Recycled Asphalt Pavement Mixes Research Articles

Quantifying the Degree of Binder Availability in Recycled Asphalt Mix Design Using White and Black Rock Mixes

Quantifying recycled asphalt binder availability in recycled asphalt pavement (RAP) mix design is very essential, as the widely adopted 100% RAP binder availability assumption in RAP mix design never holds correct. Depending on the mix production condition, recycled binder stiffness, and virgin binder properties, the degree of binder availability in the mix is always partial. The present study proposes a simple procedure to estimate the degree of recycled binder availability in RAP mix design. In the proposed methodology, the designer needs to compare optimum binder content of bituminous mixes prepared using white rock aggregate gradation and virgin aggregates, along with mixes designed by blending black rock gradation and virgin aggregates blended in proportion to achieve the target white rock gradation. The binder content in the RAP fraction used in the blending exercise was determined using ignition oven method. RAP mix designs were performed for RAP material collected from two different sources, and design was performed for three mixing durations in a laboratory pug mill—60, 120, and 180s. The mixes were prepared with 50% RAP incorporation level. RAP material was conditioned at 110°C for 2 h, whereas virgin aggregates were superheated to 175°C. Using the methodology proposed, RAP binder availability was found to vary between 92.5% and 96.6% for softer RAP material, 75.9% to 91.5% for mixes incorporating stiffer RAP. With increasing mixing time, even though the total active binder content did not change significantly, a mixture performance test quantified the implication of increased RAP binder availability in mixes. A higher degree of binder activation resulted in mixes being rut resistant, while the same mixes exhibited relatively higher cracking susceptibility.

Perceiving moisture damage of asphalt mixes containing RAP using survival analysis based on Kaplan-Meier estimator and Cox proportional hazards model

Moisture induced stress tester (MIST) has been recently developed which aims to simulate stripping due to repeated pore pressure generation. In the current work, asphalt mixes containing recycled asphalt pavement (RAP) (in proportion of 0, 10, 20, 30 and 40% by weight) were subjected to varying stress cycles of MIST (0, 1000, 2000, 3500, 5000, 10,000 cycles) and indirect tensile (IDT) strength test was conducted on such mixes. AC30 was used for control mix whereas AC10 was adopted for RAP mixes. The results of IDT strength tests assisted in computing the failure times and such times were analysed using survival analysis based on Kaplan Meier (KM) estimator and Cox Proportional Hazards (CPH) model. The results indicated that survival analysis can be effectively utilised to analyse the IDT strength test results. It was observed that increasing stress cycles of MIST increase the time to failure whereas RAP is expected to reduce the time to failure. Moreover, KM estimator indicated that RAP reduces the survival of asphalt mixes. Hazard ratio (HR^) computed using CPH model shows a decrease with the increase in RAP proportion. Both MIST tensile strength ratio (M−TSR) and HR^ revealed that RAP leads to an improvement in moisture damage resistivity of asphalt mixes. Hence, HR^ has the potential to be an effective indicator of moisture damage susceptibility of asphalt mixes. Also, “Good” and negative correlation was observed to exist between M−TSR and HR^. The current study is expected to further enhance our understanding regarding moisture induced damage of asphalt mixes and assist in effectively screening good mixes from poor ones.

Effect of MIST conditioning on the air voids and permeability of hot asphalt mixes containing reclaimed asphalt pavement

Traffic traversing on an asphalt pavement leads to the development of hydrodynamic stress. Hence, moisture-induced stress tester (MIST) was developed to simulate the phenomenon. However, MIST has the propensity to affect the air voids (Va ) and permeability (k) characteristics of the conditioned mix. In this study, an attempt has been made to understand the effect of varying stress cycles of MIST on Va and k. Furthermore, due to the advantages associated with recycled asphalt pavement (RAP) mixes, this study also considers RAP in varying proportions of 10%, 20%, 30% and 40% by weight. The results indicate that MIST conditioning affects both Va and k of asphalt mixes. RAP mixes were observed to undergo higher changes in Va and depicted higher k than control mix. It is expected that the results of the current study may prove to be significant in explaining the change in performance parameters due to MIST conditioning.

