Reclaimed Asphalt Pavement Content Research Articles

The influence of residual asphalt material in the mechanical behaviour of soil-RAP mixtures for use in paving

ABSTRACT The evaluation of Reclaimed Asphalt Pavement (RAP)’s suitability for pavement layers, optimises resource use, reduces environmental impact, and supports cost-effective practices. In this sense this study aimed to characterise soil-RAP mixtures to ensure they meet the quality standards required for pavement applications. The study examined two types of soil mixtures: one soil-RAP aggregates and the other soil-virgin aggregates (VAM) to understand the impact of residual asphalt binder on aggregate particles. Various mass contents (30%, 50%, 70%, and 90%) were tested alongside conventional soil-gravel mixtures with equivalent proportions and gradation of RAP and VAM. Additionally, the study investigated the effect of adding 2% cement on the performance of both recycled soil-RAP mixtures and conventional soil-gravel mixtures. The analysis includes granulometry, Atterberg Limits, MCT (Miniature, Compacted, Tropical) classification, soil chemical characterisation and microscopic images, compaction in Modified Proctor Energy, CBR, Resilient Modulus tests and stress–strain analysis. The results have revealed that the residual asphalt binder, surrounding RAP aggregates, has reduced the soil mixtures’ strength for different RAP contents. However, the study demonstrated that the addition of cement rendered the soil-RAP mixture feasible, enabling the application of the studied mixtures of RAP to constitute subbase and base layers.

Effect of Chemical Composition on Rheological Properties of Asphalt Binders Modified with Rap Binders and Rejuvenator

Conventional rejuvenating agents such as virgin binders, polymers and so on, poses environmental, technical, and economic challenges. The objective of this study is to investigate the interaction between chemical components and rheological behavior of hot mix asphalt modified with RAP binder and diesel engine waste oil (DEWO) as rejuvenator. 7.2% DEWO was added to the RAP binder to achieve the modified binder (MB), and the effects of the rejuvenator through the MB were evaluated at varying percentages (0 to 100% by weight of the virgin binder) using Dynamic Shear Rheometer (DSR) under short and long-term aging at high and intermediate temperatures, as well as low temperatures using Bending Beam Rheometer (BBR). Saturates, aromatics, resins, and asphaltenes (SARA)-separation, Indirect tensile stiffness modulus test (ITSM), and fatigue life test were also employed to investigate the interaction between chemical components and rheological properties of binder. Results indicated that incorporating 50% modified RAP binder significantly enhanced the performance of the asphalt mixtures, it was also discovered that 100% of RAP content meets standard specifications when modified with oil rejuvenators. This research suggests that large quantities of diesel engine waste oil can be diverted from landfills and employed as useful resource in asphalt production.

Sustainability of Asphalt Mixtures Containing 50% RAP and Recycling Agents

The substitution of virgin asphalt binder with reclaimed asphalt pavement (RAP) has environmental and economic merits, however, cracking susceptibility arises due to the aged asphalt binder within RAP. The objectives of this study are to (1) enhance the cracking resistance of asphalt mixtures containing 50% RAP utilizing recycling agents (RAs) derived from six petroleum-based and bio-based materials, (2) conduct an environmental impact assessment (represented by global warming potential “GWP”) for high-RAP mixtures including RAs, and (3) estimate the cost effectiveness of including high-RAP content in asphalt mixtures. Based on the RAP asphalt binder performance grade (PG), base asphalt binder PG, and RAP content, the RA contents were determined to achieve a target asphalt binder of PG 76-22. A control mixture was benchmarked for comparison, specified for high-traffic volume roads, and contained PG 76-22 polymer-modified asphalt binder. The engineering performance of studied asphalt mixtures was evaluated using the Hamburg wheel-tracking (HWT), semi-circular bend, Illinois flexibility index, Ideal cracking tolerance, and thermal stress-restrained specimen tensile strength tests. It was found that petroleum-derived aromatic oil, soy-based oil, and tall oil fatty acid-based RAs demonstrated a successful restoration of aged RAP asphalt binder without compromising the permanent deformation resistance. The 50% RAP mixtures emitted less GWP by 41% and 42.9% using petroleum- and bio-oil RAs, respectively, and achieved a 31% cost reduction compared to the control mixtures.

