Reclaimed Asphalt Pavement Content Research Articles

Evaluation of rutting resistance and moisture susceptibility of high RAP content asphalt mixtures containing bio-based rejuvenators

Hot Mix Asphalt (HMA) incorporating high Reclaimed Asphalt Pavement (RAP) contents can potentially have good rutting resistance due to the higher stiffness of the aged RAP-binder. The use of rejuvenators to enhance the workability and performance of high RAP mixes is becoming a common practice. However, the impact of rejuvenators on the rutting resistance and moisture susceptibility of high RAP mixes has not been studied exhaustively. The Hamburg Wheel-Tracking (HWT) test was used in this study to evaluate the asphalt mixture performance in terms of their resistance to permanent deformation and moisture damage at two conditioning temperatures of 44℃ and 50℃. Highly recycled asphalt mixes containing 50% RAP were prepared with various bio-based rejuvenators and a soft binder to compare with a control mix with 20% RAP content. Different HWT data analysis methods were used to quantify the mix performance. The results indicated that the rejuvenated high RAP mixes showed increased rut depth and higher possibilities of stripping compared to the control mix and the 50% RAP mix without rejuvenators. Regardless of the rejuvenator type and dosage, both the control and the rejuvenated high RAP mixes experienced severe stripping due to the increase in testing temperature. The 50% RAP mix performed best at both test temperatures. Therefore, caution is warranted concerning the adverse effects of rejuvenators or soft binders on the rutting performance and moisture susceptibility of high RAP mixes. Furthermore, traditional HWT parameters could be misleading due to the confounding effects of post-compaction and moisture-induced deformation. Parameters developed by the novel HWT data analysis methods could separately evaluate the rutting resistance and moisture susceptibility.

Investigation on the influence of conditioning time on the performance of hot-recycled mixture under ambient temperature

Hot-recycled asphalt mixture (HRAM) has gained more attention due to its favorable performance and reuse of reclaimed asphalt pavement (RAP). However, involvement of the blending between virgin and aged asphalt may require more time to reach stability after the mixing process. It has been generally agreed that the change in degree of blending (DoB) between virgin and aged asphalt influences the performance of HRAM. Hence, it is of vital importance to reveal the development of the performances of HRAM in primary period and offer a reasonable conditioning time before conducting laboratory test to avoid over- or under-estimation. As many factors, including RAP content, aging degree of RAP and mixing procedure, may influence the conditioning time of HRAM, in this research, the HRAM with different RAP contents is taken into account. Specimens are stored at ambient environment (around 25 °C) for different days. Then, macroscopic performance tests evaluating high- and low-temperature performances as well as mechanical properties are conducted. Meanwhile, atomic force microscopy (AFM) is applied to quantify the change of nanoscale properties of HRAM under different conditioning time. The result shows that the macroscopic performances change significantly with conditioning time. But HRAM with different RAP contents exhibits distinct developing trend. Nevertheless, test results within 4 days varies significantly among all. AFM test reveals that DMT modulus increases with conditioning time, which is the reason for the performance change. Considering the time cost in laboratory testing, it is recommended for HRAM specimen to be conditioned at ambient temperature for at least 4 days before the tests. 7-day conditioning is better for HRAM with higher RAP content if time permits.

Evaluation of the impact of long-term aging on fracture properties of warm mix asphalt (WMA) with high RAP contents

This study aimed to investigate the effects of long-term aging on the fracture characteristics of Warm Mix Asphalt (WMA) containing Reclaimed Asphalt Pavement (RAP). To this end, various RAP contents (0, 50, 75, and 100%) and one WMA additive (Zycotherm) were used. The Semi-Circular Bending (SCB) fracture test was conducted at intermediate temperature and fracture parameters, including the fracture force, fracture toughness, strain energy, J-integral, stiffness, and flexibility index were measured to identify the impact of aging and RAP addition on different fracture properties of WMA mixtures. To remedy the problem concerning the amorphous trend of fracture properties over the service time and intersecting the curves of fracture parameters versus service time, the area beneath the fracture parameter was employed as a reliable index for comparing different mixes. Then, summations of the area of all fracture parameters versus service time for various mixtures with different RAP content were identified as the overall fracture resistance of each mixture. Finally, an analysis of variance (ANOVA) was determined to statistically assess the results of the SCB fracture test. This study highlights the importance of considering long-term aging effects on WMA mixtures containing RAP and the potential benefits of using high RAP content in flexible pavements. Overall, this research can help agencies make a more precise decision regarding the consequences of high RAP content on the long-term performance of asphalt pavements.

