Recycled Asphalt Pavement Binder Research Articles

Influence of Recycled Asphalt Pavement on Interfacial Energy and Bond Strength of Asphalt Binder for Different Types of Aggregates

The bond between aggregate and asphalt binder depends on many factors, such as chemistry of materials, nature of aggregates, and quality of asphalt binder. The present study evaluates the effects of recycled asphalt pavement (RAP) on the bonding behavior of asphalt binder for acidic (granite and quartzite) and basic (basalt and limestone) aggregates. AC30 binder was blended with different proportions of RAP binder (15%, 25%, and 40%). The interfacial energy and bond strength of 16 combinations (four asphalt binders × four aggregates) of aggregate-asphalt binder system were evaluated based on a surface free energy (SFE) approach and binder bond strength (BBS) test, respectively. One of the strong motivations of the present study was to evaluate how interfacial energy parameters calculated based on the SFE of an aggregate-asphalt binder system may correlate with the outcome obtained from a BBS test. The results showed that AC30 binder modified with RAP binder had a good performance for basic aggregates compared with acidic aggregates. Basic aggregates (limestone and basalt) showed cohesive failure before and after conditioning, indicating minimal effects of water on interfacial bond strength. However, acidic aggregates (granite and quartzite) showed cohesive failure in dry conditions and adhesive failure after wet conditioning, implying detrimental effects of water on interfacial bond strength for these aggregates. The failure pattern of aggregates in cohesion was supported by a reduction in cohesion energy of asphalt binder after the addition of RAP binder. Correlation between interfacial energy parameters (obtained from SFE) and BBS strength depends on aggregate types and failure patterns.

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.

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.

Characterizing blending efficiency of plant produced asphalt paving mixtures containing high RAP

The incorporation of high percentage (>30%) recycled asphalt pavement (RAP) into asphalt mixtures has become more popular. Various methods have been proposed to determine how much of RAP binder can be effectively blended into virgin binder. However, few methods can be used to test the blending efficiency of plant-produced asphalt mixtures. This study proposed a method of measuring the blending efficiency of plant-produced mixtures using Fourier Transform Infrared Spectroscopy (FTIR). Three types of asphalt mixtures, including one warm mix, two hot mixes with or without rejuvenator, were used to validate the proposed method. Results indicate that RAP particles varied in oxidation, but mixing RAP binder with virgin binder could reduce this heterogeneity. Among the three mixtures, warm mix showed the highest blending efficiency, while adding rejuvenator had a limited effect on the blending efficiency. The proposed method was further verified using Gel Permeation Chromatography (GPC).

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.

Modeling of the Rheological Properties of Asphalt Binder and Asphalt Mortar Containing Recycled Asphalt Material

The use of recycled materials in asphalt pavements increased significantly over the years, determining well known environmental and economic benefits. Many research agencies and road authorities evaluated the impact of Recycled Asphalt Pavement (RAP) on pavement performance. Nevertheless, the mechanism governing the interaction between virgin asphalt binder and aged RAP binder is not well understood. In this paper, the effect of RAP on the rheological properties of asphalt binders and mortars is experimentally evaluated, and theoretically modeled with the objective of defining a relationship between the linear viscoelastic (LVE) properties of binders and those of the corresponding mortars. Three asphalt binder types, obtained by blending a hard and a soft binder at three different percentages, were mixed with three different contents of a Selected fraction of Recycled Asphalt Pavement, called SRAP, for preparing the asphalt mortar samples. Dynamic Shear Rheomether tests were performed on binders and mortars to determining the complex modulus over a wide range of temperatures and frequencies. The rheological properties of the compound of virgin and RAP binder were evaluated by using a new approach based on a modified version of the Nielsen model, avoiding the extraction and recovery method. The results were then modelled by using the analogical 2S2P1D model, consisting of one spring, two parabolic and one-dashpot elements combined in series and then assembled together with a second spring in parallel. Based on test results, a simple experimental relationship between the characteristic times of the binder and the percentage of RAP in the mortar was found.

Rheological modeling of asphalt binder and asphalt mortar containing recycled asphalt material

The use of recycled materials in asphalt pavements has increased significantly over the years, with well-known environmental and economic benefits. However, the mechanism governing the interaction between the virgin asphalt binder and the aged binder contained in recycled asphalt pavement (RAP) is not entirely understood. In this paper, the effect of RAP on the rheological properties of asphalt binders and mortars was experimentally investigated and modeled with the objective of defining a relationship between the linear viscoelastic properties of binders and those of the corresponding mortars. First dynamic shear rheometer tests were performed on binders and mortars, prepared with a selected fraction of RAP, for measuring the complex modulus over a wide range of temperatures and frequencies. Then, the effective rheological properties of the combined virgin and RAP binder in the mortar were evaluated with a new approach based on a modified version of the Nielsen model, avoiding extraction and recovery. Finally, the material response was modeled using the analogical 2S2P1D model, consisting of one spring, two parabolic and one-dashpot elements combined in series and then assembled together with a second spring in parallel. A significant stiffening effect due to RAP was observed both on asphalt mortar complex modulus and on the corresponding asphalt binder parameter back-calculated with the modified Nielsen model. At the end, binder and mortar characteristic time, which is one of the 2S2P1D model parameter, was linked to the recycled material content through a simple exponential expression experimentally derived.

