Reclaimed Asphalt Pavement Content Research Articles

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.

Performance of High-Dose Reclaimed Asphalt Mixtures (RAPs) in Hot In-Place Recycling Based on Balanced Design.

This study endeavors to employ a balanced design methodology, aiming to equilibrate the resistance to rutting and cracking exhibited by hot in-place recycling asphalt mixtures containing a high dose of reclaimed asphalt pavement (RAP). The primary goal is to ascertain the optimal amount of new binder necessary for practical engineering applications, ensuring a balanced rutting and crack resistance performance of recycled asphalt mixtures. The investigation mainly employed wheel-tracking tests and semi-circular bending tests to assess the rutting and cracking performance of recycled asphalt mixtures with a different dose of RAP (in China, it is common to use RAP with 80% and 90% content as additives for preparing hot in-place recycling asphalt mixtures), and varying quantities of new binders (10%, 20%, and 30% of the binder content in the total RAP added). The results indicated that the addition of new binder reduced the resistance to rutting of the recycling asphalt mixtures but improved their resistance to cracking. Furthermore, for the recycling asphalt mixture with 80% RAP content aged for 5 days, the optimal new binder content is 1.52%, while the mixture with 90% RAP content requires 1.23% of new binder. After 10 days of aging, the optimal new binder content for the recycling asphalt mixture with 80% RAP content is 1.55%, while the mixture with 90% RAP content requires 1.28% of new binder.

On the effect of nano calcium carbonate on the flexibility and tensile-shear cracking resistance of greener WMA asphalt concretes containing RAP contents

Asphalt mixtures are widely used materials for paving roads, however, they need a significant amount of virgin materials, and their preparation process is environmentally unfriendly. In this regard, using less harmful production processes and using recycled materials can be beneficial. In the current study, the cracking resistance parameters (fracture toughness and fracture energy) of warm mix asphalt (WMA) mixtures, prepared with high contents of reclaimed asphalt pavement (RAP) were investigated, while different contents of nano calcium carbonate (NC) were used as a modifier. The cracking resistance studies were done for the full range of mode I/II fracture conditions. From the results, it is seen, that the addition of RAP increases both fracture toughness and fracture energy, regardless of the mode mixity and NC contents (respectively by an average, of 30 % and 20 %). The NC also made the mixture more resistant to cracking, so the enhancement of fracture energy by up to 30 % and the enhancement of fracture toughness by up to 20 % is observed. The NC optimum content was calculated in the range of 2–4 % (in weight of binder), varied based on the considered variables. As a result of increasing the material’s brittleness by adding RAP and NC, the flexibility index showed a decrease. In separate evaluations, the effect of variables on strength parameters was studied statistically, showing that the fracture toughness in mode II, is about 1.2–1.5 times higher than fracture toughness in mode I. Also, theoretical frameworks were used to predict the trend of fracture data, showing the consistency of experimental results and theoretical predictions.

Mechanical Properties and Performance of Mixtures Containing a High Level of Recycled Materials That Are Designed Using Alternative Approaches

Using recycled asphalt material (RAM) in asphalt mixtures is very common among transportation agencies. With the recent development of balanced mix design methods, it is becoming more important to understand how to optimize mixture performance by offsetting the adverse effects of RAM. In this paper, mixtures from three different sources were adjusted according to the availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC) methods. Three control mixtures containing RAM, three mixtures containing no RAM, five mixtures designed according to the AAMD method (two of which had 50% reclaimed asphalt pavement content), and two mixtures adjusted using the COAC-based approach were evaluated. Both asphalt mixture performance tester experiments and index tests were used in this study to evaluate material-level indicators of cracking and rutting resistance. Additionally, pavement performance simulations were carried out using AASHTOWare Pavement ME and FlexPAVETM to assess how the observed material-level differences led to differences in structural-level pavement performance. Both the AAMD and COAC methods improved cracking measures. However, the results suggest that the additional virgin binder added through the COAC method without any adjustments to the aggregate structure can have negative consequences for the rutting performance measures. In addition, the mixture and pavement performance results suggest that the AAMD method is a rational approach for including recycled binder availability in mix design procedures to promote improvements in the cracking performance of mixtures by controlling the volumetric properties and the aggregate structure of the mix without having a detrimental effect on rutting resistance.

