) × 𝑓 7

where

𝑓 = frequency (rad/s)

𝑎(𝑇) = shift factor as a function of temperature (°C)

𝑇 = temperature (°C)

The temperature shift factor is calculated from Equation 8. Microsoft Excel solver can be used to simultaneously determine the optimum values for the fitting parameters for Equation 6 and Equation 8, by maximising the coefficient of determination (R2) of the fit.

𝐿𝑜𝑔 𝑎(𝑇) = 𝑎𝑇2 + 𝑏𝑇 + 𝑐 8

where

ɑ, b, c = fitting parameters

The η* master curve can be obtained from the G* master curve using η*= G*/ft as shown in Figure 3.2.

Figure 3.2: Relationship between G* and η*


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4 RESULTS In this section the results of various viscosity tests on the binders and binder blends are presented. The results of the conventional viscosity tests are presented first, followed by the results obtained from the DSR. From this, relationships between the DSR results and conventional tests are assessed. Finally, the significance of the different findings is summarised in a discussion section.

4.1 ‘Conventional’ Viscosity Tests The mean results for the Shell sliding plate tests at 45 °C and capillary viscosity at 60 °C for the individual binders tested as part of this project are shown in Table 4.1. The results indicate that the dynamic viscosity at 60 °C for the Class 170 and Class 320 bitumen falls within the respective specification limits. The Shell sliding plate results show the marked difference in viscosity between the virgin binders and the RAP binders. The sliding plate results also show an order of magnitude difference in the viscosity at 45 °C between RAP1 and RAP2. Due to its low viscosity at these temperatures, low viscosity oil could not be tested using these conventional test methods. No capillary viscosity tests were performed on the extracted RAP binders because of the large amount of binder required for this test.

Table 4.1: Shell sliding plate and capillary viscosity results

Binder Mean viscosity results (Pa.s)

Shell sliding plate 45 °C Capillary viscosity 60 °C C170 2316 178 C320 3819 305 Low viscosity oil No result No result RAP1 248638 Not tested RAP2 2852113 Not tested

4.2 Complex Viscosity Master Curves Figure 4.2 to Figure 4.6 show the η* master curves from DSR tests on samples of the three virgin binders at various percentages of RAP1 or RAP2. The master curves were developed based on the average of the G* results for duplicate tests. The graphs show the increase in viscosity with the increase in RAP content. For the same RAP content, blends containing RAP2 have a significantly higher viscosity than blends containing RAP1, due to the higher viscosity of the RAP2 binder.


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Figure 4.1: Master curves at 45 °C reference temperature for RAP1 – C170 blends



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Figure 4.5: Master curves at 45 °C reference temperature for RAP1 – low viscosity oil blends

Figure 4.6: Master curves at 45 °C reference temperature for RAP2 – low viscosity oil blends


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— 25 —

4.3 Comparison between DSR and Shell Sliding Plate Results The Shell sliding plate test is often used in Australia to characterise RAP blends. In this section, the viscosity values obtained with the DSR are compared to the sliding plate results to assess whether equivalent results may be obtained from both test methods. The intention is to evaluate the DSR as an alternative to the sliding plate test in future specifications of binder blends containing RAP. Figure 4.7 to Figure 4.10 show the viscosity results at 45 °C for the Class 170 and Class 320 binders blended with various percentages of RAP. A simple exponential function was fitted to the results to indicate the trend of increasing viscosity with increasing proportion of RAP in the measurements. Plotted in the graphs are the results from both the Shell sliding plate test, as well as from the DSR creep test and from the DSR frequency sweep test, both at a shear rate of 0.005 s-1. The results indicate that the DSR frequency sweep test can be used to obtain a test parameter equivalent to the viscosity measured in the DSR creep test. At the selected load rate, both DSR tests yield a lower viscosity value at 45 °C than the Shell sliding plate test. The DSR tests however are more repeatable (show less scatter) and therefore have a higher precision than the Shell sliding plate test.

