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The goal of the research presented in this report is to study how the mechanical properties of hot mix asphalt change upon the addition of high contents of reclaimed asphalt pavement (RAP) and the inclusion of any amount of recycled asphalt shingles (RAS), with between 25% and 50% binder replacement and to consider the addition of recycling agents to reduce the increase in stiffness and corresponding decrease in fatigue resistance. To achieve this goal, 16 mixes and the corresponding binders were fabricated and tested in the laboratory. The mix factorial includes a control gradation, two virgin binders (PG 64-16 and PG 58-28, from different sources), two RAPs with different levels of aging (PG high temperatures of 102°C and 109°C), one RAS, and two recycling agents (a petroleum-derived aromatic and a tall oil). The testing of the binders included performance grade (PG), shear stiffness, and Fourier transform infrared spectroscopy. The testing of the mixes included stiffness, four-point flexural fatigue resistance, rutting resistance, and the IDEAL cracking tolerance (IDEAL-CT) test. The main conclusion from this study is that most of the increased stiffness effects of high RAP and/or RAS addition can be offset by using recycling agents and/or reducing the stiffness of the virgin binder by reducing the PG binder grade. Two approaches are proposed to determine an appropriate dosage of recycling agent. The first focuses on restoring the mechanical properties of the mix with high RAP/RAS content back to the properties of a control mix with either no RAP/RAS or a low RAP/RAS content. The second approach focuses on meeting the required performance-related specifications within the balanced mix design framework by using the minimum amount of recycling agent. It was found that restoring the PG high temperature of the binder blend, a commonly followed approach, may result in unnecessarily high recycling agent doses with a consequent increase in cost and greenhouse gas emissions and the over-softening of the mix at intermediate and low temperatures.

Current Caltrans Standard Specifications for rubberized hot mix asphalt–gap-graded (RHMA-G) do not allow the inclusion of reclaimed asphalt pavement (RAP). This report summarizes the research conducted by the UCPRC in support of the Caltrans-industry initiative “10% RAP in RHMA-G,” whose goal is to evaluate the use of up to 10% RAP (by aggregate replacement) in RHMA-G mixes, provided that the research does not identify significant potential problems for durability. Five pilot projects were built by Caltrans as part the initiative. In each of the pilots, a control RHMA-G (without RAP) and an RHMA-G with 10% RAP were placed. The mixes were sampled during production and tested using performance-related tests at the UCPRC laboratory. The results of the testing of the mixes—including stiffness, four-point bending fatigue resistance, and rutting resistance—indicate that the addition of 10% RAP had minor effects on the mechanical properties of the RHMA-G. With just a few exceptions related to changes in the total binder content of the mix, the effect of the RAP addition was negligible compared with project-to-project differences. Modeling with CalME software based on four-point bending testing results indicated that the impact of the RAP addition on the cracking performance of the pavement was either negligible or comparable to project-to-project differences. From the constructability point of view, the addition of the RAP did not create any problems. The life cycle assessment presented in this report indicates that the addition of 10% RAP to the RHMA-G can reduce the greenhouse gasses emissions associated with the RHMA-G production (cradle-to-gate) by up to 5%.

The goal of the research presented in this report is to study how the mechanical properties of hot mix asphalt change upon the addition of high contents of reclaimed asphalt pavement (RAP) and the inclusion of any amount of recycled asphalt shingles (RAS), with between 25% and 50% binder replacement and to consider the addition of recycling agents to reduce the increase in stiffness and corresponding decrease in fatigue resistance. To achieve this goal, 16 mixes and the corresponding binders were fabricated and tested in the laboratory. The mix factorial includes a control gradation, two virgin binders (PG 64-16 and PG 58-28, from different sources), two RAPs with different levels of aging (PG high temperatures of 102°C and 109°C), one RAS, and two recycling agents (a petroleum-derived aromatic and a tall oil). The testing of the binders included performance grade (PG), shear stiffness, and Fourier transform infrared spectroscopy. The testing of the mixes included stiffness, four-point flexural fatigue resistance, rutting resistance, and the IDEAL cracking tolerance (IDEAL-CT) test. The main conclusion from this study is that most of the increased stiffness effects of high RAP and/or RAS addition can be offset by using recycling agents and/or reducing the stiffness of the virgin binder by reducing the PG binder grade. Two approaches are proposed to determine an appropriate dosage of recycling agent. The first focuses on restoring the mechanical properties of the mix with high RAP/RAS content back to the properties of a control mix with either no RAP/RAS or a low RAP/RAS content. The second approach focuses on meeting the required performance-related specifications within the balanced mix design framework by using the minimum amount of recycling agent. It was found that restoring the PG high temperature of the binder blend, a commonly followed approach, may result in unnecessarily high recycling agent doses with a consequent increase in cost and greenhouse gas emissions and the over-softening of the mix at intermediate and low temperatures.

