RAP Mixtures Research Articles

Laboratory evaluation and FEM modeling of the rutting behavior of CR-enriched rejuvenator-modified RAP mixtures

Laboratory evaluation and FEM modeling of the rutting behavior of CR-enriched rejuvenator-modified RAP mixtures

Optimizing Rural Pavements with SBS-Modified Asphalt Binders and Petroleum Resin

This study addresses the imperative for enhancing asphalt mixtures tailored for rural pavements, focusing on optimizing RAP mixtures with styrene–butadiene–styrene (SBS)-modified asphalt binders incorporating petroleum resin and oil. Through systematic investigation, the study examines the impact of varying RAP content (25% and 50%) and two SBS-modified asphalt binder types (Type 1 and Type 2) on mechanical properties and sustainability. Laboratory tests reveal that the mix of 25% RAP + 75% Type 1 exhibits exceptional flexibility, evidenced by a high ductility value of 880 mm at 25 °C, enhancing pavement resilience. Conversely, the 50% RAP + 50% Type 2 mixture displays vulnerability to fatigue cracking, while 25% RAP + 75% Type 1 demonstrates superior resistance, with a fatigue vulnerability value of 1524 kPa. The Hamburg Wheel Tracking test highlights the influence of RAP content on rut depth, with the mix of 50% RAP + 50% Type 1 achieving the lowest rutting at 3.9 mm. Overlay test results show the mix of 25% RAP + 75% Type 2’s resilience, with the lowest load reduction at 64.5%, while the mix of 50% RAP + 50% Type 1 exhibits substantial load reduction at 82.1%. Field tests unveil differences in pavement bearing capacities, with the mix of 25% RAP + 75% Type 2 demonstrating a remarkable elastic modulus of 58.5 MPa, indicating heightened bearing capacity. The investigation underscores the significant role of SBS-modified asphalt binders with incorporated petroleum resin and oil in enhancing fatigue resistance for sustainable rural pavements.

Laboratory Evaluation of Short- and Long-Term Aging Resistance of Rejuvenated RAP Mixtures

Laboratory Evaluation of Short- and Long-Term Aging Resistance of Rejuvenated RAP Mixtures

Innovative 100% RAP cold in-situ recycling of wearing course layers: laboratory and field characterisation and environmental impact assessment

ABSTRACT In the last decade, research is pushing forward the use of innovative techniques and environmentally friendly materials aiming at sustainable development in the road sector. In the present paper, a 100% RAP mixture is proposed through an innovative cold recycling in-situ technique for road pavement maintenance of small damaged sections and repairing distresses. The localized patching is developed through an innovative milling machine that is capable of directly and simultaneously milling and mixing the RAP produced. The innovative machine develops repairs that guarantee the safety and comfort of users. For obtaining the final mixture, RAP is combined with cement and a chemical additive. The experimental program was divided into a laboratory study of the milled material and a trial field campaign. After these phases, the environmental impacts that affect the repaired road sections are also evaluated through Life Cycle Assessment (LCA) tool. Tests from the laboratory and field phase highlighted positive results and downsides that need to be optimized to obtain a good quality intervention. The LCA analysis showed a positive impact in terms of global warming potential. Thanks to the use of this innovative machine, it is possible to mitigate the negative environmental impact associated with road pavement maintenance.

Impact of aggregate structure restoration on rutting resistance of asphalt mixtures with very high percentages of RAP

ABSTRACT Bailey method is a well-proved method to build strong aggregate structure, but it is originally devised to do so by proportioning the fractionated virgin aggregate stockpiles. Yet, the concepts of strong aggregate structure in the Bailey method stand true in any type of aggregate. This study develops a method for correcting the bad gradation of RAP by utilising Bailey’s concepts. The virgin aggregate stockpiles are added minimally into RAP to establish a firm aggregate skeleton. This changes the philosophy of aggregate blend design from the RAP following an existing good gradation to the RAP gradation correction. The effectiveness of the method was evaluated by the indirect tensile (IDT) strength and laboratoire des ponts et chaussées (LPC) wheel tracking tests. The mixtures whose gradations were rectified by this method, whether coarse dense-graded (CDG) or fine dense-graded (FDG), have significantly higher rutting resistance than 100% RAP mixture.