Influence of field aging on viscoelastoplastic performance of rubberized asphalt mixtures incorporating reclaimed asphalt pavement in arid urban climate

This study investigates the effects of reclaimed asphalt pavement (RAP) and crumb rubber-modified asphalt (CRMA) on the viscoelastoplastic properties of asphalt mixtures under a range of aging conditions. Six asphalt mixtures, with varying RAP contents (0 %, 30 %, and 50 %) and CRMA modifications, were evaluated through dynamic modulus (|E*|) and flow number (FN) analyses. The specimens were subjected to authentic field-aging conditions for periods of 0, 3, 6, and 9 months. The results reveal that increasing RAP content enhances volumetric properties, Marshall stability, and rutting resistance. CRMA significantly improves fatigue performance and further bolsters rutting resistance, although some detrimental effects are observed at lower temperatures. Aging has a pronounced impact on the mixtures’ performance, particularly on |E*|, Prony series coefficients, viscoelastic strain (εve), and viscoplastic strain (εvp). Newly proposed aging indices, the dynamic modulus aging index (DMAI) and viscoplastic aging index (VPAI), effectively capture the changes in viscoelastoplastic behavior under different aging durations. These findings underscore the potential of RAP and CRMA to enhance pavement durability, prolong service life, and contribute to the development of sustainable and resilient infrastructure. The research offers valuable insights into the performance of asphalt mixtures incorporating RAP and CRMA under real-world conditions.

Effect of Bio-Oils and Wastewater Sludge on the Performance of Binders and Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content.

Waste Cooking Oil (WCO), Soy Oil (SO), and Wastewater Sludge (WWS) have great potential to increase reclaimed asphalt pavement (RAP) content for economic and environmental benefits. This study explored the effects of SO and WCO on rutting, fatigue cracking, and low-temperature cracking performance of binders and Hot Mix Asphalt (HMA) with high RAP content. The potential effect of WWS on the performance and compaction efforts of high RAP content mixes at a 10 °C (50 °F) lower compaction temperature than the control compaction temperature was also investigated. The results indicated that 85% of the RAP binders can be incorporated while maintaining similar performance compared to the control by using 15% SO or 12.5% WCO as a rejuvenator with 2.5% virgin binder. Adding 1% WWS by weight of the total binder improved the binder's rheological properties, the mix's cracking performance, and the mix's density at lower compaction temperatures.

Unveiling the composite rejuvenator efficacy on performance improvement of asphalt binder including high RAP contents

Since the incompatibility between crumb rubber (CR) and reclaimed asphalt binder (RAB) can cause sedimentation and limit its application, this study employed waste cooking oil (WCO) to pre-treat CR particles at different CR/WCO ratios, and assessed its impact on performance of asphalt binders including 30 % and 50 % RABs. Anti-aging and rejuvenation potentials of corresponding composite rejuvenators in binder blends were explored by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) tests, while the performance of corresponding binder blends was evaluated by bending beam rheometer (BBR), linear amplitude sweep (LAS), and multiple stress creep recovery (MSCR) tests. Furthermore, correlation analyses were performed to explore the relationships between the chemical and rheological parameters with a significance level below 0.05. The results confirmed the rejuvenation efficacy of composite rejuvenators in high RAB, and improvement in the critical low temperature of binder blends to a higher performance grade (PG) level compared to the non-treated CR modified binder. In addition, the fatigue cracking resistance was improved at the strain levels higher than 4 % in LAS test. However, the pre-swelled CR fairly compromised the rutting performance of binder blends compared to non-treated CR, its performance was still better than virgin binder. The correlation analysis suggested that it is possible to use chemical parameters as indicators for evaluating certain rheological properties.