The thermal equilibrium of asphalt mixtures, when combined with reclaimed asphalt pavement (RAP), forms the foundation for high-quality hot pavement recycling. This study focuses on quantifying the thermal equilibrium process of recycled asphalt during mixing. To achieve this objective, a typical RAP content of 20% was utilized in preparing the recycled asphalt. In the experiments, three preheated RAP temperatures were considered to reflect different practical scenarios. Thermal images of recycled asphalt were captured throughout the entire mixing process from 10 s to 90 s in order to characterize the temperature evolution pattern of recycled asphalt mixtures. In addition to experiments, discrete element simulation was conducted to elucidate additional details regarding temperature exchange. The results indicated that the initial thermal equilibrium during mixing may have a significant impact on RAP dispersion and temperature variation, while the subsequent mixing period has limited influence on the final thermal state. Furthermore, it is observed that complete thermal equilibrium cannot be achieved due to the nonuniform distribution of RAP at the end of mixing. In addition, a model describing the temperature evolution of RAP is proposed in this study, which demonstrates a good fit with the data. [ABSTRACT FROM AUTHOR]

The granular bases commonly used in the construction of road infrastructure projects often require a high consumption of raw materials. The potential utilization of recycled materials, specifically Reclaimed Asphalt Pavement (RAP) derived from road asphalt pavement demolition, emerges as a promising sustainable advantage for infrastructure projects, considering its potential environmental and cost benefits in other layers of the structure. In this context, this research proposes a feasibility study on the use of RAP as a granular base layer, supported by an advanced laboratory analysis that includes a range of tests simulating the in-service conditions as well as a full-scale demonstration of the material behavior under static and dynamic loads. Various design variables, such as different gradations and binder content, are considered. The results demonstrate that, despite having discontinuous gradation and smaller aggregate sizes than those commonly applied in natural base layers, the evaluated recycled materials exhibit a higher load-bearing capacity and resistance to permanent deformation than the reference materials commonly used as granular bases. Notable enhancements of up to 30% in elastic modulus, coupled with reductions of around 20% in permanent deformations, have been documented using the asphalt cement potential in the old pavement. [ABSTRACT FROM AUTHOR]

The use of reclaimed asphalt pavement (RAP) has brought enormous potential economic and environmental benefits to society. However, the cluster phenomenon of RAP particles in recycled hot-mix asphalt (HMA) has limited the extensive usage of RAP to a certain extent. Therefore, this research evaluated the effect of the original clustering degree of RAP and design parameters on the properties of recycled HMAs and the qualitative status of RAP cluster in recycled mixes. Six groups of mixes were designed, including one control group in which the RAP particles were designed as completely no cluster status, three experimental groups in which the RAP particles were designed at different original clustering degrees, and another two groups designed under different preheating temperatures and blending time. Then, the volumetric indicators, water stability, rutting, thermal cracking, and abrasion performance of each group were evaluated. It can be found that the RAP cluster was partially dispersed during the mixing and varied with different design parameters. The incomplete dispersion of fine RAP cluster acted as a "fake coarse aggregate" and affected the volumetric results and performance of final mixtures. Therefore, it may be inaccurate to design the aggregate gradation of recycled HMAs solely based on the extracted curve or the black curve of original RAP particles. The dispersion process of the RAP cluster during the mixing should not be ignored. In addition, the results also indicated that the original clustering degree of RAP particles may need to be carefully controlled during the construction. [ABSTRACT FROM AUTHOR]

The migration of reclaimed asphalt pavement (RAP) mastic into the recycled hot-mix asphalt (RHMA) mixture system during the hot-mix process results in varying dispersion degrees of RAP aggregates within RHMA, impacting its durability. This study aimed to investigate the impact of hot mix parameters on RAP dispersion and RHMA performance. The dispersion degree of RAP aggregates in RHMA was determined through slicing and digital image processing. The influence of hot mix parameters on RHMA performance was assessed through rotary compaction, Marshall, moisture-induced sensitivity, and low-temperature bending beam tests. The correlation between the RHMA performance and RAP dispersion degree was analyzed by employing the Pearson correlation coefficient. The findings show that higher RAP content reduces the RAP dispersion degree, whereas the opposite trend was observed for the RAP preheating temperature, RHMA mixing temperature, and RHMA mixing duration. Improving the RAP dispersion degree in RHMA decreased the compacted energy index and air voids in RHMA, thereby enhancing the Marshall stability, moisture stability, and low-temperature crack resistance of RHMA. [ABSTRACT FROM AUTHOR]