The results for the blends of low viscosity oil with RAP are shown in Figure 4.11 and Figure 4.12. The Shell sliding plate method was not able to produce valid measurements for the 100% low viscosity oil sample and the blends containing the oil and 30% or 60% RAP due to their low viscosity, therefore those results are not reported. It was also not possible to obtain results using the DSR tests at the low shear rate; therefore the shear rate was increased to 1 s-1 at which setting valid viscosity results were obtained. The results indicate that the simple exponential trend line used in the graph does not suitably describe the shape of the trend in the viscosity of the blends containing low viscosity oil. Other more suitable models will be fitted in the Section 5.

Figure 4.7: Viscosity at 45 °C for C170 – RAP1 blends

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osity

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DSR T/F sweepDSR CreepShell sliding plateDSR T/F sweep log-linear predictionDSR creep log-linear predictionShell sliding plate log-linear prediction


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osity

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DSR T/F sweepDSR creepShell sliding plateDSR T/F sweep log-linear predictionDSR creep log-linear predictionShell sliding plate log-linear prediciton

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osity

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DSR T/F sweepDSR CreepShell sliding plateDSR T/F sweep log-linear predictionDSR creep log-linear predictionShell sliding plate log-linear prediction


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— 27 —


Figure 4.11: Viscosity at 45 °C low viscosity oil – RAP1 blends

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osity

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DSRT/F sweepDSR CreepShell sliding plateDSR T/F sweep log-linear predictionDSR creep log-linear predictionShell sliding plate log-linear prediction

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osity

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DSR T/F sweepDSR CreepDSR T/F sweep log-linear predictionDSR creep log-linear prediction


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— 28 —

Figure 4.12: Viscosity at 45 °C low viscosity oil – RAP2 blends

4.4 Viscosity at 60 °C The capillary viscosity at 60 °C is a key parameter used in the specification of bitumen grades in Australia. To obtain a capillary viscosity measurement for RAP binder blends requires a substantial amount of RAP binder to be extracted, which is costly. As mentioned before, the DSR requires about 1 gram of binder per test. This section explores the use of the DSR to obtain a comparable viscosity measurement.

Figure 4.13 shows the results for the viscosity at 60 °C as measured using the capillary viscometer and the DSR at an angular frequency of 1 rad/s. The average capillary viscosity result for the Class 170 bitumen is 179 Pa.s, the average DSR measured viscosity 188 Pa.s. The average capillary viscosity result for the Class 320 is 305 Pa.s, the average DSR result 295 Pa.s. A summary of the viscosity at 60 °C results from the capillary viscometer and DSR is shown in Table 4.2. The DSR setting of 1 rad/s was chosen arbitrarily to some extent, but mainly for the following reasons:

The shear rate in the capillary viscometer is not constant; it differs per bitumen source, and between binder classes. Figure 4.14 shows some shear rate data measured in capillary viscosity tests at the ARRB laboratory. It would also differ per RAP source and blend. Therefore, even if the shear rate for a virgin binder could be replicated in the DSR, it would have to change as more RAP is added to the blend. This is impossible as the shear rate would not be known without performing the capillary viscosity test, which defeats the purpose of this investigation.

The 1 rad/s setting in the DSR yields a viscosity result similar to that of the capillary viscometer.

The aim of this exercise is not to replicate the capillary viscosity test, but to obtain an equivalent ranking test.

1

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osity

[Pa

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Percentage RAP

DSR T/F sweepDSR creepDSR T/F sweep log-linear predictionDSR creep log-linear prediction


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— 29 —

Figure 4.13: Comparison of viscosity readings from the DSR and capillary viscometer

Figure 4.14: Shear rate data from historic capillary viscosity tests

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250

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400

0 1 2 3

Visc

osity

[Pa

s]DSR 1 rad/sCapillary viscosityC170 viscosity rangeC320 viscosity range

C170 C320


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— 30 —

Table 4.2: Summary of viscosity at 60 °C results from the capillary viscometer and DSR at 1 rad/s

Binder Capillary viscosity 60 °C (Pa.s) DSR complex viscosity (η*) at 60 °C 1 rad/s (Pa.s) Test 1 Test 2 Average Test 1 Test 2 Average