High-quality utilization of reclaimed asphalt pavement (RAP) in asphalt mixture with the enhancement of steel slag and epoxy asphalt

Achieving high-quality utilization of reclaimed asphalt pavement (RAP) is challenging due to the subpar technical performance of aggregates and the aging of asphalt within RAP. This study investigates the use of epoxy asphalt (EA) and steel slag to enhance recycled asphalt mixtures (RAM) for superior performance and increased RAP content. The rheological performance of epoxy asphalt (EA) was evaluated using a dynamic shear rheometer (DSR), and its curing process was analyzed. Steel slag-epoxy recycled asphalt mixtures (SRAM) with 40 %, 80 %, and 100 % RAP were prepared, and their road performance was assessed through Marshall, wheel tracking, and semi-circular bending tests. Additionally, the effects of steel slag’s surface morphology and element distribution on moisture and skid resistance were examined. The volatile organic compound (VOC) emission characteristics were also studied. The results show that EA forms a uniformly dispersed structure, providing excellent high-temperature deformation resistance. EA and steel slag significantly enhanced the road performance of SRAM, with SRAM-80 (80 % RAP, 20 % steel slag) achieving a dynamic stability of 15027 times/mm. Steel slag improved SRAM-80’s skid resistance, with a British pendulum number (BPN) of 68 and a texture depth (TD) of 0.5889 mm. Compared to 60/80 asphalt, EA reduced VOC emissions by over 75 %. Incorporating 80 % RAP and 20 % steel slag into RAM effectively utilizes RAP while enhancing performance.

Assessment of aging behaviour of reclaimed asphalt binders: multi-scale mechanical and microstructural characterisation

This study provides a comprehensive multi-scale characterization of the aging resistance of reclaimed asphalt pavement (RAP) binder blends. The analysed samples included different dosages of a RAP binder and a recycling agent (REC). At low strain levels (2.5% and 5%), the use of up to 40% RAP did not adversely affect the Nf value; however, the effect of RAP was clear at 10% strain in the macro scale. At the microscopic scale, the AFM analysis showed that among all samples, the 100% RAP binder was affected the least by laboratory aging. However, the aging susceptibility increased as the RAP content increased from 0 to 40%. A plausible explanation is that the effects of laboratory aging (temperature and/or pressure) became more concentrated on the base binder when its quantity decreased in the blends. The use of REC reduced the stiffness of the unaged blends, but its effect diminished upon further aging of the blends.

A Critical Overview of Using Reclaimed Asphalt Pavement (RAP) in Road Pavement Construction

In view of the climate crisis, green technologies should be used to ensure sustainable structures in the construction industry. Road construction could also contribute to the creation of a circular economy, as it is partly responsible for several current environmental phenomena, such as greenhouse gas (GHG) emissions and depletion of natural aggregates and landfills. The use of Reclaimed Asphalt Pavement (RAP) is considered one of these recycling solutions, as it can be reused in road construction projects. Implementing it in practice is already a topic that should be included in the technical guidelines for road construction and maintenance. Therefore, this study is a critical overview of the worldwide experiences with the installation of RAP in road pavements published by different road authorities worldwide, aiming to prove the inconsistency in using these materials in pavement courses. The results of this review are analyzed to identify possible knowledge gaps regarding RAP content. It was shown that the use of RAP is different on all five continents. The main findings were that the RAP content in asphalt layers is still at a low level of about 30% and that the use of RAP materials in unbound layers in road pavement construction is not yet fully accepted. It is expected that the results of this study will help to improve further research on the performance of RAP and motivate more countries to develop appropriate guidelines for the use of RAP materials in road pavement construction.