Evaluation of thermal cracking probability for asphalt concretes with high percentage of RAP

The paper presents determination of the probability of thermal cracking of asphalt mixtures with different reclaimed asphalt pavement (RAP) content on the basis of laboratory tests and analytical evaluation using thermal stress development method. Probability was evaluated taking into consideration: the type and gradation of the mixture and the quality and content of RAP. Thermal stresses were determined using two models: elastic and viscoelastic. Addition of RAP decreases the low-temperature properties of all the tested asphalt mixtures. In the case of wearing and binder courses, addition of 20% of RAP increases the cracking temperature by around 5–6 °C.

Investigation on Fracture Performance of Hot-Mix Asphalt with Reclaimed Asphalt Pavement under Fatigue Loading

Reclaimed asphalt pavement (RAP) has been widely used in asphalt pavement. However, the fatigue performance of hot-mix asphalt (HMA) with RAP is a critical factor to ensure durability. In this study, fatigue tests using an Overlay Tester (OT) were conducted using a novel load-controlled mode. RAP contents were 0, 25% and 50%, respectively. In the cyclic loading, fatigue life and energy parameters were measured. Results indicated that RAP decreased both the fracture energy and tensile strength. Fatigue life was determined using two methods. RAP was proved to be beneficial in prolonging the fatigue life using the two methods at 25 °C. However, opposite conclusions were made about the effect of RAP on fatigue life at −10 °C. At −10 °C, compared to HMA without RAP, the cumulative dissipated energies decreased by 49.1% and 77.3% when RAP contents were 25% and 50%, respectively. At 25 °C, compared to HMA without RAP, the inclusion of 25% RAP increased the cumulative energy by 31.1%, while 50% RAP decreased the cumulative energy by 41.2%. The developments of the dissipated energy and the cumulative energy were consistent with the fatigue life results determined by the first method.

Field Performance Evaluation of Base Course Constructed with Reclaimed Asphalt Pavement and Virgin Aggregate Blends

Abstract This study presents the results of four years of data collection from a test site that is constructed as part of an actual roadway. The focus of the study was to evaluate the possibility of achieving similar or better performance characteristics from base course sections constructed with reclaimed asphalt pavement (RAP) blends compared to sections with 100 % virgin aggregate (VA). Two base course sections were constructed by blending VA with 20 % RAP and two with 30 % RAP (four RAP-VA sections). Blends were achieved using fine processed RAP with two different average binder contents (4.9 and 5.6 %). Additionally, two sections were constructed with 100 % VA for comparison. During construction, strain gauges were embedded into the asphalt and base course layers. Long-term performance evaluations were monitored based on data from the strain gauges and in situ testing. Falling weight deflectometer and light weight deflectometer tests were used to evaluate modulus values, and the results showed that all sections constructed with RAP-VA blends had equal or greater modulus values than the 100 % VA sections. International roughness index tests coupled with data from strain gauges were used to evaluate deformations. The results showed that three of the four RAP sections had deformations close to or less than 100 % VA sections (desired outcome). The only exception was in the section constructed with 30 % RAP with lower binder content (4.9 %). Findings from this study showed that field evaluations require multiple methods of testing, and modulus-based measurements alone should not be relied on for performance evaluations. This study demonstrated that it is possible to design base course sections with RAP that perform similar to or better than 100 % VA. A proper blend requires the gradation and binder content of RAP to be characterized and the percentage of RAP blended with VA to be determined based on these properties.