C170 176 181 178 194 182 188

C320 303 307 305 288 302 295

Low viscosity oil 0.69 0.66 0.67

RAP1 4 611 6 806 5 708

RAP2 38 186 29 054 33 620

The viscosities at 60 °C as measured with the DSR (1 rad/s) for blends of C170 with RAP1 and RAP2 are shown in Figure 4.15 and Figure 4.16 respectively. The capillary viscosity results for the virgin binder are included in the figure. The figures further show the viscosity specification ranges for C170 and C320. The results indicate that for the RAP sources under study, a blend of C170 with 10% to 20% RAP does result in a viscosity equivalent to C320, as generally accepted in current practice.

The dip in viscosity for the blend of C170 with 10% RAP visible in Figure 4.16 is believed to be due to a testing error.


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osity

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DSR T/F sweepCapillary viscosityDSR T/F sweep log-linear predictionC170 viscosity rangeC320 viscosity range


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— 31 —


The viscosity at 60 °C from the DSR and capillary viscometer for the blends containing C320 and different percentages of RAP are shown in Figure 4.17 for RAP1 and Figure 4.18 for RAP2. The results indicate that the trend in the increase of viscosity with RAP content for RAP1 blends cannot be satisfactorily modelled using a simple exponential function. Other more suitable models will be fitted in Section 5. The results also indicate that even at 10% RAP content, the viscosity of the blend containing RAP2 is outside the specification range of a C320.


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osity

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DSR T/F sweepCapillary viscosityDSR T/F sweep log-linear PredictionC170 viscosity rangeC320 viscosity range

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osity

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DSR T/F sweepCapillary viscosityDSR T/F sweep log-linear predictionC320 viscosity range


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— 32 —


Figure 4.19 and Figure 4.20 show the viscosity at 60 °C results for blends of low viscosity oil with various percentages of RAP1 and RAP2. As before, the tests results shown were obtained at an angular velocity of 1 rad/s in the DSR. Also shown in the graph are the viscosity ranges for Class 170 and Class 320 bitumen, providing an indication of the proportion of RAP to oil that would result in a blend viscosity equivalent to these bitumen classes. As was the case for the viscosity results at 45 °C, the simple exponential model fitted to the data provides a poor fit for the blends containing low viscosity oil. The fit of alternative viscosity models from literature will be evaluated in Section 5.

Figure 4.19: Viscosity at 60 °C for low viscosity oil – RAP1 blends

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osity

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DSR T/F sweepCapillary viscosityDSR T/F sweep log-linear predictionC320 viscosity range

0.1

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osity

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DSR T/F sweepDSR T/F sweep log-linear predictionC170 viscosity rangeC320 viscosity range


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— 33 —

Figure 4.20: Viscosity at 60 °C for low viscosity oil – RAP2 blends

4.5 Discussion of Results One of the main findings from the experimental work is that viscosity testing using the DSR has significant advantages over conventional methods of characterising binder blends containing RAP. Although the DSR provides a measure of viscosity which tends to be lower than that obtained using the Shell sliding plate, the results from the DSR are more repeatable. In addition, the difference in log viscosity between the two methods for specific binder/RAP binder blends is reasonably consistent for varying percentages of RAP binder. The DSR is more cost effective than the capillary viscosity and penetration tests, as it requires significantly less extracted binder.

The DSR equipment is also more versatile than other viscosity test methods. It can be used to produce master curves for the binder blend, which in turn can be used to estimate the viscosity of the binder at any combination of temperature and loading time.

The relationships between viscosity and RAP content recorded in the experiments will be used to validate the predictive performance of various available blend viscosity prediction models in Section 5. Such models could be used by asphalt practitioners to design a blend containing RAP to a desired viscosity.

0.1

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osity

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DSR T/F sweepDSR T/F sweep log-linear predictionC170 viscosity rangeC320 viscosity range


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— 34 —

5 BLEND VISCOSITY PREDICTION In the previous section, a simple exponential model was used to approximate the trend between viscosity and RAP content of binder blends. The approach provided a poor fit to data for some of the blends. In this section, various models available from literature, including the model currently in the Austroads Guide, are fitted to the data and their predictive performance compared. The model that provides the best fit is then used to design a blend containing RAP, virgin binder and low viscosity oil to a desired viscosity.