Effect of Recycled Asphalt Pavement Binder on Rheology of Crumb Rubber–Modified Binder—An Experimental, Analytical, and Analogical Study

Abstract The popularity of recycled asphalt pavement (RAP) is on the rise because of the benefits of sustainability. In an unavoidable scenario wherein crumb rubber–modified binder (CRMB) is adopted as a base binder in RAP mixes, the binder from RAP will blend with CRMB, thereby influencing its rheology and performance at high, intermediate, and low temperature. Hence, in this study, binder extracted from two RAP sources (RAP X and RAP Y) was blended with CRMB at varying proportions of 15, 25, and 40 % by weight. Isochronal temperature sweeps, isothermal frequency sweeps, and bending beam rheometer tests were conducted on the prepared blends. Thereafter, analytical and analogical studies were performed using master curve construction, 2S2P1D, and Huet modelling. The results indicated that RAP from different sources affects the high-, intermediate-, and low-temperature performance of CRMB. Different RAPs were observed to have contrasting effects on high-temperature performance grading. Intermediate-temperature performance based on cross-over temperature (TCROSS-OVER) indicated a compromise because of the inclusion of RAPs. An evaluation of the differences among critical temperatures at low temperature (ΔTc) indicated the degradation of low-temperature performance. Such changes in high-, intermediate-, and low-temperature performances were validated by complex modulus (G*), stiffness (S(t)), and stress relaxation (E(t)) master curves. Finally, the 2S2P1D and Huet model were observed to depict reasonably good fits for the prepared blends. This study concludes that RAPs from different sources have contrasting impact on CRMB and may adversely impact the intermediate- and low-temperature performance.

Laboratory Evaluation of Performance Properties of Asphalt Binders and Mixes Containing a New Rejuvenator

As higher recycled asphalt pavement (RAP) contents are utilized in asphalt mixtures, the mixes will be stiffer and more brittle, thereby losing resistance to various types of cracking. To offset these changes in stiffness and ductility, rejuvenators have been used in asphalt mixes containing high recycled contents to improve their performance properties. The objective of this project was to evaluate the effect of a new rejuvenator, a corn oil-based coproduct, on the performance of high RAP mixes. Three mixes were evaluated in this study: two 50% RAP mixes with and without the rejuvenator and a control virgin mix. Performance grade and frequency sweep tests were conducted to explore the effect of rejuvenator on the performance of the asphalt binder. Moisture damage, dynamic modulus, rutting, and cracking tests were performed to evaluate the effect of rejuvenator on the mix performance. Results of this study indicated that the new rejuvenator was effective in lowering the stiffness of RAP asphalt binder and improving the resistance to cracking and moisture damage of 50% RAP mix without imposing negative rutting effects.

Rheology and mix performance of rejuvenated high RAP field produced hot mix asphalt with a soybean derived rejuvenator

A laboratory study was conducted to determine the optimum dosage of a bio-based rejuvenator, epoxidised methyl soyate (EMS), needed to obtain a mix design containing 30% unfractionated recycled asphalt pavement (RAP) using a neat asphalt binder with performance grade (PG) 58-28S, rated for standard traffic to meet performance criteria for a PG 58-28S. Based on running a comprehensive rheological characterisation using Superpave binder criteria, 3% EMS by weight of the neat binder was needed to obtain a PG 58-28S at proportions of (75.5% neat binder w/ 3% EMS, and 24.5% RAP extracted binder). The 3% EMS is equivalent to 0.126% by weight of the total mix. Through lab verification, the mix design with 0.126% EMS was shown to meet performance criteria for moisture susceptibility/rutting and low temperature cracking. Field produced mix with 0.126% EMS by weight of total mix was also shown to pass the performance criteria as well for the aforementioned properties. However, the field produced control mix with 20% RAP was not shown to pass criteria for low temperature at −18°C, and thus the field produced control mix became rated as a PG 64-22S. In addition, field density was checked for both the control mix and EMS RAP mix, where both sections had pay bonuses of 3.1% and 4%, respectively.

Aggregate gradation effect on the fatigue performance of recycled asphalt mixtures

This paper presents the details of a laboratory study on the evaluation of the fatigue characteristics of asphalt mixtures containing Recycled Asphalt Pavement (RAP) material using controlled stress indirect tensile fatigue test (ITFT). The effect of different aggregate gradations on the fatigue performance of RAP mixes is the main focus of the study as this helps us to identify the proportion of RAP that can be used from fatigue performance consideration. Two dense mixes and three gap graded mixes, both with different percentages of RAP, were investigated. VG 30 viscosity grade virgin binder was used. The fatigue test was conducted at 25°C. Laboratory fatigue life determined under stress controlled mode increased with increase in the RAP content for all the five aggregate gradations. The corresponding ‘Initial strain vs fatigue life’ trends suggest a decrease (for any specific strain level) in the fatigue life with an increase in the RAP content. However, analysis of the fatigue performance of typical pavement sections with different RAP contents do not suggest any significant detrimental effect of increasing the RAP content for pavements with thick bituminous layers. Use of open graded mixes permits the use of larger binder contents and higher RAP contents in the mix. Fatigue lives of RAP mixes are longer for gap graded mixes compared to dense graded mixes. The fatigue lives of RAP mixes are found to correlate very well with fatigue parameters of the virgin-RAP binder blends prepared in suitable proportions.