Life Cycle Assessment of road pavements rehabilitation re-using high content of Reclaimed Asphalt Pavement

The main objective of the paper is to assess the viability of the re-use of RAP mixtures as a solution for road pavement rehabilitation combining mechanical, functional and environmental aspects. To evaluate the environmental impact a Life Cycle Assessment (LCA) was performed considering a real pavement section. The LCA was carried out on two scenarios that stem from the combination of production, construction and maintenance operations: one that considers 75% RAP incorporation in new asphalt mixture; and another as the reference solution with virgin raw materials. The mechanical behavior was evaluated by determining the stiffness, water sensitivity and permanent deformation. The functional performance was evaluated through the macrotexture and skid resistance. Significative gains were observed in LCA. RAP mixtures showed as a viable alternative to virgin solutions.

Evaluation of Incorporating CKD and RAP on the Performance of Cohesive Soil

The aim of this study is to investigate the effect of adding recycled materials such as CKD and RAP to weak cohesive soils, in addition to evaluate the change in the strength of these soils. This study was conducted on soil type MH, and only RAP particles finer than 10 mm were used in preparing the mixtures. 7, 14, and 28 days were selected as curing periods for soil- CKD and soil- CKD- RAP mixtures to obtain the effect of curing periods on soil improvement. The results showed that adding 20% of CKD to the natural soil increased the unconfined compression strength UCS from 0.43 MPa to 2.6 MPa at a 28-day curing period. Also, the results showed that adding 25% of RAP to the soil- 20% CKD mixture increased the UCS value to 5.3 MPa after 28 days of the curing period. The final results showed that the optimum contents of CKD and RAP added to the cohesive soil were 20% and 25%, respectively, while the optimum curing period was 28 days

Assessment of the Effect of Nono-clay on Recycled Asphalt Mixtures Resistance to Moisture

Introducing nanotechnology to the pavement industry witnessed a great interest due to the proven benefits of nanotechnology in various scientific fields. However, the reduction in the binder's characteristics might be disadvantageous to the durability of the recycled mixture, making it more susceptible to external factors such as moisture. Therefore, using nanotechnology is expected here to treat this issue. The goal of the current paper is to report on the influence of the nano-clay montmorillonite (MMT) powder (MMT k10) on the resistance to moisture in the hot recycled mixtures or the Reclaimed Asphalt Pavement mixtures (RAP mixtures). In this work, different proportions of rejuvenated RAP were employed. These proportions are 30, 40, and 50% as a percent of the overall weight of the mix. The percentages were mixed with a nano-modified neat binder with (0, 1, 3, and 5)% nono-clay MMT as a proportion of the bitumen’s weight. Two types of mixtures are prepared and used in this paper: nano-modified RAP mixtures and unmodified RAP mixtures. On both types of mixtures, the compressive strength test, the index of retained strength (IRS), the indirect tensile strength tests (ITS), and the tensile strength ratio (TSR) were carried out to compare and evaluate the moisture resistance of rejuvenated RAP mixtures. The experimental test results indicated that using 5 percent nono-clay in regenerated RAP mixes provides better performance than not using it. where it increased moisture damage resistance by5.53% for IRS value and 3.66% for TSR for 50 percent RAP mixes.

Assessing RAP Multi-Recycling Capacity by the Characterization of Recovered Bitumen Using DSR

This paper addresses the changes in bitumen properties during multi-recycling cycles, both before and after ageing. The rheology of recovered bitumen was characterized using the dynamic shear rheometer. The softening point and penetration value were also determined. The analysis showed that the bitumen’s properties could be recovered even after more than one recycling cycle. The bitumen recovered from the second recycling cycle presented an average reduction of 45% in terms of complex modulus when compared with the first recycling cycle. The bitumen from the RAP mixtures presented a similar susceptibility to ageing. The analysis clearly showed that RAP has the potential to be multi-recycled.