5.1 Comparing Viscosity Prediction Rules There are many blending rules for the prediction of the viscosity of petroleum fractions available from literature. Centeno et al. (2011) presented an overview of the predictive performance of seventeen of these blending rules. Some of these rules require additional parameters that are not readily available to asphalt mix designers. Two blending rules were selected to be compared with the blending rule in Equation 1 currently included in the Austroads Guide. The first equation to be evaluated is the widely used Chevron equation shown here as Equation 9. It was one of the few equations deemed to provide acceptable accuracy by Centeno et al. (2011). The second equation to be assessed is a mixing rule for ideal liquids taken from Kendall and Monroe (1917) shown as Equation 10.

The Chevron equation requires the volume fraction of the different blend constituents to be calculated. In this study it is assumed that the density of the various virgin bitumen samples and the RAP is the same. The difference between the density of the bitumen and the low viscosity oil is also neglected as the density of bitumen is typically 1030 kg/m3, while the density of low viscosity oil used in this study is 1020 kg/m3. It is therefore assumed for the material under study that the percentages by volume are equal to percentages by weight.

𝑉𝐵𝐼𝑖 =log𝜗𝑖

3 + 𝑙𝑜𝑔𝜗𝑖

𝑉𝐵𝐼𝛽 = � 𝑥𝑖𝑉𝐵𝐼𝑖𝑛

𝑖=1

𝜇 = 10�3 𝑉𝐵𝐼𝛽1−𝑉𝐵𝐼𝛽

�

9

where

𝜗𝑖 = viscosity of ith component (cP)

𝑉𝐵𝐼𝑖 = viscosity blending index of ith component

𝑉𝐵𝐼𝛽 = viscosity blending index of the blend

𝑥𝑖 = volume fraction of ith component

𝜇 = viscosity of the blend (cP)

𝜇1 3� = 𝑤𝐴𝜇𝐴13� + 𝑤𝐵𝜇𝐵

13� 10


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— 35 —

where

𝜇 = viscosity of the blend (cP)

𝜇𝐴 = viscosity of component A (cP)

𝜇𝐵 = viscosity of component B (cP)

𝑤𝐴 = weight fraction of component A

𝑤𝐵 = weight fraction of component B

The fit of the three different equations for the blend viscosity data produced in this study is shown in Figure 5.1, Figure 5.2 and Figure 5.3.

Figure 5.1: Fit of different models for a) viscosity at 45 °C for C170 and RAP1, b) viscosity at 45 °C for C170 and RAP2, c) viscosity at 60 °C for C170 and RAP1, d) viscosity at 60 °C for C170 and RAP2

a) b)

c) d)


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— 36 —

Figure 5.2: Fit of different models for a) viscosity at 45 °C for C320 and RAP1, b) viscosity at 45 °C for C320 and RAP2, c) viscosity at 60 °C for C320 and RAP1, d) viscosity at 60 °C for C320 and RAP2

Figure 5.3: Fit of different models for a) viscosity at 45 °C for oil and RAP1, b) viscosity at 45 °C for oil and RAP2, c) viscosity at 60 °C for oil and RAP1, d) viscosity at 60 °C for oil and RAP2

a) b)

c) d)

a) b)

c) d)


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— 37 —

All three of the equations provide acceptable fits for the viscosity data for the blends containing C170 and RAP in Figure 5.1 and the blends containing C320 and RAP in Figure 5.2. There is little to set the equations apart for the blends containing virgin binder, all yield very similar predictions of the relationship between RAP content and viscosity. The trend for the blends of RAP with low viscosity oil has a different shape however. As can be seen from Figure 5.3a and b, the equation proposed by Kendall and Monroe provides a better fit to the viscosity at 45 °C data compared to the other two models. For the viscosity at 60 °C however, the shape of the Kendall and Monroe model becomes unrealistic. Overall, data for this study indicates that the predictive performance of the Chevron equation is similar to that of the current Austroads equation. The accuracy and consistency of the predictions is acceptable, but the models do over-estimate the viscosity of the blends containing low viscosity oil to a degree.