In view of promoting the recycling of construction and demolition waste, the re-utilization of Recycled Asphalt Pavement (RAP) as aggregate in structural concrete has been recently proposed and investigated. Although many studies are available on the physical and mechanical characterisation of concrete containing RAP, little is still known about how medium- to long-term durability performances are affected by the partial or total replacement of natural aggregates with RAP aggregate. In this experimental study, several durability-related properties were assessed, with the aim of investigating the possible use of RAP as partial or total replacement of natural aggregates for reinforced concrete applications. In particular, concretes were obtained with increasing RAP contents (from reference mixtures with natural aggregate only, to complete substitution with RAP aggregate), two different cement types (Portland-limestone and pozzolanic), and two water/cement ratios (0.45 and 0.65), representative of two exposure classes for chloride and carbonation induced corrosion. Water sorptivity through capillary suction and water absorption were investigated, together with the resistance to the penetration of carbonation, both under accelerated and natural exposure, and the resistance to the penetration of chlorides, under natural diffusion. Relationships between physical and mechanical properties, such as total open porosity and compressive strength, and durability-related properties were also investigated. Results showed that sorptivity experienced a neat decrease for increasing RAP contents, due to the hydrophobic nature of RAP aggregate, while water absorption was less affected. Resistance to the penetration of carbonation and chlorides were both more clearly affected by other mix design variables, such as w/c ratio and cement type, rather than RAP content. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of different design parameters on the low-temperature crack resistance of recycled asphalt mixtures and to provide design guidance for recycled asphalt mixtures. Three material composition factors (reclaimed asphalt pavement (RAP) content, gradation type, and asphalt content) and four mixing process factors (RAP preheating temperature, mixing duration, mixing temperature, and mixing sequence) were considered. Using a single-factor controlled variable method, AC-20 recycled asphalt mixture was designed to study low-temperature crack resistance through a semi-circular bending (SCB) test, the significance of the effects of different factors was analyzed using the orthogonal test, and the fracture surface morphology was observed. Results show that both material composition and mixing processes impact the low-temperature crack resistance of recycled asphalt mixtures. Specifically, lower RAP content, higher asphalt content, higher mixing temperature, longer mixing duration, and mixing sequence I favor improved low-temperature crack resistance. Gradation type and RAP preheating temperature showed non-linear effects, peaking before declining. Material composition, especially asphalt content, has a more significant effect on the low-temperature crack resistance than mixing process factors. To achieve optimal low-temperature crack resistance, it is recommended to optimize the material composition of recycled asphalt mixture and control the RAP preheating temperature to 110 °C, maintain laboratory mixing duration of at least 150s, set the mixing temperature to at least 160 °C, and follow mixing sequence I. [ABSTRACT FROM AUTHOR]

India's expanding road network is vital for its development, but conventional construction methods using natural aggregates raise environmental concerns due to high energy consumption and CO2 emissions. This study explores the potential of geopolymer stabilised material, a sustainable alternative that utilizes fly ash (FA) and reclaimed asphalt pavement (RAP) to mitigate these issues. FA-based geopolymers harness the pozzolanic activity of fly ash to achieve comparable or improved mechanical and morphological properties compared to traditional concrete. By analysing existing literature, this review examines the impact of FA-based geopolymer stabilized with RAP on various performance aspects such as morphological characteristics, compressive strength, resilient modulus, and durability. This approach promotes a circular economy by utilizing waste materials (RAP) and reduces reliance on virgin resources. The findings highlight the potential for cost-effective and environmentally friendly construction solutions using readily available materials. [ABSTRACT FROM AUTHOR]

In order to study the effect of the crushing process on the fine separation of reclaimed asphalt pavement (RAP) and the mechanical properties of cement-stabilised aggregate mixed with RAP, four crushing processes, namely small mesh hammer crushing, hammer crushing, jaw crushing, and double roller crushing, were used to separate the aggregate from asphalt in RAP materials. The effect of crushing on the grading characteristics and agglomeration condition of RAP material was investigated. RAP cement-stabilised aggregates were prepared and analysed for their mechanical properties and micro-morphology using RAP materials obtained from fine separation. The relationship between the RAP material properties and the mechanical properties of the RAP-added cement-stabilised aggregate was analysed on the basis of the tests. The results showed that crushing breaks down large-size RAP materials, leading to grade refinement, and that hammer crushing was the most effective in reducing the grade variability. The highest agglomerate dissociation rate of RAP material above 4.75 mm after small mesh hammer crushing treatment was 96.9%, and the residual mass ratios of RAP material in two grades of 0~3 mm and 3~5 mm after hammer crushing were lower than 90%. The unconfined compressive strength, splitting strength, and compressive resilience modulus of RAP cement-stabilised aggregate after crushing were greater than those of the uncrushed RAP cement-stabilised aggregate, and the crushing increased the amount of RAP in the mix to 60%. Compared with the unadulterated RAP cement-stabilised aggregate, the hydration products of the RAP cement-stabilised aggregate were reduced after crushing, and there were obvious gaps and discontinuities between the RAP material and the cement paste. The RAP gradation and agglomeration condition correlated strongly with the mechanical properties of the mixes, with RAP coarse aggregate agglomerates being the main cause of gradation variability. This paper provides theoretical support for the proposal of a pretreatment process to reduce the variability of RAP-doped cement-stabilised aggregate and improve the mechanical properties, and the research results are conducive to the recycling of high-volume RAP materials in the base. [ABSTRACT FROM AUTHOR]

This study was set out to conduct a life cycle assessment (LCA) to explore the environmental and economic impacts of pavement design alternatives using reclaimed asphalt pavement (RAP) and recycled plastic. 25 design alternative pavement designs were considered for a four-lane 8 km-long highway section. Design mix percentages varied between 0 and 40% of RAP with 10% increments and 0–20% of recycled plastic with 5% increments. The impact was assessed based on estimating utilized energy and water resources, climate change impact in terms of CO2 equivalent, and air pollution in terms of air acidification, human health particulate (HHP), and photochemical smog. Results show that recycled plastic is superior to RAP in reducing energy consumption and GHG emissions. Both RAP and recycled plastic reduced water consumption. Recycled plastic reduced air acidification, HHP, and smog. RAP also increased HHP substantially, mainly during materials production. It was found that the RAP replacement ratio of 10% yielded the highest value of energy consumption, harmful gases emissions, air acidification, HHP, and Smog. RAP and plastic both reduced costs substantially as recycled material reduced the use of virgin materials and bitumen. In addition, using RAP eliminates the cost of moving RAP to landfills.