Experimental Study of Permeable Asphalt Mixture Containing Reclaimed Asphalt Pavement

The current focus of research attention on reclaimed asphalt pavement (RAP) utilization is expanding the applications of RAP. This study aims to analyze the road performance of recycled permeable asphalt mixtures (RPAMs), which represents a novel direction for utilizing RAP. Firstly, the Marshall design method was used to carry out the material composition design of the RPAM with varying RAP contents (10%, 20%, and 30%). Subsequently, the performance of the RPAM with different RAP contents (10%, 20%, and 30%) and preheating temperatures (120 °C, 130 °C, 140 °C, 150 °C, and 160 °C) was tested with a permeable asphalt mixture containing 12% high-viscosity asphalt as the control group. The mixture’s performance included high-temperature stability, low-temperature crack resistance, water stability, anti-raveling performance, and dynamic mechanical properties. The results indicate that the higher the RAP content, the better the high-temperature performance of the RPAM, while the low-temperature performance, water stability, and anti-raveling performance deteriorate. At 30% RAP content, its pavement performance is comparable to that of the control group mixture. However, increasing RAP preheating temperature can improve low-temperature and water stability but may reduce high-temperature performance. The optimal RAP preheating temperature for pavement performance is between 140 and 150 °C. The dynamic modulus test showed that the higher the RAP content, the greater the dynamic modulus of the RPAM, leading to better high-temperature stability but reduced low-temperature crack resistance. The influence of RAP preheating temperature is the opposite. These test results demonstrate the feasibility of utilizing RAP for paving permeable asphalt pavement under controlled RAP content and preheating temperature conditions.

Study the Effect of using RAP in Warm Mix Asphalt Pavement.

Sustainability is providing the needs without compromising the ability of the strategical forming to meet their requirements. The production of warm asphalt mixtures using recycled pavements produces economic and environmentally friendly mixtures, which is the most important advantage of this work. This research aims to determine the effect of recycled asphalt concrete (RAP) on the indirect tensile strength of warm asphalt mixtures and Marshall Properties. Models of warm asphalt mixtures using Aggregate from the Al-Nibaay quarry, Asphalt with a degree of penetration (40-50) from the refinery of the cycle, and obtained Recycled asphalt concrete from Salah Al-Din Road, Al-Ameriya area in Baghdad are prepared. Use five ratios of (0, 10, 20, 30, and 40%) of recycled asphalt concrete. Marshall Design method is adopted to estimate the perfect existence of the asphalt cement for sample preparation. The mixtures properties, volumetric properties, and indirect tensile strength test are evaluated to assess bonding strength. Results show that the increase in the replacement percentage of RAP causes an increase in flow and air void and decreases the bulk density, voids in mineral aggregate (VMA), and voids filled with Asphalt (VFA). Stability increases with increased RAP content until it reaches its peak and falls. The highest stability value is at 30% RAP by 58%, about the indirect tensile strength test. The increase in the RAP ratio increases the tensile strength and the bonding between the components. So including RAP material in warm asphalt mixtures improves properties and meets performance requirements.

Numerical simulation of effect of reclaimed asphalt pavement on damage evolution behavior of self-compacting concrete under compressive loading

The preparation of self-compacting concrete (SCC) using reclaimed asphalt pavement (RAP) to replace part of natural coarse aggregate can realize efficient recycling of resources and have achieved good economic benefits. However, the mechanism of the effect of RAP on the mechanical properties of concrete is still not clear. Therefore, a discrete element model (DEM) of SCC with different RAP contents is established. The bonding characteristics between RAP and cement paste were considered and the crushable aggregate was generated to improve the model reliability. Based on the DEM, the influence of RAP on mechanical behavior and failure mode of SCC under uniaxial compression load was analyzed. The results indicated that RAP significantly affects the total number and growth character of microcracks. The microcracks appear earlier and the total crack number decreases with RAP content ranging from 0% to 100%. Cracks are more curved and formed network damage with RAP content increase. Furthermore, the simulation result shows that RAP affects concrete's crack type under compression load. This study helps to understand effects of RAP on the damage evolution behavior of SCC and the related mechanism.