5.2 Designing Blends to a Desired Viscosity To show the practical use of the viscosity prediction equations a final round of laboratory experiments was performed with the aim of designing a binder blend to meet a target viscosity. The Chevron equation was selected to be used for this purpose. The Chevron equation was selected over the current Austroads equation for the following reasons:

The Chevron equation appears to be slightly more sensitive and accurate than the current Austroads equation.

To allow for more than two components in a binder blend, e.g. virgin binder, RAP and rejuvenator, the current Austroads equation would have to be rewritten into a form that allows for this. The current equation in the Austroads Guide is not widely used, and therefore it may as well be replaced.

The aim of the binder blend design was to create a blend containing a relatively high RAP content, combined with C170 and low viscosity oil proportioned such that the viscosity at 60 °C met the requirements for C320, i.e. 260–380 Pa.s.

In the initial design for a blend containing RAP1, the RAP content was set to 50%, with 40% C170 and 10% low viscosity oil. The calculation of the combined viscosity of this blend is shown in Equation 11, using the viscosity at values from the DSR at 60 °C and 1 rad/s from Table 4.2. The predicted viscosity of the blend is 368 Pa.s, which is within the C320 specification range and therefore no further adjustments were made to the proportions. Again note that differences in density need to be taken into consideration when calculating the volume proportions. For the binders under study, the density differences are negligible.

𝑉𝐵𝐼𝑅𝐴𝑃 = log(5708000)3+log (5708000)

= 0.693

𝑉𝐵𝐼𝐶170 =log(188000)

3 + log (188000)= 0.637

𝑉𝐵𝐼𝑜𝑖𝑙 =log(670)

3 + log (670)= 0.485

𝑉𝐵𝐼𝛽 = 0.5 × 0.693 + 0.4 × 0.637 + 0.1 × 0.485 = 0.650

𝜇 = 10�3 ×0.6501−0.650� = 367672 cP = 368 Pa. s

11


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A blend containing 50% of RAP2 was designed as well. For comparison purposes it was decided to target a similar viscosity to the blend containing RAP1. The composition of this blend was set to 50% RAP, 33% C170 and 17% low viscosity oil. The predicted viscosity for the blend calculated using Equation 9 was 380 Pa.s. The viscosity values for the designed blends are shown in Table 5.1. The accuracy of the prediction is very high for blend 1, which is probably to at least a degree due to coincidence and not reflective of the overall accuracy of the model. The accuracy of the prediction for blend 2 is not as high as for blend 1, but nonetheless very acceptable.

Table 5.1: Complex viscosity at 60 °C, 1 rad/s for design blends

Test 1 η* (Pa.s)

Test 2 η* (Pa.s)

Average η* (Pa.s)

Predicted η* (Pa.s)

Blend 1 361 369 365 368

Blend 2 329 331 330 380

The results show that the methodology developed in this study may be used to design binder blends for asphalt mixes containing RAP to a desired viscosity.


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6 CONCLUSIONS AND PROPOSED BLEND SPECIFICATION GUIDELINE

The overall objective of this study is to maximise the re-use of reclaimed asphalt pavement (RAP) in asphalt pavements in Australia, and in doing so, maximise the economic and sustainability benefits to be gained from the re-use of RAP.

The aim in this first year of the three year Austroads project was to improve the methodology for the characterisation of RAP binders and the design of the binder blend in asphalt mixes containing RAP.

The second year of the study will focus on the performance of asphalt mixes containing different percentages of RAP. The design guidelines for mixes containing RAP will be updated based on the results of these experiments and a study of international best practice.

The objectives for the final year of study are only tentative at this stage. The envisaged objective will be to develop guidelines for the design of high performance mixes containing high percentages of RAP.