Abstract The replacement of natural aggregate in concrete with artificial and/or recycled one has recently gained attention as meaningful strategy to reduce the environmental impact of structural concrete and promote circular economy principles. This study investigated the possibility to use Reclaimed Asphalt Pavement (RAP), in the “as received conditions”, as a partial or complete substitution of natural aggregate for structural concrete. RAP aggregate was firstly characterized in terms of grain size distribution, density, assessment of fines, chloride content, moisture content and water absorption. Subsequently, a total of twenty-four concrete mixes were designed, considering two cement types, two w/c ratios and several aggregate substitution percentages. For each mix, properties at the fresh and hardened state were investigated, such as workability, density and total open porosity, compressive strength, dynamic modulus of elasticity, and electrical resistivity. Results showed that RAP has a good potential to be used in reinforced concrete, provided that different water absorption and moisture content are considered in the mix design. RAP concrete was characterized by a lower density and increased total open porosity; however, an accurate tailoring of the concrete recipe could compensate the strength loss for several applications. Other properties, such as electrical resistivity and the relationship between dynamic modulus of elasticity and compressive strength did not result significantly altered by the presence of RAP.

The utilization of reclaimed asphalt pavement (RAP) in asphalt mixtures not only reduces production costs and resource consumption but also provides significant environmental benefits. Consequently, technology and methodologies used for asphalt pavement recycling, aimed at enhancing the utilization rate of RAPs, have emerged as prominent topics in both academic research and engineering practice. Given the complex thermal history and poor low-temperature performance (LTP) of RAP, investigating the effects of varying thermal histories of RAPs on the LTP of a mixture holds substantial practical significance for increasing the utilization rate of RAP in seasonally frozen regions. In this study, scanning electron microscopy (SEM), the thermal stress restrained specimen test (TSRST), the trabecular bending test, and the bending beam creep test (BBCT) are utilized to examine the effects of the indoor simulation methods that produce RAPs with varying thermal histories and contents on a recycled asphalt mixture (RAM) from both microscopic and phenomenological perspectives. Additionally, this research investigates the accuracy of predicting the LTP of RAMs using the Burgers model. The test results indicate that the LTP of an RAM is influenced not only by the RAP content and its thermal history but also by the ambient temperature. Regardless of the thermal history of the RAP, the LTP of an RAM tends to decrease as the RAP content increases. Different thermal histories of RAPs exert varying effects on the low-temperature viscoelastic behavior of an RAM. The UVRAP reduces the viscoelastic temperature range of an RAM by an average of 10.79%, whereas the THRAP increases it by an average of 2.16%. These effects can be attributed to the distinct micromorphology of the asphalt on the surfaces of RAPs with a varying thermal history. Specifically, a greater number of micropores and microcracks on the asphalt surface leads to a poorer LTP of RAMs. Additionally, the residuals of the Burgers model for predicting the LTP of an RAM with THRAP exceeded −2. However, the Burgers model demonstrates predictive capabilities for evaluating the LTP of an RAM filled with RAP from the same source or with a similar thermal history. [ABSTRACT FROM AUTHOR]

The use of warm mix asphalt (WMA) and reclaimed asphalt pavement (RAP) technologies presents challenges in optimizing binder activation and mechanical performance in asphalt mixtures. This study aimed to evaluate the effects of three WMA additives (sunflower oil, WarmGrip®, and natural zeolite) and different RAP contents (30% and 70%) on the rheological and mechanical properties of recycled asphalt mixtures. The research focused on assessing the degree of RAP binder activation, determining the extent of partial activation, and analyzing the impact on tensile strength, moisture resistance, modulus, fatigue life, and deformation resistance. The methodology included chemical and rheological analysis of RAP and modified binders, as well as mechanical testing of recycled mixtures. Results indicated partial RAP binder activation, with 96.16% activation in mixtures containing 30% RAP and 80.77% in those with 70% RAP. Sunflower oil acted as a rejuvenator, reducing binder stiffness and decreasing the maximum PG temperature by 6 °C. The use of natural zeolite improved moisture resistance, resulting in TSR values 20% higher than those of conventional hot mixtures with the same RAP content (70%). Warm recycled mixtures demonstrated enhanced fatigue life and moisture resistance, particularly with WarmGrip®. Overall, the incorporation of WMA additives allowed for enhanced fatigue life and deformation resistance in recycled mixtures, enabling the use of up to 70% RAP without compromising mechanical performance. The findings support the potential of WMA and RAP additives to improve sustainability, cost-effectiveness, and durability in asphalt pavement construction. [ABSTRACT FROM AUTHOR]