Aggregate uniformity of recycled asphalt mixtures with RAP from refined decomposition process: Comparison with routine crushing method

In consideration of skyrocketing price in pavement materials and ever-increasing attention to environment preservation, the utilization of reclaimed asphalt pavement (RAP) into asphalt mixtures has gained more and more favor. However, the uniformity of virgin and RAP aggregate in recycled asphalt mixtures (RAM) has not yet been studied due to the difficulty in informational extraction of multi-structures. To address this, white dolomite was used as virgin aggregate to be distinguished from RAP aggregate based on their color difference. The shear gyratory compactor specimens of RAM were prepared and saw-cut, and then meso-structures including virgin aggregate, RAP aggregate and asphalt mortar were extracted using digital image processing (DIP) technology. The DIP processes mainly involved retention of blue channel for image graying, newly proposed double-threshold OTSU method for image segmentation and image morphology processing. The aggregate uniformity index (AUI) was proposed based on the coefficient of variation of aggregate area ratio. The influences of RAP that were pre-processed by refined decomposition (RD) and routine crushing (RC) and its content on the aggregate uniformity were evaluated. The results demonstrate the efficacy of the improved DIP approach, as evidenced by the maximum mean absolute error between laboratory-measured and image-estimated gradation that is lower than 7.8 %. The addition of RAP into asphalt mixtures is adverse to the aggregate uniformity. The higher the RAP content, the inferior the aggregate uniformity of RAM, which attributes to the agglomeration of RAP materials. RAP agglomeration leads to the heterogeneity of RAP aggregate and thus dominates the heterogeneity of the whole aggregate. Therefore, the aggregate uniformity of RAM produced by RD-RAP is superior to that produced by RC-RAP. The superior degree is 9 %.

Laboratory evaluation of synergistic blending with SBS-modified bitumen and rejuvenator to enhance the performance of recycled bitumen with a high content of RAP materials

Reclaimed asphalt pavement (RAP) stands as a pivotal construction material widely used in asphalt pavement rehabilitation. The prevailing focus and trajectory revolve around increasing the proportion and utility of RAP materials. However, the potential for temperature and fatigue cracking increases with the dosage of RAP materials. In this study, SBS modified bitumen (SBSMB) and four rejuvenators were combined synergistically with aged asphalt to enhance the performances of the recycled bitumen with high RAP content and consequently augment the value of the RAP material, all while ensuring compatibility between the SBSMB and aged base bitumen. Initially, the base bitumen was aged using a pressure aging vessel (PAV) test. Subsequently, a selection of virgin bitumen (VB), SBSMB, and four rejuvenators were utilized to revitalize the aged bitumen. A comprehensive battery of tests, encompassing conventional tests, temperature sweep, frequency sweep, multiple stress creep recovery (MSCR), bending beam rheometer (BBR), and linear amplitude sweep (LAS), were carried out to characterize the rheological properties. Finally, Fourier transform infrared spectroscopy (FTIR) was employed, along with the determination of polystyrene index (IPS) and polybutadiene index (IPB), to evaluate the compatibility between SBSMB and aged base bitumen. The results underscore that the incorporation of SBSMB and rejuvenator comprehensively enhances high-temperature performance and fatigue cracking resistance while effectively reinstating low-temperature cracking resistance. Furthermore, the values of IPS, IPB, and IPS/IPB exhibit an increase with the addition of a rejuvenator, indicating its potential to improve the compatibility between SBSMB and aged base bitumen. Thus, this research proposes a more cost-effective and environmentally sustainable approach to bolstering conventional asphalt pavement performance and grade.

Visco-plastic deformation characteristics of accelerated-aging asphalt mixture containing reclaimed asphalt pavement regenerated with crumb rubber based on Hamburg Wheel-Track test

The regeneration of the reclaimed asphalt pavement (RAP) with incorporation of crumb rubber was a cleaner alternative for reducing the fossil and ore resources consumption. For the desert area like Egypt, the rut of reclaimed pavement was principal contradiction during a long service. This work mainly characterized the visco-plastic deformation of accelerated-aging rubberized reclaimed asphalt mixture based on Hamburg Wheel-Track test. Four mixtures were designed by two contents of RAP (15% and 30%), two contents of crumb rubber (5% and 15%), and two asphalts (pen-#70 and pen-#90). Specifically, this work focused on the determination of accelerated aging effect, and analysis of rutting deformation fitting including overall deformation and visco-plastic deformation. Then, effect of accelerated aging time and material compositions on visco-plastic deformation was analyzed. In addition, the correlation analysis among indicators evaluating rutting deformation of mixture was conducted, and the correlation analysis between rutting deformation of mixture and average recovery rate at 3.2 kPa of extracted bitumen was completed. The results demonstrated that the accelerated aging equivalent factor of sunlight was approximately 6, meaning that one day of accelerated aging was equivalent to six days of natural aging in Cairo. With the accelerated aging time increased, resistance to rutting deformation of rubberized reclaimed asphalt mixture was promoted with the incorporation of RAP, crumb rubber and soft matrix binder. Meanwhile, dynamic stability, derived from fitting curve of visco-plastic deformation, was positively correlated with accelerated aging time, and it could accurately evaluate visco-plastic deformation characteristics of reclaimed mixture. Finally, visco-plastic deformation characteristics of reclaimed mixture was closely related to the permanent deformation resistance of binder at high temperature.