6.1 Conclusions The literature review performed as part of the study found that the Australian approach to accounting for the increase in viscosity of the binder blend due to the use of RAP is broadly in line with international best practice. This is true both on a national level in terms of the methodology proposed in the Austroads Asphalt Recycling guidelines AP-T66/06 (Austroads 2006), and on a state level in terms of the requirements set by road agencies for the use of different proportions of RAP in mixes. Characterisation of the properties of the blend of RAP and virgin binder is currently not part of standard practice in Australia. In some cases, the viscosity of the blend is corrected by adding a softer binder, but typically without checking the viscosity of the final product. Internationally, the characterisation of the properties of the extracted RAP binder, and design of an appropriate blend of RAP and virgin binder is often required, even at relatively low percentages of RAP in the final mix. It was also found that limited use is being made of the binder viscosity prediction model in AP-T66/06 and the requirements for binder blends set in that document.

The experimental work showed that the Dynamic Shear Rheometer (DSR) can be used for viscosity measurement as an alternative to both the Shell sliding plate test (viscosity at 45 °C) and the capillary viscosity test (viscosity at 60 °C). Although the DSR results for viscosity at 45 °C tend to be lower than those obtained using the Shell sliding plate, the DSR results are more repeatable than those of the Shell sliding plate test, which has conventionally been a common test used in Australia for the characterisation of RAP binder

The results show that for the RAP sources under study, a blend of C170 with 10% to 20% RAP does result in a viscosity equivalent to C320, as sometimes assumed in current practice.


The methodology developed in the study can be applied in the design of conventional asphalt mixes containing RAP, as well as in the process to design the final product for hot-in-place recycling operations.


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Note that even though the DSR was used in this study, the same methodology could be applied to design binder blends at desired viscosity using other viscosity test methods, such as the cappillary viscometer.

Also note that even though blends of fresh bitumen and RAP were investigated in this study, the same methodology could be applied to design binder blends based on after RTFOT viscosity properties. The changes required to the procedure to enable this would be to RTFO treat the virgin binder as well as the extracted RAP binder before running the viscosity tests.

6.2 Guideline for RAP Binder Blend Design and Specification Based on the work in the report a guideline for the specification and design of RAP binder blends is proposed. It is proposed that if a mix design contains more than 10% RAP, the properties of the binder blend containing the RAP binder, the virgin binder, and rejuvenator if applicable, should be determined using the following procedure:

Collect a representative sample of the RAP in accordance with AS 1141.3.1.

Determine the binder content of the RAP in accordance with AS 2891.3.3.

Extract a representative sample of the RAP binder in accordance with ARRB method M 07, or equivalent.

Determine complex viscosity of the RAP, the virgin binder, and rejuvenator in the DSR at 60 °C, at 1 rad/s, in accordance with AASHTO T315-12.

Predict the viscosity of the blend using Equation 9.

If the viscosity is outside the desired range for the design, adjust the proportion of the binder blend components with the help of Equation 9.

Check the viscosity of the final design blend directly using the DSR.

At this stage it is proposed that the normal AS 2008-1997 viscosity ranges are targetted when designing a binder blend, i.e. 260 to 380 Pa.s to create an equivalent Class 320 bitumen and 500 to 700 Pa.s for a binder equivalent to Class 600.


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REFERENCES AAPA 2004, National asphalt specification, 2nd edn, Australian Asphalt Pavement Association, Kew, Vic.

AASHTO 2009, Standard method of test for determining the rheological properties of asphalt binder using a dynamic shear rheometer (DSR), T315-10, American Association of State Highway and Transportation Officials, Washington, DC, USA.

Alderson, A 1995, ‘Asphalt recycling survey’, workshop on pavement recycling, Newcastle, Australia, ARRB Group, Vermont, South..

Al-Qadi, I, Elseifi, M & Carpenter, S 2007, Reclaimed asphalt pavement: a literature review, Illinois Center for Transportation, Urbana, IL, USA.

Arnold, J, Noltling, M, Riebesehl, G & Denck, C 2012, ‘Unlocking the full potential of reclaimed asphalt pavement (RAP): high quality asphalt courses incorporating more than 90% RAP: a case study’, Proceedings of the 5th Eurasphalt & Eurobitume congress, Istanbul, 13-15 June 2012, European Bitumen Association, Brussels, Belgium.