Estimation of Blending of Rap Binder in a Recycled Asphalt Pavement Mix

Many of the recycled asphalt pavement (RAP) mix design methods assume 100% blending of the RAP binder with virgin binder to estimate the properties of the binder in the RAP mix. However, 100% blending is not practically achieved. Thus, it is essential to have procedures for determination of the degree of blending so that the properties of the blend can be estimated more accurately from the properties of RAP and virgin binders. To achieve this objective, a detailed study is conducted to evaluate the level of interaction between RAP and virgin binders. This study considers two proportions of RAP (20 and 35%) and two viscosity grades of virgin binders (VG10 and VG30). The difference in the qualities of the binders in the RAP and virgin aggregate portions is evaluated in terms of different binder properties such as G*/sinδ, penetration, and softening point. The results show that the grade of virgin binder and RAP content in the hot mix asphalt concrete governs the degree of blending achieved. Based on the results of the study, a simple approach is proposed for estimation of the properties of the combined (blended) binder in the recycled mix.

Evaluation of recycled asphalt pavement using economic, environmental, and energy metrics based on long-term pavement performance sections

Recycled materials have been used in roadway construction for years. Recently, with the advancement of material processing equipment and mix design technologies involving Recycled Asphalt Pavement (RAP), RAP’s use in pavement construction is increasing. RAP’s various desirable properties spur its use in sustainable development. These merits include energy conservation in mix production, cost savings in material consumption, and environmental protection. Although asphalt mix is considered to be recyclable – meaning RAP could be a sustainable material – in-depth studies verifying and quantifying its effectiveness are limited in the literature. Based on real-world data from pavements constructed with 35% RAP and virgin mixes, this study comprehensively evaluates the sustainability of RAP from three different aspects including cost, energy, and environment. The life cycle cost analysis based on RealCost and life cycle assessment based on PaLATE is used to compare RAP and virgin alternatives. The results suggest that using RAP is more economically efficient and environmentally viable than virgin pavement if thin asphalt overlay is involved. The findings of this study support RAP’s use in current pavement rehabilitation practice, which usually involves relatively thin asphalt overlays.

Effect of silica fume on mechanical properties of concrete containing recycled asphalt pavement

This paper presents the results of a study that investigated the improvement of the mechanical properties of coarse and fine recycled asphalt pavement (RAP) produced by adding silica fume (SF) with contents of 5%, 10%, and 15% by total weight of the cement. The coarse and fine natural aggregate (NA) were replaced by RAP with replacement ratio of 20%, 40% and 60% by the total weight of NA. In addition, SF was added to NA concrete mixes as a control for comparison. Twenty eight mixes were produced and tested for compressive, splitting tensile and flexural strength at the age of 28 days. The results show that the mechanical properties decrease with as the content of RAP increases. And the decrease in the compressive strength was more in the fine RAP mixes compared to the coarse RAP mixes, while the decrease in the splitting tensile and flexural strength was almost the same in both mixes. Furthermore, using SF enhances the mechanical properties of RAP mixes where the optimum content of SF was found to be 10%, and the mechanical properties enhancement of coarse RAP were better than fine RAP mixes. Accordingly, the RAP has the potential to be used in the concrete pavements or in other low strength construction applications in order to reduce the negative impact of RAP on the environment and human health.

Investigating the effect of rejuvenators on low-temperature properties of recycled asphalt using impact resonance test

ABSTRACTUse of recycled asphalt pavement (RAP) in highway construction is highly promoted due to recent awareness in sustainable construction practices. The concerns with material brittleness in utilising higher content of RAP are alleviated through addition of rejuvenators to some extent. Inclusion of rejuvenator to the aged binder improves its flexibility and lessens its cracking potential. A study was undertaken to investigate the effectiveness of the impact resonance (IR) testing in determining low-temperature binder properties through mixture testing. To this effect, the presented study consisted of two stages. In stage I, the IR test was conducted on mixes made with different low-temperature grade binders. Stage II consisted of testing pure RAP mixes treated with a rejuvenating agent at different levels using the IR as well as testing blends of recovered RAP binder and rejuvenator and virgin binder using bending beam rheometer (BBR). The IR test was performed at a range of temperatures between and . The results indicate that the IR test can successfully capture the low-temperature properties of binders in virgin mixes as well as RAP mixes incorporating rejuvenator. A very high linear correlation was observed between stiffness from IR testing of the RAP mix and stiffness from BBR testing of the blend of recovered binder and virgin binder and rejuvenator. A good correlation was also observed between phase angle of RAP mixes obtained from IR with the m-value, a relaxation index, from BBR at a range of temperatures for a given rejuvenator content. The results clearly demonstrate the potential of IR to be used for grading and optimisation for the asphalt binder of RAP and rejuvenator content in lieu of the binder recovery method.