Performance of asphalt mixtures containing high reclaimed asphalt pavement and waste steel rolling oil

Reducing costs, dealing with environmental problems, and preserving more natural resources are among the main incentives for reusing asphalt instead of road reconstruction. However, asphalt reuse involves the addition of some modifiers to the asphalt mixture. In this respect, rejuvenators investigated in the previous studies did not perform properly against all failures. Besides, they had problems such as lacking access to the required amount for road construction and high production costs. Regarding the high-temperature resistance and antioxidant properties of the waste steel rolling oil (WSRO), for the first time, the effect of using this lubricant was investigated on the recovery of bitumen aging and the performance of asphalt mixture containing high amounts of reclaimed asphalt pavement (RAP). To this end, the conventional (penetration and softening point) tests and rotational viscosity test were conducted to determine the optimal amount of rejuvenator. In addition, FTIR and FESEM tests were carried out for chemical and morphological investigation. SCB and dynamic creep tests were performed on a balanced mix design to examine the performance against cracking and rutting. Moisture sensitivity was also investigated by performing an indirect tensile test. The results show that a uniform texture was created in the aged bitumen modified with WSRO, and there was a decrease in functional groups that represent the occurrence of aging. Therefore, WSRO can restore aging and improve rutting and cracking performance. Resistance to moisture sensitivity also improved. Overall, the results show a performance improvement in the mixture containing high RAP content mixed with WSRO as a waste rejuvenator. However, more studies encompassing rheological, economic and environmental aspects, are needed to conclude about the practical use of this material.

Enhancing self-healing of asphalt mixtures containing recycled concrete aggregates and reclaimed asphalt pavement using induction heating

Given the growing demand for sustainable road construction materials, this research aims to evaluate the synergistic effects of incorporating recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) in asphalt mixtures. Induction heating was also utilized to enhance the self-healing ability of asphalt mixtures, with the intention of prolonging their lifespan and mitigating environmental impacts. This research assessed the pavement performance of recycled asphalt mixtures (RAM) with different RCA and RAP dosages. The induction heating performance, cooling performance, and effective heating depth of RAM were tested. Lastly, the cumulative healing efficiency of the RAM was evaluated under multiple "fracture-healing" conditions. Findings indicated that the inclusion of RCA and RAP negatively influenced the water stability, high-temperature deformation resistance, and crack resistance at low temperatures of the RAM. However, when the RCA content was 20 % and the RAP content did not exceed 20 %, the road performance of the RAM met the requirements. The contents of the RCA and RAP had no discernible effect on the RAM's induction heating capability. Moreover, when the RCA content was 20 % and the RAP content did not exceed 10 %, the effective heating depth of the RAM could reach 50 mm. Using fracture energy recovery rate as the healing index, after three cycles of "fracture-healing", the RAM with 20 % RCA achieved the highest cumulative healing efficiency of 291 %. The cumulative healing efficiency of recycled asphalt mixtures with 20 % RCA and 10 % RAP was close to that of normal asphalt mixtures. This research contributes to reducing the consumption of non-renewable resources, minimizing environmental impact, and maintaining or even improving the performance of asphalt pavements by optimizing the use of RCA and RAP.