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.

Quantitative Characterization of Binder Blending

The current tendency in the asphalt paving industry is to increase the use of recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS). However, a major concern that limits the use of RAP or RAS is the uncertainty about how much of the aged binder in RAP or RAS can be blended into virgin binder. Studies have focused on the diffusion between old and new binders. However, little research has been conducted to determine how much recycled binder could be mobilized and made available to coat aggregates. This study developed a laboratory procedure to quantify the rate at which aged binder was mobilized for recycled mixtures containing up to 80% RAP and 10% RAS. A new term, “large molecular size percentage (LMSP),” was derived from gel permeation chromatography testing and used to characterize recycled and virgin binders as well as their blends. Blending charts were generated for virgin–aged binder blends containing 0% to 100% RAP or RAS binder in LMSP. The relationship was found to be linear between LMSP and RAP or RAS binder content. An experiment was conducted to validate the method proposed for determining the mobilization rate. The results showed that the RAP binder mobilization rate decreased with the increase in RAP percentage in the mixture, which could be close to 100% at low RAP contents (10% and 20%); the rate dropped from 73% to 24% when the RAP percentage increased from 30% to 80%. For RAS, the mobilization rate reached a peak at 5% RAS content and then started to decrease with the increase in RAS content.

Strategies for Incorporating Higher Recycled Asphalt Pavement Percentages

Because there is a greater emphasis on promoting sustainable materials within transportation infrastructure, state agencies in the U.S. Northeast are investigating different strategies that will enable the use of higher percentages of recycled asphalt pavement (RAP) while not sacrificing the performance of the asphalt pavement. In particular, most state agencies in the Northeast are concerned with the fatigue and thermal cracking performance, as well as the general workability and handling of the higher-RAP-content asphalt mixtures when greater percentages are used. In conjunction with the Transportation Pooled Fund study TPF 5(230), Evaluation of Plant-Produced High-Percentage RAP Mixtures in the Northeast, three potential strategies were evaluated for incorporating higher RAP contents: using a softer asphalt binder grade to offset the stiff RAP asphalt binder, limiting the amount of RAP binder credited to the total asphalt content of the asphalt mixture, and using a performance-based specification that the high-RAP content mixture must meet for acceptance. The findings of the strategies through plant-produced mixtures, as well as case studies evaluated in detail through laboratory test procedures and analysis, are summarized. The project trials and results shown will, it is hoped, provide guidance to other agencies looking to increase the percentage of RAP used in their asphalt mixtures.

Stiffness of High-RAP Asphalt Mixtures: Virginia’s Experience

In the year 2006, the price of asphalt binders in the United States increased by almost 50% over the 2005 prices. The use of higher recycled asphalt pavement (RAP) percentages with locally available binders was adopted as an approach to reduce the demand on specialty more expensive virgin binder and virgin aggregates in Virginia. The purpose of this study was to investigate concerns that the performance of these higher RAP mixtures could be compromised because of excessive mixture stiffening due to the aged RAP binder. The results indicated that measured binder stiffnesses of high-RAP mixtures are not significantly affected by RAP amount, high temperature true grade of high-RAP mixtures averaged only approximately 2.0°C above that of base virgin binder, and that the correlation between binder stiffness and flow number for the selected high-RAP mixtures considered was good. The study concludes that the addition of higher amounts of RAP to asphalt-concrete mixtures currently produced in Virginia has not resulted in excessively stiffened mixtures as previously thought; the stiffnesses of high-RAP mixtures are primarily governed by the virgin binder stiffness.

The properties of asphalt binder blended with variable quantities of recycled asphalt using short term and long term aging simulations

The objective of this paper is to characterize the rheological properties of asphalt binders blended with various amounts of asphalt extracted from a recycled asphalt pavement (RAP) mixture. Three asphalt binder aging states were simulated and evaluated: unaged, rolling thin film oven (RTFO) aged, and pressure aging vessel (PAV) aged. A Superpave PG 58-28 binder was applied as control binder and another four RAP binder percentages were studied in this research, 30%, 50%, 70% and 100%. Rotational viscosity testing was conducted with a Brookfield viscometer. Temperature and frequency sweep tests were conducted using a dynamic shear rheometer. Master curves were constructed based on the dynamic shear moduli ( G ∗). The results showed that there are significant differences in dynamic shear moduli ( G ∗) master curve performance for high percentage RAP binder blends versus virgin binders at the three aging states. Increasing RAP concentration and further aging conditions contribute to the increased stiffness and viscosity of RAP binder blends.