The frictional properties of aggregates play a significant role in determining pavement skid resistance. To preserve natural aggregates, reclaimed asphalt pavement (RAP) has been widely used for decades. However, its use in pavement surface courses is often limited due to its unknown frictional properties. Therefore, this research aimed to quantitatively investigate both aggregates and RAP to develop a quick evaluation method for frictional properties. Nine types of aggregates from Tennessee were selected for relative frictional tests. X-ray fluorescence was utilized to quantify the silica dioxide (SiO2) contents, establishing correlations with polish stone value (PSV), micro-Deval (MD) abrasion loss, and surface morphological characteristics of aggregates tested via the aggregate image measurement system. Subsequently, to develop a quick way to measure the SiO2 of RAP, laboratory-produced RAP and field-sampled RAP were compared. Laboratory-produced RAP was fabricated and compared with chemical trichloroethylene (TCE) and a hammer-crushed processing method to accurately measure the SiO2 content for the application of field-sampled RAP. Field pavement friction tests were conducted to correlate the laboratory findings to field measurements. Results show that the coefficients of determination (R2) of SiO2 from raw aggregates with PSV, MD loss, and texture loss are 0.81, 0.60, and 0.78, respectively. Field-sampled RAP washed by TCE three times could provide more accurate SiO2 content compared with hammer crushing. The field pavement friction test demonstrates that pavements with lower SiO2 contents exhibit reduced skid resistance due to texture loss caused by traffic polishing. These findings offer a straightforward method for evaluating pavement friction and selecting RAP with high skid resistance, where higher SiO2 content provides higher friction properties. As a result, this research provides a valuable strategy for the rapid evaluation of aggregates and RAP for skid resistance. [ABSTRACT FROM AUTHOR]

Great efforts have been made in recent years by the scientific community and the asphalt industry in developing sustainable technologies for the production of asphalt mixtures for road paving applications, pursuing the use of ever higher quantities of recycled materials. In this regard, the challenge is to define the optimal formulation of the mixture which allows the various component materials to be synergistically combined without compromising the performance and durability of the asphalt pavement. In such a context, the experimental study described in this paper aimed to provide a contribution to research by investigating sustainable asphalt mixtures containing 50% reclaimed asphalt pavement (RAP) and polymeric compound composed of 100% recycled plastics. A wide set of mixtures was prepared in a laboratory by employing different dosages of polymeric compound added via the hybrid method at various binder contents. For comparison purposes, an additional set of reference asphalt mixtures containing standard polymer-modified binder (PmB) and virgin aggregate without RAP was prepared and tested. The experimentation focused on the main engineering properties of the asphalt mixtures, including their workability, volumetric properties, and mechanical characteristics. The experimental study involved a preliminary trial phase to establish an appropriate laboratory mixing procedure. The results obtained from the experimentation indicated that recycled waste plastics have good potential for use in asphalt mixtures with high contents of RAP, provided that the quantity of added plastics is adequately balanced. [ABSTRACT FROM AUTHOR]

In this study, a novel epoxy-recycling technology, which produces recycled mixtures using epoxy asphalt as binders, was applied to utilise 100% RAP. However, to date, the fatigue properties of epoxy-recycled asphalt mixtures (ERAM) made of 100% RAP remains unknown. The main objective of this paper is to investigate the fatigue performance of epoxy-recycled binders and mixtures. Thus, the linear amplitude sweep (LAS) tests and repeated semi-circular bending (R-SCB) fatigue tests were conducted to evaluate the fatigue resistance of binders and mixtures, respectively. The binder bond strength (BBS) tests were also performed to investigate their adhesive performance. The results show that the epoxy-recycling technology can recover the fatigue properties of ERAM to similar levels or even far superior to conventional virgin mixtures. Compared to SBS modified asphalt, the bonding strengths of epoxy-recycled binders increase by 92.38%, 110.16%, 133.33%, and 210.76% with increasing epoxy proportions. The fatigue lives between LAS tests for binders and R-SCB tests for mixtures show excellent correlations under power functions, and the fatigue performance enhancement of ERAM can be attributed to greater fatigue resistance of binders and better adhesive properties. The findings will provide evidence-based confidence in epoxy-recycling technology, thereby promoting long-life and sustainable pavement construction. [ABSTRACT FROM AUTHOR]

In the recent years, research on the effects of rejuvenation on hot mix asphalt (HMA) with a high amount of RAP (Reclaimed Asphalt Pavement) has intensified. However, the vast majority of scientists focus on the technology of preheated RAP addition (e.g. in the parallel dryer). It was decided to investigate the effect of rejuvenators on asphalt mixtures containing non-preheated RAP (RAP cold addition into the mixer). Different types of rejuvenators were used in the research. The tests were carried out for the binder course and the base course. The optimal amount of cold RAP in the mixtures was determined and based on the initial tests of stiffness modulus and air void content, the amount of rejuvenators was adjusted for later tests. Tests of air void content, stiffness, resistance to water and frost and rutting resistance were carried out in the laboratory. Afterwards tests in the asphalt mixing plant were conducted for the rejuvenator with the best results for the base course. The results obtained confirmed the potential of using rejuvenators for mixtures with cold RAP addition into the mixer. It has been shown that bio-based rejuvenators are suitable for the use in different types of asphalt mixtures. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) reduces energy consumption and enhances economic benefits by recycling road materials, making it an effective approach for the sustainable use of solid waste resources. The performance of reclaimed asphalt pavement is significantly affected not only by the degradation of asphalt binders due to aging but also by the dosage of the rejuvenator used. The master curve of the complex shear modulus is widely recognized as a valuable tool for characterizing the rheological properties of asphalt binders. First, a virgin asphalt binder with a grade of SK70 was subjected to varying degrees of aging, followed by the rejuvenation of the aged asphalt using different dosages of the rejuvenator. Second, frequency sweeps were conducted on the aged and rejuvenated asphalt binders at various temperatures. Complex modulus master curves were constructed, and the CAM model was applied to fit these curves. The viscoelastic properties of asphalt at different aging levels and rejuvenator dosages were then analyzed based on the CAM parameters. Next, by applying a curve-shifting technique based on the least squares method to a reference state, both the time–temperature–aging (TTA) and time–temperature–regenerator (TTR) master curves of the complex modulus were constructed. The relationships between aging shift factors and aging times, as well as between regenerator shift factors and dosages, were established to predict the complex moduli of both aged and rejuvenated asphalt. Finally, the shear stress–strain relationships and material integrity of aged and rejuvenated asphalt were evaluated to assess their fatigue performance. The results indicated that aging significantly increases the complex modulus of asphalt, with TFOT (Thin Film Oven Test) aging having a more pronounced impact than PAV (Pressurized Aging Vessel) aging, resulting in reduced viscous deformation and an increased risk of cracking. Rejuvenator dosage reduces the complex modulus, with a 6% dosage effectively restoring mechanical properties and enhancing low-temperature performance. The TTA master curve demonstrates a strong linear correlation between aging shift factors and time, allowing for accurate predictions of the complex modulus of aged asphalt. Similarly, the TTR master curve reveals a linear relationship between regenerator dosage and shift factor, offering high predictive accuracy for optimizing regenerator dosages in engineering applications. The study further explores how varying levels of aging and rejuvenator dosage affect fatigue life under different strain conditions, uncovering complex behaviors influenced by these aging and regeneration processes. [ABSTRACT FROM AUTHOR]