Optimising waste cooking oil as rejuvenator for recycled mixtures: a laboratory-based approach

Global waste accumulation necessitates sustainable pavement solutions. This study focuses on sustainable pavements by adopting the waste-to-wealth approach using waste cooking oil (WCO) as rejuvenator to incorporate higher reclaimed asphalt pavement (RAP). A novel approach optimises WCO for recycled mixtures with different field RAP contents. The optimum WCO was assessed for mixtures with laboratory-aged RAP, considering binder performance, properties of laboratory-aged RAP binder, and moisture susceptibility. Optimum dosages were then determined for the mixtures with field RAP without compromising moisture susceptibility. These dosages depend on the percentage and viscosity of the extracted binder of field RAP. Results indicated that the recycled mixture with field RAP and corresponding optimum WCO assessed from the proposed method exhibited satisfactory moisture susceptibility unlike the recycled mixtures without WCO. Also, the method suggested a way to estimate the total optimum binder content, if higher RAP is being used considering the inactive binder of RAP.

The Effect of Refined Separation on the Properties of Reclaimed Asphalt Pavement Materials

Refined separation not only controls the variability of reclaimed asphalt pavement (RAP), but also improves the mixing ratio of RAP and the quality of recycled asphalt mixtures. This study examines RAP treated with various refined separation frequency parameters, analyzes the variation rules and the variability of RAP aggregate gradation, asphalt content, asphalt properties, and aggregate properties, and calculates the maximum mixing percentage of coarse RAP material by using the gradation variability control method and the asphalt content variability control method. The results show that the variability of gradation and asphalt content of coarsely separated RAP is considerable, and a refined separation process significantly reduces the variability of gradation and asphalt content of RAP; the agglomeration of RAP decreases with an increase in the refined separation frequency; and the RAP agglomeration of three kinds of RAPs (E1, E2, and E3) under a refined separation frequency of 55 Hz reduces by 6.40%, 4.30%, and 4.30%, respectively, as compared with that of coarsely separated RAPs. The asphalt content of the refined separation RAP gradually decreases with an increase in frequency, and the asphalt content of E1 and E2 (55 Hz) was only 0.95% and 1.10%, respectively. The maximum percentage of RAP in recycled asphalt mixtures was calculated using the gradation variability control method and the asphalt content variability control method, respectively. The maximum proportions of RAP were 45% and 33% for A1 (0 Hz), respectively, and the maximum proportions of RAP for E1 (55 Hz) were all 100%. The results of the two methods show that the process of refined separation can increase the maximum proportion of blended RAP materials. They also demonstrate that the refined separation process can increase the maximum blending ratio of coarse RAP materials, thereby improving the quality of the RAP, increasing the proportion of RAP blending, and ensuring the quality of the recycled asphalt mixture. In conclusion, the refined separation process holds promise for maximizing the potential value of RAP and optimizing its recycling, environmental, and economic benefits.

Development and evaluation of fiber-enhanced RAP interlayer for HMA overlay treatment

To scientifically and efficiently utilize reclaimed asphalt pavement (RAP) generated during asphalt pavement maintenance, and to promote resource recycling and sustainable development, this paper developed and evaluated the Fiber-enhanced RAP interlayer for HMA overlay and preservation treatments. In this paper, RAP interlayer was designed based on the Response Surface Methodology (RSM) and the pull-out strength and the shear strength of were tested. Through double-objective optimization and analysis, the recommended proportions were determined as 2.22 kg/m2 of rubber asphalt, 10.57 kg/m2 of aggregate, and 30% RAP content. Subsequently, the effects of different basalt fiber contents on the pull-out strength, shear strength, flexural strength, fatigue life, and permeability coefficient of asphalt mixture with interlayer containing RAP were investigated. The results indicated a significant improvement in these properties with an 80 g/m2 basalt fiber content. The performance of asphalt mixture with Fiber-enhanced RAP interlayer was obviously superior to the asphalt mixture with interlayer without fiber and RAP. According to the test results of Digital Image Correlation (DIC), it was found that basalt fibers effectively reduce stress concentration, delaying the initiation and propagation of cracks.