Deformation and cracking performance of recycled asphalt paving mixes containing polymer-modified binder

The presented study investigated the effects of Polymer-modified Binder (PMB) on the stiffness, rutting resistance, and cracking resistance of Recycled Asphalt Pavement (RAP) mixes. Mechanical testing was conducted on six asphalt mixes that contained varying proportions of RAP and polymer binder. Test results revealed that the inclusion of RAP causes a notable increase in the stiffness of mixes, particularly with a 30% RAP proportion. Polymer binder was seen to improve the rutting resistance of all mixes, particularly for the mix containing 30% RAP where a large increase in rutting resistance was achieved with the addition of polymer binder. The presence of PMB in conjunction with RAP decreased the reflective cracking resistance of mixes, where at high RAP contents the negative effects of polymers on the cracking performance of mixes were more significant. This study provided useful performance specifications for RAP mixes for the pavement construction industry in New Zealand.

Improving Recycled Asphalt Mix Performance Through Rejuvenation

Developing technologies that provide sustainable solutions for future pavement construction is vital given the ever-increasing demand on the supply of bitumen and good-quality pavement construction materials. Recycled asphalt pavement (RAP) is a technology that presents many advantages in cost and environmental savings. This study investigated the performance of RAP mixes containing rejuvenation additives to determine the effects of those additives on the deformation (rutting) resistance, cracking resistance, and fatigue performance of RAP mixes. Laboratory testing was conducted on 11 RAP mixes that were manufactured with RAP proportions of 15% and 30%, as well as with the addition of different types of rejuvenating agents. Results produced useful performance indicators for the use of rejuvenation additives in RAP. The mixes that had rejuvenation additives preserved the high deformation resistance of RAP mixes, particularly at the higher RAP proportion of 30% when compared with a mix with no RAP, and concurrently the addition of rejuvenators counteracted against overstiffening effects of RAP. The addition of RAP, especially 30% RAP proportion, had poorer fatigue performance than when only 15% RAP was used, but with the use of rejuvenation agents, the fatigue performance of the high RAP mixes improved significantly. Use of a maltene fraction for RAP rejuvenation had marginally better fatigue performance than a chemical rejuvenation agent. The research results provide a valuable understanding of the behavior of RAP mixes and, in particular, the positive performance results that can be gained by using rejuvenation additives.

Use of RAP Stabilized by Hot Mix Recycling Agents in Bituminous Road Construction

The composition of bitumen plays a vital role in deciding durability of bituminous roads. During the aging process, its composition changes with passage of time. Napthene aromatics are converted to polar aromatics and these in turn to asphaltenes those are responsible for brittleness of bitumen in Recycled Asphalt Pavement (RAP). Therefore, restoration of physico-chemical deficiencies of oxidized bitumen by incorporation of appropriate dose of recycling agent is essential for desired performance of pavement. In the present study, RAP samples have been collected and laboratory studies have been carried out to optimize the percentage of usable RAP. Recycling agent has also been used in this study and the dosage of the recycling agent has been found as 10% by the weight of the bitumen present in RAP. The paper describes the comparison of properties of mixture with recycling agents, which has been prepared in laboratory and commercially available on the RAP material, and their performance has been compared with virgin mixes. Various performance tests such as Retained Stability, Indirect Tensile Strength (ITS) and Tensile Strength Ratio (TSR), Resilient Modulus test has been carried out to compare the performance of RAP modified mixes and virgin mixes. This paper presents the results of performance tests carried out on bituminous mixes with RAP and virgin mixes and their result. The laboratory results indicate that the bituminous mixes with RAP and recycling agent provide better performance compared to virgin mixes.