Cracking resistance evaluation of epoxy asphalt mixtures with 100% reclaimed asphalt pavement (RAP)

Despite the recycling of reclaimed asphalt pavement (RAP) providing great economic and environmental benefits, conventional technologies exhibit poor cracking resistance and cannot achieve high RAP content. The major objective of this paper is to evaluate the cracking resistance of recycled mixtures containing 100% RAP using epoxy asphalt, and to determine an optimal production method. In this paper, the effects of temperatures, epoxy proportions, and gradations on cracking resistance of epoxy-recycled mixtures with 100% RAP were explored through semi-circular bending (SCB) tests, and the mechanism was explained by laser scanning confocal microscopy (LSCM) tests. Subsequently, the validity of SCB parameters was examined using statistical analysis, and a new index (Cracking Resistance Comprehensive Score, CRCS) for evaluating the cracking resistance of epoxy-recycled mixtures was proposed through principal component analysis (PCA). The results indicate that the graded mixture with an epoxy proportion of 30% could be the best solution to recycle 100% RAP, which can restore the cracking resistance to the level of virgin mixtures, outperforming the conventional recycling technique. Statistical analysis shows that temperatures and epoxy proportions have significant effects on SCB parameters, and the fracture energy until failure (Gf1) or crack resistance index (CRI) is valid for characterizing the cracking behavior of epoxy asphalt mixtures. Moreover, CRCS contains over 90% of the original information and effectively identifies the effects of temperatures, epoxy proportions, and gradations, which can be applied to evaluate and rank the cracking resistance of epoxy-recycled mixtures.

Laboratory evaluation of the performance of reclaimed asphalt mixed with composite crumb rubber-modified asphalt: reconciling relatively high content of RAP and virgin asphalt

ABSTRACT Reclaimed asphalt pavement (RAP) applications are largely limited by the insufficient performance of reclaimed asphalt (RA). To address this challenge, the composite crumb rubber-modified asphalt (CCRMA) with SBS and SBR modifiers was mixed with RA to prepare reconciling and reclaimed modified asphalt (RRMA) and evaluate its performance in laboratory tests. Experimental groups of RRMA included five RA contents (30%, 40%, 50%, 60%, and 70%) and three aging degrees. Results showed that RRMA’s high-temperature and fatigue resistance performances improved by adding CCRMA, while this improvement was weakened with increasing RA content and aging degree. This was because the addition of CCRMA reduced the morphology of ‘bee-like structures’ and improved resistance to deformation. CCRMA slightly reduced moderate-temperature crack resistance but still improved low-temperature crack resistance because adding CCRMA reduced the internal adhesion of asphalt. The moderate-temperature crack resistance was below the threshold. However, it is necessary to consider adding other technical means when RRMA was aged for more than 20 hours with more than 60% RA content. Furthermore, the reliability of excellent performance was 85% for RRMA with 30% RA content under a short-term aging state, which provided a reference for the design of reclaimed asphalt binder.

Use of the Iron Chloride Type of Lewis Acid Catalyst in High Reclaimed Asphalt Pavement Content Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) as a partial replacement for virgin aggregates and asphalt binders has received considerable attention recently. This approach is one of many promising methods for improving sustainability. However, many state Departments of Transportation are cautious in adopting high RAP content into their designs because of cracking and durability issues resulting from the aged RAP binder. A Lewis acid catalyst has been used to modify the asphalt binder’s chemical composition and disrupt the associated molecules formed in the aged RAP binder. The objective of this study is to assess the effectiveness of the use of a Lewis acid catalyst in improving the cracking resistance of an asphalt mixture containing high RAP contents. A suite of laboratory mechanical tests was performed, namely, the dynamic modulus test for linear viscoelastic properties; the semi-circular bend, Illinois flexible index, ideal cracking tolerance, and simplified viscoelastic continuum damage tests for fracture and fatigue resistance; the loaded wheel tracking test for rutting resistance and moisture susceptibility; indirect tensile creep compliance and strength tests for low-temperature cracking resistance; and the Cantabro abrasion test for durability. Further, AASHTOWare Pavement ME software was used to predict the long-term performance of asphalt pavements containing mixtures with high RAP contents and a Lewis acid catalyst. Results showed that the use of the Lewis acid catalyst can disrupt associated molecules formed in the aged RAP binder. Thus, asphalt mixtures containing high RAP contents (recycled binder ratio > 0.20) and a Lewis acid catalyst exhibited similar performances to conventional mixtures. Further, Pavement ME predicted fatigue cracking was lower for a structure containing a FeCl3-modified mixture as compared to a similar one with no FeCl3, illustrating the effectiveness of FeCl3.