Experimental and predictive study of self-compacting concrete containing reclaimed asphalt pavement

This work focuses on the reuse of reclaimed asphalt pavement (RAP) in the production of self-compacting concrete (SCC) for usage in the construction of rigid pavements. The article first describes an experimental study where five SCC mixtures incorporating 0%, 20%, 40%, 60% and 100% volumetric substitutions of natural aggregates by RAP were formulated. Several characterisation tests in the fresh and hardened states were then performed. The results of all performed tests showed that RAP has a slight negative effect on SCC performance in the fresh state. The most significant reduction observed does not exceed 18% for slump-flow and 10% for L-shaped box values when total substitution is applied. Furthermore, the mechanical properties noticeably decrease with an increase in RAP content, with reductions of up to 37% in 28-d compressive strength and 23% in 28-d indirect tensile (IDT) strength observed in the case of full replacement. However, it is possible to formulate SCC mixtures even with 100% RAP substitutions and meet specifications for rigid pavement construction. In addition, modelling of the various mechanical characteristics made it possible to find out the reason behind the reduction in these properties with RAP content. In fact, the thin bitumen film around RAP particles weakens their surface adhesion with the hydrated cement paste. With the intrinsic RAP properties found, the hardened-state characteristics of any other SCC mixture incorporating RAP could be predicted.

Assessment of the effectiveness of binder fatigue, rheology and chemistry parameters in evaluating cracking resistance in high RAP mixtures modified with recycling agents

The utilization of Reclaimed Asphalt Pavement (RAP) in pavement construction has gained prominence as a sustainable approach to reduce material costs and environmental effect. However, a significant challenge associated with increased RAP incorporation lies in the potential fracture distress caused by the aged binder. The purpose of this study is to assess the cracking performance of asphalt mixtures incorporating three levels of recycled materials (30% RAP, 50% RAP, and 30% RAP along with 5% Reclaimed Asphalt Shingles (RAS)). Three softening oils were employed to improve the cracking performances at two aging levels. Performance evaluations, including cracking performance assessments at intermediate and low temperatures, were carried out and compared with control mixtures. The findings of this study reveal that the incorporation of softening oils, as investigated herein, offers a viable means of producing asphalt mixtures featuring high RAP content while preserving performance comparable to that of a virgin mix. From a binder perspective, the Glover–Rowe (G–R) parameter and fatigue life at 10% strain level emerge as robust indicators for evaluating cracking resistance under conditions pertaining to intermediate and low temperatures.

Analysis of the Degree of Blending (DoB) of recycled asphalt mixtures with variation in mixing temperature, type, and RAP content

Presently, there is a significant increase in studies dedicated to the reuse of Reclaimed Asphalt Pavement (RAP) material obtained from the recycling of asphalt coatings. This procedure aims to reduce production costs and minimize environmental impacts. To carry out the reuse of this material, it is crucial to understand the interaction mechanisms between the aged binder of the RAP and the new binder. These mechanisms can be assessed through the Degree of Binder Activity (DoA) and the Degree of Blending (DoB). DoA represents the quantity of aged binder available for the new mixture, being an intrinsic property of each RAP. On the other hand, DoB indicates the degree of blending between the aged and new binders, being influenced by external factors such as mixing parameters, thus presenting a challenge in quantification. This study sought to establish a predictive model to quantify DoB based on Dynamic Modulus and Fourier-Transform Infrared Spectroscopy (FTIR) tests. These tests were conducted on mixtures containing four different RAPs, varying in different content levels and mixing temperatures. In each RAP, DoA was quantified, and a statistical analysis was performed to verify the significance of independent variables in dynamic modulus results. After this step, four modeling attempts were made, choosing the one that not only presented significant independent variables but also obtained the highest predicted R² value. The chosen model was validated and demonstrated small variations compared to DoB obtained by the generated equation. Thus, it is concluded that the DoB modeling conducted in this study highlights that mixing temperatures and RAP content influence factors such as DoA, dynamic modulus, FTIR, and consequently, DoB. Additionally, the practicality of the model was emphasized, as it successfully predicted DoB using a single mechanical and chemical test.