Comprehensive Laboratory Evaluation of Recycling Agent Treated Plant-Produced Asphalt Mixtures

Recycling agent (RA) is typically used to restore or rejuvenate the properties of aged asphalt to desired properties. This study was motivated to comprehensively characterize the performance of asphalt mixtures treated with RA. The overarching goal of the research project is to provide guidance to agencies for revising asphalt mixture specifications to include RAs. Ten plant-produced mixtures were evaluated including three control mixtures (with 30 and 40% reclaimed asphalt pavement [RAP]) and seven 40% RAP mixtures treated with different RA products. Mixture testing was conducted with and without laboratory conditioning of loose mixture for 6 h at 135°C. Testing included the mixture Complex Modulus (E*) test for viscoelastic characterization, Direct Tension Cyclic Fatigue test for fatigue performance evaluation, Tensile Strength Ratio test for moisture susceptibility evaluation, and Semi-circular Bending test, Cracking Index Test and Disk-shaped Compact Tension test for mixture cracking and fracture behavior at different temperatures. In addition, the Hamburg Wheel Track Testing was conducted for rutting performance characterization on the unaged mixtures. Results show that addition of different RAs can improve the properties of asphalt mixtures by softening the mixtures with RAP and improving the cracking performance as compared with the control mixtures. However, addition of RA could severely deteriorate the rutting performance of mixtures and increase the moisture susceptibility as compared with the control mixtures. In addition, addition of certain RAs can also decrease the aging resistance of asphalt mixtures, specifically in context of cracking performance.

Investigating aged binder mobilization and performance of RAP mixtures for surface courses

Pavement engineering practice still deals with a set of restraints regarding the use of RAP, mainly in the case of bituminous surface courses. The main objectives of this paper are to assess: (a) the influence of the rejuvenator and the degree of aged binder mobilization on the homogeneity of bituminous mixtures; and (b) the performance and durability of bituminous mixtures for surface courses with 25% RAP. The laboratory investigation studied an AC 14 surf 35/50 considering two mixture compositions: a reference mixture with virgin constituents; and a mixture containing RAP and a rejuvenator agent. The study was focused on the mechanical and functional behaviours, as well as on the short- and long-term ageing performance of mixtures. An experimental protocol for RAP fractioning and rejuvenator addition was established to achieve a better control of the final mixture quality. The aged binder mobilization was more efficient when RAP was heated. The RAP mixture revealed a good performance in terms of permanent deformation, water sensitivity, stiffness, and fatigue. The incorporation of fractionated RAP allowed to have a mixture with good surface characteristics. Aged RAP mixture performance envisioning good long-term behaviour. Regarding the promotion of the circular economy, this investigation clearly demonstrated that mixtures with a 25% RAP incorporation can be currently used in surface courses.

Effect of initial damage on healing characteristics of bituminous mixtures containing reclaimed asphalt material (RAP)

Fatigue damage healing of bituminous mixtures containing reclaimed asphalt pavement material (RAP) is of research interest since the healing ability of RAP mixtures is expected to be different from that of virgin mixtures which is due to the differences between the chemical properties of un-aged and aged binders. Very limited research work has been reported in the literature about the healing ability of RAP mixtures. Hence, the present study focuses on investigating the fatigue damage healing characteristics of RAP mixtures. For this purpose, blends of RAP and virgin binders (VG30) were prepared corresponding to varying proportions (0, 15, 25, 35 and 45%) of RAP material in the mix. RAP asphalt mix specimens were subjected to indirect tensile fatigue testing and were damaged to different levels of damage (25%, 50% and 75% of the total fatigue life). Different sets of specimens were healed by conditioning them at temperatures of 40 °C and 60 °C for a duration of four hours and were tested again for their fatigue lives. The healing potential of the mixes was evaluated in terms of fatigue life healing index (HIL) and modulus healing index (HIM). Results from the study indicated that the fatigue life of the mix increased with increase in the proportion of RAP in the mix. The two healing indices estimated from fatigue life and modulus value reduced with increase in the initial damage. The degree of healing was also found to depend significantly on the RAP content in the mix. However, there is no significant difference between the healing abilities of the mixes healed at 40 °C and 60 °C. Methyl and methylene hydrogen to carbon (MMHC) ratio and CH2/CH3 ratio were used to explain the healing characteristics of the mixes and were found to be correlated well with the fatigue life healing ability.

Investigation of the oxidation ageing of RAP asphalt blend binders and mixtures

ABSTRACT This study evaluates the oxidation ageing properties of asphalt blends and mixtures combined with various percentages of RAP and SBS-modified binder, rejuvenator and neat binder. Four ageing methods were conducted in the laboratory on the asphalt blends and mixtures. The results showed that the G-R parameter, the ICO and the flexibility index increased, while the ΔTcr decreased with the RAP content and the ageing level. The SBS-modified binder and rejuvenator improved the cracking resistance of the RAP binder and mixture. After PAV 20 h ageing, the asphalt blends containing a low amount of RAP were equivalent to their virgin binder after PAV 40 h ageing. The asphalt blends containing a low amount of RAP after PAV 40 h ageing were equivalent to their virgin binder after PAV 60 h ageing. It was found that binders subjected to RTFO, PAV 20 h ageing, PAV 40 h ageing, and PAV 60 h ageing had rheological and chemical properties equivalent to those of loose mixtures subjected to the STOA protocol for 4 h at 135°C, the LTOA protocol for 8 h at 135°C, the LTOA protocol for 12 h at 135°C, and the LTOA protocol for 24 h at 135°C, respectively.