Effects of Coarse Aggregate Rap Content on the Mechanical and Shear Performance of HMA by the UPT Method

Abstract In recent years, the use of materials derived from recycled asphalt has attracted the attention of airfield and highway construction researchers. Since the making of these products is economically cost-effective, one idea about how to use them is to use coarse-grained crumbs from recycled Asphalt Pavement (RAP), which are agglomerates that can be found in coarse RAP, as a replacement for virgin asphalt.The goal of the current study is to investigate the performance of hot mix asphalt created with various percents of RAP. The punching shear strength of cylindrical specimens versus the penetration of steel rods with fixed and determined diameters into an asphalt specimen is one of the tests used to study the shear strength of asphalt. Other typical tests include a test of the structural strength and resilient modulus with two rectangular and sinusoidal loading shapes, respectively, as well as the specimen's strength against different temperatures of asphalt mixtures containing 10, 20, and 30% coarse-grained RAP. The results show that the resilient strength of the samples with a maximum 30% coarse-grained RAP is within reasonable limits. Furthermore, the semi-sinusoidal loading has a higher resilience modulus than rectangular loading. It is also observed during uniaxial penetration testing (UPT) that increasing the RAP increases the penetration of the steel rod, thereby implying that the shear strength of the asphalt has decreased.

Fatigue of Cold Recycled Cement-Treated Pavement Layers: Experimental and Modeling Study

Fatigue is the main design criterion for cold recycled cement-treated mixtures (CRCTMs). However, the literature shows that the fatigue behavior of such mixtures is still not well known. For example, the effect of increasing reclaimed asphalt pavement (RAP) contents is yet a topic of discussion. This experimental and modeling study helps fill knowledge gaps on CRCTM fatigue behavior using long-term curing fatigue tests and three design methods currently being used in different countries. The objectives of this study were: (1) to characterize the mechanical and fatigue behavior of mixtures of RAP, aggregates and cement; (2) to evaluate the fatigue life of pavements with base and subbase layers of such mixtures using the novel Brazilian design method (MeDiNa); and (3) to compare the results with those obtained using the South African Pavement Engineering Manual (SAPEM) transfer functions and the American Association of State Highway and Transportation Officials AASHTOWare Pavement Mechanistic-Empirical Design (PMED) software. The mixtures were tested in the laboratory using flexural static and cyclic tests, and the required parameters to use the methods were obtained. Experimental results and modeling demonstrated a superior fatigue behavior of recycled layers with higher RAP contents. On the other side, layers with lower RAP contents abruptly lost stiffness in short periods, making thicker structures necessary. Therefore, using high RAP contents is not only a sustainable practice, but also a technical benefit. The equivalent single axle loads obtained using the SAPEM were higher than those obtained using MeDiNa, while the PMED ones were higher than both previous methods. Despite the inherent differences, this suggests that MeDiNa is more conservative. It also highlights the importance of calibration based on long-term pavement performance data.

Mitigation Strategy Selection for Asphalt Mixtures with High Reclaimed Asphalt Pavement Content

Economics and sustainability goals have driven higher use of recycled asphalt materials (RAMs), such as reclaimed asphalt pavement (RAP) and recycled asphalt shingles, in the pavement industry. Owing to the brittle nature of aged binders found in RAMs, a mitigation strategy is usually needed to ensure adequate cracking performance. Determining a proper mitigation strategy is vital to designing long-lasting asphalt concrete (AC) pavements with balanced performance. This study explored the use of mitigation strategies on AC mixtures with intermediate and high RAP contents, using materials from four mixtures that were part of a mill and overlay project in Milford, Delaware. This project included one standard mixture and three experimental mixtures with 25%–40% RAP. This paper presents performance data for field cores, plant-mixed laboratory-compacted specimens, and laboratory-mixed laboratory-compacted specimens. The effects and benefits of using a softer binder versus a recycling agent and the effects of using both a softer binder and a recycling agent to mitigate the stiff RAP binder are explored. To understand the effects of each mitigation strategy with aging, data from one-year field-aged cores and from laboratory-aged specimens are shown. Adjusting only one variable to mitigate the increased stiffness and brittleness of recycled binders yielded the best results in this study. Additionally, some test parameters were found to be sensitive to aging, including the flexibility index from the semicircular bend test and the cracking test (CT) index from the IDEAL-CT, while others were not observed to be sensitive to aging, including the fracture energy measured by the low-temperature disk-shaped compact tension test.