Quantitative evaluation of blending and diffusion in high RAP and RAS mixtures

Due to variable aging of recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS), the concerns arise over old-new binder blending during mixture production and subsequent diffusion process. In this study, a modified staged-extraction method was validated and employed to extract binder in approximately equal layers from retrieved virgin and RAP/RAS aggregates after mixing and subsequent diffusion treatment. Quantitative analysis was done on extracted binders in terms of large molecule size percentage LMS (%) from gel permeation chromatography (GPC). The results indicated that a well-blended binder film coated virgin aggregates from 50% RAP mix, while a non-homogeneous binder film was observed on RAP aggregates. The system of binder blend coating the virgin and RAP aggregates with un-mobilized RAP binder was validated. A possible composite binder system was found coating the virgin aggregates in 10% RAS mix. The diffusion study showed that within the mixture silo storage time, binder diffusion could be accomplished in both warm and hot mixes containing 50% RAP, indicating that binder homogeneity may not be an issue in high RAP mix. The binder diffusion in RAS mix was captured in a very slow rate. It was suggested that binder homogeneity can still be critical for high RAS mix.

Characterizing Compactability of High RAP and Warm Mix Asphalt Mixtures in the Superpave Gyratory Compactor.

Abstract Compactability of asphalt concrete mixtures is critical for successful long-term performance in the field. Laboratory samples are necessary for volumetric analysis and performance testing during the design process, so the ability to quantify compactability during specimen production in the lab would be highly beneficial. While there has been significant work in defining compaction characteristics of asphalt concrete, most of this work has revolved around traditional Hot Mix Asphalt (HMA), and little work has been done with Warm Mix Asphalt (WMA) or high percentage Recycled Asphalt Pavement (RAP) mixtures. This research examined HMA without RAP (HMA Virgin), HMA with 35 % RAP (HMA RAP), and two WMA technologies with 35 % RAP (WMA 1 and WMA 2). Four compactability metrics were evaluated, including number of gyrations to 92 % density (N92), Construction Densification Index (CDI), the Construction Force Index (CFI), and the newly introduced Normalized Shear Index (NSI). This research found that the WMA technologies improved the compactability of asphalt concrete, as did the addition of RAP. In general, the WMA 1 showed better compactability than WMA 2, but this could be partially attributed to a softer binder grade, higher asphalt binder content, and the potential for a tender mix, as indicated by the normalized shear curve. The HMA RAP mixture also had a higher asphalt binder content compared to HMA Virgin, which could have contributed to the improved compactability. The NSI metric consistently showed the lowest Coefficient of Variation (COV) values and has the potential to distinguish tender mixtures.

Virginia's Higher Specification for Reclaimed Asphalt Pavement

In 2007 the Virginia Department of Transportation (VDOT) decided to allow higher percentages–-more than 20%–-of recycled asphalt pavement (RAP) in hot-mix asphalt with no change in binder grade. For selected VDOT resurfacing projects in 2007, six contractors produced a total of 129,277 tons of mix containing 21% to 30% RAP from seven asphalt plants in four districts. This study estimated the effect of increased RAP percentages on performance and relative cost. Mixes from most of the high-RAP jobs were sampled and tested, as were mixes from roughly comparable jobs containing less than 20% RAP. Laboratory tests revealed no significant difference between the higher RAP mixes and the control mixes for fatigue, rutting, and susceptibility to moisture. Recovered binder was graded to determine the effect of adding higher percentages of RAP. No construction problems were attributed to the use of the mix with the higher RAP percentage. Slight price adjustments were applied to two of the 10 high-RAP projects, but these were not because of the higher RAP percentage. Price and quantity data from all contracts in the 2007 resurfacing schedule were subjected to statistical analysis. The specification allowing higher RAP percentages was found to have a small, statistically insignificant impact on the bid prices for surface mix items. Value engineering proposals received for jobs not advertised with the high-RAP specification showed that the use of more than 20% RAP could reduce costs in at least some cases.

Characteristics of Cold Processed Asphalt Millings and Cement-Emulsion Mix

A study was conducted to characterize the behavior of cold recycled asphalt pavement (RAP) millings rejuvenated with high float emulsion and portland cement, producing a cement-emulsion mix. The main objectives were to investigate how the behavior of RAP mixes was affected by the addition of cement and to find the optimum emulsion and cement contents. Test samples were prepared with four different cement contents, three emulsion contents, and one free water content. It was concluded that Hveem stability values increased with cement content but decreased with emulsion content. The addition of portland cement affected the Hveem stability value of samples cured under soaked conditions more than those cured under dry conditions. Samples prepared with 2 percent emulsion had the highest gain in soaked stability because of the addition of cement. Overall it was concluded that a cold RAP mix containing a low percentage of cement would perform better than conventional cold RAP mixes.