ARRB Group 2005, Extraction of bituminous binder from sprayed seal and bituminous concrete samples: adapted from ARR 66, ARRB method no. M07, ARRB Group, Vermont South, Vic.

Asphalt Institute 1986, Asphalt hot-mix recycling, manual series no. MS-20, 2nd edn, Asphalt Institute, College Park, Maryland, USA.

Austroads 2002, Austroads framework for specifying asphalt, APT-18/02, Austroads, Sydney, NSW.

Austroads 2006, Asphalt recycling, APT-66/06, Austroads, Sydney, NSW.

Austroads 2007, Guide to pavement technology: part 4B: asphalt, AGPT04B/07, Austroads, Sydney, NSW.

Austroads 2010, Glossary of Austroads terms, 4th edn, AP-C87/10, Austroads, Sydney, NSW.

Austroads 2013, Development of long-term ageing test method for sprayed sealing binders, AP-T225/13, Austroads, Sydney, NSW.

Bowering, R 1991, ‘Asphalt recycling in Australia: 1990’, working document RI91/002, Australian Pavement Research Group, Australian Road Research Board, Vermont South, Vic.

Bukowski, J 1997, Guidelines for the design of Superpave mixtures containing reclaimed asphalt pavement (RAP), University of Texas, Austin, TX, USA.

Carey, D & Paul, H 1980, Effects of asphalt cement rejuvenating agents: final report, FHWA/LA-80/146, Louisiana Department of Transportation and Development, Baton Rouge, Louisiana, USA.

Carpenter, S & Wolosick, J 1980, Modifier influence in the characterization of hot-mix recycled material, Transportation Research Record, vol. 777, pp. 15-22.

Centeno, G, Sanchez-Reyna, G, Ancheyta, J, Munoz, JAD & Cardona, N 2011, ‘Testing various mixing rules for calculation of viscosity of petroleum blends’, Fuel, vol. 90, no. 12, pp. 3561-3570.

Chaffin, J, Davison, R, Glover, C & Bullin, J 1995, Viscosity mixing rules for asphalt recycling, Transportation Research Record, vol. 1507, pp. 78-85.

CROW 2011, Asfalt in weg- en waterbouw, publicatie 285, (in Dutch), CROW, Ede, The Netherlands.


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Department of Construction and Infrastructure 2010, Road master specification T09: dense graded asphalt, Northern Territory Government

Department of Infrastructure, Energy and Resources 2011, Road specification R55: asphalt placement, DIER, Hobart, Tas.

Department of Planning, Transport and Infrastructure 2010, Specification: part 227: supply of asphalt, DPTI, Adelaide, SA.

Department of Transport and Main Roads 2010, Standard specifications roads: MTRS 30: dense graded and open graded asphalt, TMR, Brisbane, Qld.

Department of Transport and Main Roads 2011, Standard specifications roads: MTRS 31: heavy duty asphalt, TMR, Brisbane, Qld.

European Asphalt Pavement Association 2010, Asphalt in figures, EAPA, Brussels, Belgium.

Epps, JA, Little, RJ & Terrel, RL, 1980, Guidelines for recycling pavement materials, NCHRP report 224, TRB. National Research Council, Washington, DC, 1980.

Federal Highway Administration 2011, Statistical analysis of performance of recycled hot-mix asphalt overlays in flexible pavement rehabilitation, FHWA, McLean, Virginia, USA.

Haligan S & Chatard S 2010, Use of dynamic shear rheometer for the bitumen durability test feasibility study. Material Engineering report No 2010-5M, Main Roads Western Australia.

Holtrop, W & Alderson, A 1995, ‘Asphalt recycling survey results’, APRG 95/08, ARRB Transport Research, Vermont South, Vic.

Ipavec, A, Marsac, P & Mollenhauer, K 2012, ‘Synthesis of the European national requirements and practices for recycling in HMA and WMA (DIRECT MAT project)’, Proceedings of the 5th Eurasphalt & Eurobitume congress, Istanbul, 13-15 June 2012, European Bitumen Association, Brussels, Belgium.