Analysis of Reclaimed Asphalt Pavement with Rejuvenating Materials

Reclaimed asphalt pavement (RAP) is currently commonly used in road construction. Reclaimed asphalt pavement can enhance environmental sustainability while also reducing reclaimed pavement disposal issues. In this study, waste cooking oil (WCO) was utilized as rejuvenating material. There are different samples, where Sample A is the control mixture which is virgin mixture without rejuvenator contain 0% of RAP content. Sample B is the rejuvenated RAP mixtures including 25% and 50% of RAP content combined with WCO, while sample C is the non-rejuvenated RAP mixture containing 25% and 50% of RAP content. In addition, sample D is for 100% RAP content. Therefore, to evaluate the engineering properties, different experimental test, including Marshall stability and flow, dynamic creep modulus and indirect tensile strength are applied, and the optimum percentage was determined based on the result. The findings revealed that reclaimed asphalt pavement with rejuvenating materials enhanced the performance of stability and deformation resistance. Moreover, the indirect tensile strength increases with the increase of RAP content. Based on the findings, it can conclude that 100% of reclaimed asphalt pavement showed the optimum value and significantly enhanced the performance of reclaimed asphalt pavement with rejuvenating materials by reducing pollution.

Rheological Characterization of Reclaimed Asphalt Binder Blended with The Neat And Sbs-pma Binders

Reusing reclaimed asphalt pavement material guarantees a substantial optimization of non-renewable material resources, emissions reduction, and decreasing landfill space, along with the economic benefits associated with saving the costs of purchasing and transporting new aggregate and asphalt binder for asphalt concrete mixture production. This study aims to investigate the influence of aged asphalt binder from reclaimed asphalt pavement on the virgin asphalt binder’s rheological properties. Therefore, different dosages of RAP binder (20%, 30%, and 40% by weight of the total mix) were blended with neat asphalt binder (40-50), penetration grade (P40), and SBS polymer asphalt (SBS-PMA) binder. Using both traditional and Superpave performance testing methods, the effects of RAP on the blend's consistency, viscosity, softening, elastic recovery, rutting (permanent deformation), fatigue cracking, and low temperature cracking were evaluated. The results revealed that the RAP binder decreased the penetration value of both neat and SBS-PMA binders. The neat asphalt binder’s viscosity and softening point increased with the increase in RAP content, whereas they decreased for SBS-PMA. The RAP binder decreases the SBS-PMA elastic recovery. where the neat asphalt experienced a little improvement in elastic recovery when blended with the RAP binder. The Superpave test results revealed that the RAP binder deteriorates the performance of the SBS-PMA binder at high, intermediate, and low testing temperatures. With the addition of 20%, 30%, and 40% RAP, the high-temperature PG grade of SBS-PMA blends decreased by 0.64%, 0.95%, and 1.10%, respectively, while the low-temperature PG grade increased by 23%, 31%, and 32%, respectively. In contrast, the RAP improves the neat asphalt blend's high-temperature performance grade and deteriorates intermediate and low-temperature performance grades. The addition of 20%, 30%, and 40% RAP increased the neat asphalt blends' high-temperature properties by 1.5%, 3.3%, and 4.5%, respectively. whereas the neat asphalt low-temperature PG grade increased by 5%, 11%, and 15% with the addition of 20%, 30%, and 40% RAP, respectively. In summary, the performance of virgin and RAP binder blends depends on the individual characteristics of the blended asphalt binders