This study was set out to conduct a life cycle assessment (LCA) to explore the environmental and economic impacts of pavement design alternatives using reclaimed asphalt pavement (RAP) and recycled plastic. 25 design alternative pavement designs were considered for a four-lane 8 km-long highway section. Design mix percentages varied between 0 and 40% of RAP with 10% increments and 0–20% of recycled plastic with 5% increments. The impact was assessed based on estimating utilized energy and water resources, climate change impact in terms of CO 2 equivalent, and air pollution in terms of air acidification, human health particulate (HHP), and photochemical smog. Results show that recycled plastic is superior to RAP in reducing energy consumption and GHG emissions. Both RAP and recycled plastic reduced water consumption. Recycled plastic reduced air acidification, HHP, and smog. RAP also increased HHP substantially, mainly during materials production. It was found that the RAP replacement ratio of 10% yielded the highest value of energy consumption, harmful gases emissions, air acidification, HHP, and Smog. RAP and plastic both reduced costs substantially as recycled material reduced the use of virgin materials and bitumen. In addition, using RAP eliminates the cost of moving RAP to landfills. [ABSTRACT FROM AUTHOR]

This study focuses on assessing the resilient characteristics of a clayey soil modified with a fly ash (FA)-based geopolymer and reclaimed asphalt pavement (RAP) as an unpaved road material. RAP-geopolymer-soil mixtures were designed using the response surface methodology-central composite design with 0–40% RAP and 0–25% FA. The repeated-load California bearing ratio (CBR) testing method was used to determine the recoverable and permanent deformations and then obtain the equivalent (resilient) modulus (Mequ). The Mequ values were used to develop predictive models and determine the optimum soil–RAP–geopolymer mixture. The effects of the load level and soaking period on the stiffness of the optimum mixture were also investigated. The results revealed that the geopolymer binder played a significant role in enhancing the stiffness of the mixtures, with the maximum Mequ obtained at 25% FA and 0% RAP. However, it was determined that RAP has an adverse effect on the stiffness for almost all the studied cases and more significantly for the 40% RAP and 0% FA mixture. The optimal mixture was found to be 25% FA and 30% RAP. The developed model exhibited excellent predictive capability based on ANOVA results. The optimum mixture exhibited stress-softening behavior at an increased load level. No clear trend was observed in the effect of the soaking period on the resilient modulus within the examined soaking period range. Overall, this study agrees with several pavement design guidelines to limit the RAP content used in road applications owing to uncertain adequacy. Additionally, it suggests that the geopolymer binder is an effective stabilizer with excellent environmental and economic potential.

To achieve efficient utilization of reclaimed asphalt pavement (RAP) materials, a bioregenerant (BR) was developed in this research, and waste vegetable oil (WVO), alkylphenol polyoxyethylene ether (APEO), plasticizer [tributyl acetylcitrate (ATBC)] and tackifying resin (FTR) were chosen as components of the regenerant. The composition ratio of BR was designed based on the response surface method (RSM), and the optimal BR dosage and the regeneration effect of BR on the bioregenerated mixture (BRM) with different RAP contents were determined and investigated. Results showed that the optimal composition ratio of BR was found to be WVO-APEO-ATBC-FTR=100:2:23:10. The addition of BR significantly reduced the high-temperature stability and aging resistance of the mixture, but improved its low-temperature cracking resistance and fatigue resistance. Additionally, BR prominently contributed to the improvement for the water stability of the regenerated mixture, and its regeneration effect was found to be similar to that of two commercial regenerants, although excessive BR led to the decline of water stability. Moreover, the high-temperature stability and aging resistance of BRM when mixed with 20%, 30%, and 40% RAP were similar to those of the new asphalt mixture (NAM). At 20%, 30%, and 40% RAP content, both the low-temperature cracking resistance and fatigue resistance of BRM met the requirements. However, when the RAP content exceeded 40%, the water stability of BRM went beyond the specification limit. Taking into account the overall road performance, it is suggested that the optimal BR dosage is 5%–9%, and the maximum RAP content ensuring the road performance of BRM meets the requirements is 40%. These research findings will contribute to addressing the stacking problem of reclaimed asphalt pavement materials and environmental pollution, aligning with green and environmentally friendly sustainable development principles. [ABSTRACT FROM AUTHOR]