Evaluation of solvents for asphalt extraction

The laboratory evaluation of the performance of a number of asphalt extraction solvents was conducted. The performance testing was conducted on unmodified and polymer modified asphalt binder with the Bitumen Degradation Test (BDT) and on polymer modified and RAP mixtures with centrifuge extraction. The chemical interaction between the binder and the solvent was analysed by Fourier Transform Infrared (FTIR) Spectrometry. Several commonly used extraction solvents were tested including trichloroethylene, dichloromethane, toluene and xylene along with a number of alternative agents. The alternative agents included chlorinated, petroleum-based and bio-sourced solvents. The chlorinated solvents (trichloroethylene-TCE, dichloromethane and two higher exposure limit candidate agents) were found to be the best solvents to dissolve the binder in the BDT. These solvents were tested in the final round with centrifuge extraction, where they were evaluated based on the ability to dissolve the binder and evaporate after the extraction. While TCE had the best performance, some candidates were found to perform almost as effectively as the trichloroethylene, making them viable alternatives to the latter.

Performance-based design of 100% recycled hot-mix asphalt and validation using traffic load simulator

Abstract This paper reports a comprehensive study on application of performance-based design method for design of 100% recycled asphalt wearing course mixture and demonstrates the performance of the optimum composition from mechanical, traffic safety and environmental points of view. An AC8 type mixture was designed by balancing performance in rutting using French rut tester and cracking using semi-circular bend test. Five iterations of different grading and binder content combinations of 100% RAP mixture were tested before achieving the same performance as a traditional AC8 mixture. This optimum mixture design was then validated by producing asphalt slabs for testing using a Model Mobile Load Simulator (MMLS3). Digital image correlation results of the wheel loading demonstrated that performance-optimized 100% recycled asphalt can sustain 2.5 times more load applications compared to the traditional mixture before cracking. This wearing course recycled asphalt mixture was then tested for skid resistance and particle abrasion due to rolling tires and achieved similar results to the reference mixture. The research allows concluding that the proposed mixture design approach can be successfully applied for designing 100% recycled asphalt mixtures that perform similar or better than traditional wearing course asphalt mixtures in all key domains and are safe to the traffic and the environment.

Evaluation of fatigue performance of high RAP-WMA mixtures

The present work investigates the influence of asphalt modifiers at the beginning of the fatigue process through the mixture damage accumulation. In this sense, this paper uses the Simplified Viscoelastic Continuum Damage (S-VECD) methodology to compare the fatigue performance of a 50% RAP warm mix asphalt (WMA) to a 50% RAP hot mix asphalt (HMA), and five different asphalt mixtures with and without modifiers. Results show that combining WMA (foaming process) with 50% RAP mixture significantly improved the fatigue performance of the mixture, including in comparison with an HMA using 100% virgin materials. Therefore, considering the advantages presented by a 50% RAP WMA, e.g. lower environmental impact, lower cost and good fatigue performance, the warm mix recycling is a promising alternative for performance optimization.

Effect of rejuvenator and mixing methods on behaviour of warm mix asphalt containing high RAP content

Rejuvenators are normally used in the hot in plant or hot in place recycling process of asphalt pavement. The use of rejuvenators in recycling RAP in warm mix asphalt (WMA) remains very limited. This study was carried out to investigate the use of a rejuvenator which was normally used for HMA, in producing WMA containing RAP. Laboratory tests were done on the binder rheological properties and the mechanical behaviours of the mixtures. Mechanical behaviours of WMA with RAP mixtures produced by the rejuvenator were compared with that of a control HMA and other WMA-RAP mixtures produced by using Evotherm WMA additive. Tests were carried out on resilient modulus, indirect tensile strength, semi-circular bending test, and four-point bending fatigue test. Results showed that it is possible to produce WMA by adding RAP and by using rejuvenators. WMA adding RAP mixtures produced with the rejuvenator performed better than WMA adding RAP produced with Evotherm additive in fatigue cracking resistance. The study further investigated the effect of different mixing methods of the rejuvenator with the binder on the mechanical properties of the WMA adding RAP mixtures. The study found that when the content of the RAP is lower than 50%, the mechanical behaviour of mixtures did not significantly change regardless of different mixing methods. However, when the content of the RAP is 50% or higher, adding the rejuvenator directly into the RAP significantly improved the moisture resistance of WMA RAP mixtures. For overall results, adding the rejuvenator into RAP was found more effective than adding the rejuvenator into the hot bitumen before mixing.