Effects of Asphalt Mixture Constituents on the Recycled Binder Contribution

Reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) are incorporated into some asphalt mixtures produced today. The use of recycled asphalt materials (RAM) in asphalt mixtures encompasses engineering challenges pertaining to uncertainty in the proportion of the recycled binder that is in contact with and blends with the virgin binder in the asphalt mixture, termed recycled binder contribution (RBC) here. Recent research shows that agglomerations of RAM particles are the main cause of partial RBC. These agglomerations prevent recycled binder from interacting with the virgin binder. However, current practices generally assume complete RBC and a detailed understanding of the role of asphalt mixture constituents on RBC does not at present exist. The use of softer binders, extenders, and recycling agents has been proposed in high-RAM-content mixtures to restore recycled binder stiffness and embrittlement. However, the effects of asphalt binder variables as well as RAM type, source, and content on RBC is at present poorly understood. This paper aims to investigate the effects of asphalt mixture constituents on the RBC in asphalt mixtures using energy-dispersive x-ray spectroscopy (EDS) tracer-based microscopy analysis. It is found that the virgin binder, RAM type, and source significantly influence RBC in asphalt mixtures. However, RAP age level and content as well as additives are found to have only marginal impacts on RBC.

Study on Road Performance of Polyurethane Cold-Recycled Mixture.

To give full play to the advantages of polyurethane as a binder, such as mixing at room temperature, short curing time, and high curing strength, polyurethane was used as the binder of a waste asphalt mixture, and the pavement performance of PCRM (Polyurethane Cold-Recycled Mixture) was analyzed. Firstly, the adhesion performance of polyurethane binder with new and old aggregates was evaluated using the adhesion test. Then, the mix proportion was designed according to the material characteristics, and the reasonable molding process, maintenance conditions, design indexes, and the optimal binder ratio were proposed. Secondly, the high-temperature stability, low-temperature crack resistance, water stability, and compressive resilient modulus of the mixture were evaluated through laboratory tests. Finally, the pore structure and microscopic morphology of polyurethane cold-recycled mixture were analyzed by industrial CT (Computerized Tomography) scanning, and the failure mechanism of polyurethane cold-recycled mixture was revealed. The test results show that the adhesion between polyurethane and RAP (Reclaimed Asphalt Pavement) is good, and the splitting strength of the mixture increases greatly when the ratio of glue to stone reaches 9%. Polyurethane binder has low sensitivity to temperature and poor water stability. With the increase of RAP content, the high-temperature stability, low-temperature crack resistance, and compressive resilient modulus of PCRM showed a decreasing trend. When the RAP content was less than 40%, the freeze-thaw splitting strength ratio of the mixture was improved. After the incorporation of RAP, the interface was more complex and there were many micron-scale holes, cracks, and other defects; after high-temperature immersion, the polyurethane binder appeared to show a certain degree of peeling at the holes of the RAP surface. After freeze-thaw, the polyurethane binder on the surface of the mixture produced many cracks. The study of polyurethane cold-recycled mixture is of great significance to realize green construction.

Laboratory Performance Evaluation of Alternative Approaches to Incorporate Recycled Binder Availability into Mixture Design Procedures

There is currently uncertainty in how to properly account for partial recycled binder availability within asphalt mixture design procedures so that content of recycled asphalt materials (RAM) can be maximized while still achieving good performance. This study evaluates and compares two alternative approaches to consider partial availability in mixture design: availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC). The AAMD method revises the calculation of volumetric properties by considering unavailable binder as part of the bulk aggregate volume and uses the RAM gradation to design the aggregate structure. In the COAC method, a mixture is first designed following the conventional Superpave procedures and then a specified increase to the virgin asphalt content is made. Two “control” mixtures containing RAM are evaluated that were originally designed according to the standard Superpave method. Alternative designs were prepared according to the COAC and AAMD methods while maintaining the RAM content in the respective control mixture. Baseline virgin mixtures and one mixture designed following the AAMD method with higher reclaimed asphalt pavement (RAP) content were also prepared. The cracking and rutting performance of the resultant mixtures was evaluated. The results show that the AAMD and COAC approaches lead to an improved cracking performance compared with the control mixtures even for the mixture designed with AAMD at a higher RAP content. However, the mixture designs prepared according to the COAC method presented increased rutting whereas the AAMD mixtures remained at the same level as their respective control mixture.