The use of high contents of recycled materials in asphalt mixtures has an adverse effect on the low-temperature cracking performance of these mixtures if not accounted for properly due to the high stiffness and poor relaxation properties of the reclaimed asphalt pavement (RAP) binder. This concern has driven some to suggest using recycling agents (RAs) in the asphalt mixture to restore the rheological properties of the RAP binder without compromising the short- and long-term performance of the mixture. However, the relationships between RA type and dosage, virgin and RAP binder characteristics, and low-temperature properties, i.e., creep stiffness and m -value, need to be investigated further to assess the acceptance of RAs. In this study, 26 recycled binder blends from a combination of three virgin binders, four RAP sources, and eight RAs were used to study these relationships. First, the use of a method based on the dynamic shear rheometer to predict low-temperature properties of recycled binder blends successfully is demonstrated. Second, a linear relationship is found to exist between the low-temperature properties and RA dosage of these blends. Third, a parameter based on low-temperature properties is proposed to select an RA that yields a balance in the stiffness and relaxation properties of the recycled binder blends. Fourth, a conceptual framework is proposed to assess the acceptance of RAs based on low-temperature performance-related parameters. [ABSTRACT FROM AUTHOR]

During the production and transport of reclaimed asphalt pavement (RAP), the diffusion of recycled aged asphalt binder and virgin asphalt binder can significantly affect the mechanical properties of the virgin and aged asphalt binder system. Therefore, a thorough understanding of the diffusion behavior of virgin and aged asphalt binder system is essential for the production of RAP. In this study, a diffusion model of the virgin and aged asphalt binder system was established based on the Fick's law to calculate the complex shear modulus (|GT*|) of the system. The calculated |GT*| values were then compared with the measured values (|GD*|) obtained from the dynamic shear rheological (DSR) test. molecular dynamics (MD) simulations were also carried out to investigate the diffusion behavior of the virgin and aged asphalt binder system and to compare the simulated and calculated values of the diffusivity (D). The influence of different asphalt binder layers and saturates, aromatics, resins, and asphaltenes (SARA) on the diffusion behavior of the system was also analyzed. The results show that the |GT*| values calculated by the diffusion model are in good correlation with the |GD*| values measured by the DSR test at different temperatures and times. Furthermore, the diffusivity of virgin asphalt binder was found to be smaller than that of the four individual components, suggesting that the colloid structure and intermolecular interactions of asphalt binder play a crucial role in its diffusion behavior. Practical Applications: Asphalt pavement is a common form of pavement, but it can be seen in life that asphalt pavement often has diseases such as cracks and potholes. The cause of some pavement diseases is the decrease of the performance of asphalt binder in the pavement. Under the action of natural factors, the phenomenon that the performance of asphalt binder gradually changes with time is called asphalt aging. Therefore, if the principle of asphalt aging can be mastered, the influencing factors of asphalt aging can be clarified, and a rejuvenator that can restore the performance of aged asphalt binder to the greatest extent can be designed. It can delay the aging rate of asphalt binder and improve the durability of asphalt pavement, conversely, it can also effectively recycle and renovate old asphalt pavement, reuse waste asphalt concrete, and reduce the waste of resources. This article mainly uses molecular dynamics simulation to achieve the preceding purpose. The result is helpful in providing guidance for the production of RAP in practical application. [ABSTRACT FROM AUTHOR]

This study focuses on assessing the resilient characteristics of a clayey soil modified with a fly ash (FA)-based geopolymer and reclaimed asphalt pavement (RAP) as an unpaved road material. RAP-geopolymer-soil mixtures were designed using the response surface methodology-central composite design with 0–40% RAP and 0–25% FA. The repeated-load California bearing ratio (CBR) testing method was used to determine the recoverable and permanent deformations and then obtain the equivalent (resilient) modulus (M equ). The M equ values were used to develop predictive models and determine the optimum soil–RAP–geopolymer mixture. The effects of the load level and soaking period on the stiffness of the optimum mixture were also investigated. The results revealed that the geopolymer binder played a significant role in enhancing the stiffness of the mixtures, with the maximum M equ obtained at 25% FA and 0% RAP. However, it was determined that RAP has an adverse effect on the stiffness for almost all the studied cases and more significantly for the 40% RAP and 0% FA mixture. The optimal mixture was found to be 25% FA and 30% RAP. The developed model exhibited excellent predictive capability based on ANOVA results. The optimum mixture exhibited stress-softening behavior at an increased load level. No clear trend was observed in the effect of the soaking period on the resilient modulus within the examined soaking period range. Overall, this study agrees with several pavement design guidelines to limit the RAP content used in road applications owing to uncertain adequacy. Additionally, it suggests that the geopolymer binder is an effective stabilizer with excellent environmental and economic potential. [ABSTRACT FROM AUTHOR]