Kendall, J & Monroe, K 1917, ‘The viscosity of liquids II: viscosity-composition curve for ideal liquid mixtures’, American Chemistry Journal, vol. 39, no. 9, pp. 1787-1802.

Kennedy, TW, Huber, GA, Harrigan, ET, Cominsky, RJ, Hughes, CS, Von Quintus, H & Moulthrop, MS 1994, Superior performing asphalt pavements (Superpave): the product of the SHRP Asphalt Research Program, Strategic Highway Research Program, Washington, DC, USA.

Kennedy, TW, Tam, W & Solaimanian, M 1998, Effect of reclaimed asphalt pavement on binder properties using the Superpave system, research report no. 1250-1, University of Texas, Austin, TX, USA.

Mangiafico, S, Di Benedetto, H, Sauzeat, C, Olard, F, Pouget, S, Planque, L 2012, ‘Viscoelastic properties of bitumen blends obtained from pure and RAP extracted binders’, Eurasphalt & Eurobitume congress, 5th, 2012, Istanbul, Turkey, European Bitumen Association, Brussels, Belgium.

Main Roads Western Australia 2013, Specification 510: full depth asphalt pavement, document 07/5856, MRWA, Perth, WA.

McDaniel, R & Anderson, RM 2001, Recommended use of reclaimed asphalt pavement in the Superpave design method: technician's manual, NCHRP report 452, Transportation Research Board, Washington, DC, USA.


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McDaniel, R, Soleymani, H, Anderson, RM, Turner, P & Peterson, R 2000, Recommended use of reclaimed asphalt pavement in the Superpave mix design method, NCHRP web document 30, Transportation Research Board, Washington, DC, USA.

McDaniel, R, Soleymani, H & Anderson, RM 2001, Recommended use of reclaimed asphalt pavement in the Superpave mix design method: guidelines, research results digest no. 253, Transportation Research Board, Washington, DC, USA.

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A u s t r o a d s 2 0 1 3

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Standards Australia

AS 2341.3-1993, Methods of testing bitumen and related roadmaking products: determination of kinematic viscosity by flow through a capillary tube.

AS 2341.5-1997, Methods of testing bitumen and related roadmaking products: determination of apparent viscosity by 'Shell' sliding plate micro-viscometer.

AS 1141.3.1-2012, Methods for sampling and testing aggregates: sampling: aggregates.

AS 2008-1997, Residual bitumen for pavements.

AS 2891.3.3-1997, Methods of sampling and testing asphalt: bitumen content and aggregate grading: pressure filter method.

European Committee for Standardization

EN 13108-1: 2008, Bituminous mixtures: material specifications: part 1: asphalt concrete.

EN 13108-8: 2008, Bituminous mixtures: material specifications: part 8: reclaimed asphalt.

INFORMATION RETRIEVAL

Austroads, 2013, Maximising the Re-use of Reclaimed Asphalt Pavement: Binder Blend Characterisation, Sydney, A4, pp.47. AP-T245-13.

Keywords: reclaimed asphalt pavement (RAP), dynamic shear rheometer (DSR), RAP binder blend characterisation, viscosity prediction.

Abstract:

This report presents the findings from the first year of a three year Austroads study which aims to maximise the re-use of reclaimed asphalt pavement (RAP) in new asphalt product. The objective of this first year of study is to improve the methodology for the characterisation of RAP binders and the design of the binder blend in asphalt mixes containing RAP.

The study included a literature survey of the current international state of practice in terms of RAP binder characterisation. It further included experiments to develop a more practical and cost-effective approach to characterising the properties of binder blends containing RAP. The experimental work showed that the Dynamic Shear Rheometer (DSR) can be used to obtain viscosity parameters similar to the Shell sliding plate viscosity at 45 °C and the capillary viscosity at 60 °C. The DSR results are also more repeatable than the results of the Shell sliding plate test, which has conventionally been a more common test used in Australia for the characterisation of RAP binder.

The results show that for the RAP sources under study, a blend of C170 with 10% to 20% RAP does result in a viscosity equivalent to that of a C320, as generally accepted in current practice.


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AP-T245-13

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