Fatigue Performance Analysis of Pavements with RAP Using Viscoelastic Continuum Damage Theory

This paper presents the results of a study to evaluate the fatigue performance of pavements that contain RAP materials. The study is based on two different accelerated loading tests conducted in the United States. Each of these two projects has corresponding pavements with and without RAP mixtures that were constructed over the same aggregate base and subgrade and subjected to the same traffic loading and environmental conditions. The primary reason for selecting these two projects is that they exhibited opposite trends in a comparison of the fatigue cracking performance of their pavements with and without RAP. The asphalt mixtures in the test pavements were characterized using the simplified viscoelastic continuum damage model. The fatigue cracking performance of the pavements was then modeled using the characterized material properties, in situ pavement structures and traffic loads, and climate conditions in FlexPAVE™, a three-dimensional layered viscoelastic finite element program with moving load analysis. The resultant fatigue cracking performance predictions matched the field observations well. Both the simulation results and the field observations also showed that the fatigue cracking performance of the asphalt mixtures that

The characteristics of asphalt mixture in the system of full thickness cold in-place recycling

A new research method was proposed(A/S method) to study the components and properties of reclained asphalt mixture (RAP). The RAP was divided into two main parts, one was marked with A that included all the reclaimed old asphalt materials(including some parts of particle materials covered by asphalt), the other was marked with S which mainly included works soil in the road structure. The actual working conditions were simulated by this kind of new method, and the adaption between the RAP properties, A/S, and the content of cementitious materials were studied. The research indicated that the real working condition could be simulated effectively by means of A/S method. It was also showed that high content of cement could improve the overall performance of RAP significantly, but it would have a negative effect on the properties of RAP if the types and sizes of aggregate particles in RAP mixture were too single. The optimum water content and maximum dry density could not be regarded as the primary basis to evaluate the overall performance of RAP, when S=0 in the experiments, although the maximum density of samples was bigger than that with A/S=1/1, the samples were not strong enough and they were easy to collapse, which indicated that component design of RAP played a great role in improving the overall properties of RAP and the comprehensive tests should be considered to evaluate the stability of RAP. Low frequency load in high temperature environment had the negative effect on the overall stability of RAP, and factors such as the loading state of the materials, the hydration degree of cementitious materials, and the aggregate gradation in the mixture were the determining factors for improving the overall performance of RAP.

Rheological behavior of cold recycled asphalt materials with different contents of recycled asphalt pavements

In Quebec, for more than 20 years, cold in-place recycling (CIR) and full-depth reclamation (FDR) have been reliable rehabilitation techniques; restoring pavement condition at an affordable cost with a lower footprint on the environment. Experience reveals that CIR and FDR interventions effectively address the issues of reflective cracking and respect Quebec’s Ministry of transportation rutting threshold values. However, despite their commendable performance in the field, the cold recycled emulsified asphalt materials (CRM) has yet to be adequately characterized with respect to their rheological properties. This study was undertaken to evaluate the rheological behavior of the CRM with four different combinations of RAP (50, 75, 85, and 100%). The scope of work for this study consisted of preparing the laboratory compacted CRM specimens, determining the complex modulus (E*) of compacted specimens at various testing temperatures and loading frequencies, analyzing the experimental data with the help of 2S2P1D (2S: two springs, 2P: two parabolic elements, 1D: one dashpot) model and finally, validating the results with pavement design. It was concluded that 100% RAP mixture exhibits extremely high stiffness value at high frequency and low temperature. The results revealed that all four mixtures respect the time–temperature superposition principle with respect to the complex modulus. From a pavement design perspective, the moduli measured in this study do have a big impact. However, since different pavement structure are achieved with those different materials, the stiffest material, the CIR, ended up giving the least performant structure.