In the production of asphalt mixtures containing reclaimed asphalt pavement (RAP), the traditional heating method has certain limitations, such as partial mobilization, low blending, and secondary aging. These drawbacks result in reduced technical properties of recycled asphalt mixtures, such as the crack resistance, fatigue resistance, and water stability, thereby leading to strict restrictions of RAP content in the recycled asphalt mixtures. To address these issues, microwave induction was used in this study to produce recycled asphalt mixtures. Fluorescence microscopy and molecular dynamics simulation with thermoelectric coupling field were used to examine the viability of increasing the blending efficiency by adding nanometer microwave absorbents. The findings show that microwave induction can be used to increase the blending efficiency of aged and virgin binders and that adding nanoscale microwave absorbents can further increase this efficiency. By incorporating nanoscale SiC at a concentration of 0.5%, the temperature-rising rate of asphalt under microwave heating was improved by up to 31.4%. The self-diffusion coefficient of asphalt incorporating microwave absorbent is dramatically raised and is 2.1 times that of virgin asphalt without microwave absorbent and 4.9 times that of aged asphalt, indicating that microwave absorbent is conducive to the blending of virgin and aged asphalt under microwave action. [ABSTRACT FROM AUTHOR]

Traditionally, the mix design was majorly the trial and error process of optimising aggregate gradation and asphalt content. With the progress of concept and technology, the number of design gyrations (Ndes) has been gradually regarded as another important design variable. This research explored the potential advantage of mixes designed incorporating multiple design parameters. The paper is divided into two parts. Part 1 designed the varied aggregate gradations with different levels of Ndes to evaluate the effect of incorporating the Ndes variable in a traditional process. Part 2 further explored the possible combinations of multiple design parameters, involving binder type, Ndes, RAP addition and aggregate gradation. The result showed that by selecting a suitable level of Ndes, the performance of mixes with different aggregate gradations can be well balanced to a certain extent. Besides, the performance of HMAs may be largely improved and some marginal materials can be reutilised by selecting a suitable combination of multiple design parameters. [ABSTRACT FROM AUTHOR]

This study explores the development of performance-based blending charts for recycled binder blends, considering the rutting and fatigue resistance of recycled binder blends. For developing the blending chart, the nonrecoverable creep compliance Jnr evaluated in the multiple stress creep recovery (MSCR) test and the bitumen fatigue performance parameter Nf estimated from the linear amplitude sweep (LAS) test were utilized. These parameters are recognized for their superior representation of rutting and fatigue performance. Blending charts were initially developed separately for Jnr and Nf , then combined to create a performance-based blending chart that illustrates how Jnr and Nf change with reclaimed asphalt binder in total binder (R/T). The study demonstrates the aforementioned concept for a laboratory-synthesized reclaimed asphalt pavement (RAP) binder when blended separately with two virgin binders (viscosity grades VG10 and VG20). Because viscosity grade VG40 binder is recommended for wearing-course and binder-course mixes for high-volume roads in India, the RAP blends were synthesized targeting the Jnr and Nf values estimated for VG40 binder at 60°C and 25°C, respectively. The performance-based blending charts identify an R/T range where the blend outperforms the target binder in both rutting and fatigue performance. The study revealed that when the softer virgin binder (VG10) was used to rejuvenate RAP properties, the desired R/T range was broader compared with VG20. As the strain level increased from 2.5% to 5%, the desired R/T range narrowed, indicating that the R/T range was influenced by both the type of soft binder and the strain level in the LAS test. This also implied that higher RAP incorporation is advisable in the case of thick pavements when compared with thin layers. [ABSTRACT FROM AUTHOR]

The stabilization of asphalt pavement bases with granular soil and aggregates emulsified with asphalt is a widely used technique in road construction and maintenance. It aims to improve the mechanical properties and durability of the lower pavement layers. Currently, there is no consensus on the most suitable method for designing emulsified granular aggregates with reclaimed asphalt pavement (RAP), as it is very complex. Therefore, the methodology is generally based on compliance with one or more volumetric or mechanical parameters established in the highway regulations for conventional asphalt mixtures, which does not guarantee the optimization and characterization of the recycled mixture in the base course. In this study, granular mixtures were developed, including five with emulsion and one emulsion-free as a control mix. Granular RAP mixes were designed in this study, including five with emulsion and one emulsion-free as a control mix. The five mixes ranged from 1% to 5% emulsion and were characterized by multi-stage triaxial tests with repeated load resilient modulus (RM) and permanent deformation (PD) to evaluate their mechanical behavior. The results showed that the mixes had RM values between 350 and 500 MPa, consistent with literature values. However, they showed similar levels of accumulated deformation to the control mix without RAP emulsion. The sample with 1 % RAP emulsion exhibited a satisfactory RM value and better performance in PD than the control mix (5 mm) and showed accumulated PD values of up to 4 mm. In contrast, the other samples exhibited deformations of up to 6 mm. In this study, the multi-stagge triaxial RM and PD tests were found to be an effective predictive method for characterizing the behavior of RAP materials in base courses, regardless of the types of admixtures contained. Multi-stage resilient modulus and PD tests can be considered as a predictive method for the behavior of milled material in base courses. They were able to provide initial data for interpreting the behavior of ETB mixtures. [ABSTRACT FROM AUTHOR]