Appraisal of reclaimed asphalt pavement as coarse aggregates in cement concrete

This systematic literature review evaluates reclaimed asphalt pavement (RAP) in concrete construction, targeting reduced natural aggregate use and lower construction carbon footprint. It comprehensively covers RAP in concrete, including mechanical properties, durability, test methods, mix design, performance, influencing factors, RAP content, processing, admixtures, curing, and environmental aspects. RAP concrete matches traditional concrete mechanically while increasing sustainability through waste reduction. Durability parameters, like permeability, freeze-thaw resistance, and chloride penetration, suggest long-term structural enhancement. Reliable testing methods and standards are vital for RAP in concrete assessment. The review explores RAP in mix design, considering content, gradation, and processing. Admixtures and additives optimize RAP concrete. Curing and environmental conditions influence RAP concrete performance. Gaps indicate a need for long-term studies, understanding mechanisms, specific environmental exploration, standardized testing, and economic assessment. The study recommends future research directions to guide sustainable construction practices.

Evaluating the Fatigue-Cracking Resistance of North Dakota’s Asphalt Mixtures

Fatigue cracking is a critical pavement distress caused by extreme environmental conditions and heavy repeated cyclic loading. Performance-based design methods that use mechanistic models focus on material performance properties, creating an opportunity to use engineered and recycled materials such as reclaimed asphalt pavement (RAP). The primary goal of this study was to use the simplified viscoelastic continuum damage (S-VECD) model to assess the fatigue behavior of North Dakota’s asphalt mixtures. Eight mixtures typically used in North Dakota were sampled and underwent | E*| testing to determine their linear viscoelastic (LVE) properties. The S-VECD tests were conducted on the same mixtures to determine their damage characteristics. The outputs from the two tests were exported to the FlexMATTM software to obtain their damage characteristic curves, DR failure criterion parameters, and Sapp-index values. CT-index values for the same mixtures were obtained from the North Dakota Department of Transportation (NDDOT). The results revealed that the mixture used for HWY 52, which does not contain RAP, was least susceptible to fatigue cracking. The mixture used for HWY 6, which contains the highest RAP content (25%), had the lowest fatigue resistance, revealing RAP’s stiffening effect on asphalt mixtures. The mixture used for HWY 1, which used the performance grade (PG) 58S-34 binder, had the second-highest fatigue-cracking resistance despite containing 15% RAP, indicating that binder grade affects an asphalt mixture’s fatigue behavior. A relatively low correlation was observed between the CT-index and Sapp-index.

Availability adjusted mix design method as a tool to mitigate the adverse effects of RAP on the performance of asphalt mixtures

The use of high percentages of reclaimed asphalt pavement (RAP) in asphalt mixtures offers economic and environmental advantages. However, state agencies place limits on RAP usage to avoid its indiscriminate use without a full understanding of its long-term performance implications. To achieve a more informed and rational use of higher RAP contents, it is essential to quantify recycled binder availability (RBA) and incorporate it into asphalt mixture design. The current design methods often assume complete RBA, leading to less durable mixtures. Standardized mixture design methods fail to rigorously account for the effects of RBA on the volumetric composition of asphalt mixture. Recently, the availability adjusted mixture design (AAMD) method was developed to address these issues by explicitly considering partial RBA in the interpretation of mixture volumetric properties and accounting for the role of RAP agglomerations on aggregate structure. This study tests the hypothesis that the AAMD method can mitigate the adverse performance consequences of RAP through the control of ‘available’ volumetric and effective binder properties. This was achieved by comparing virgin and RAP mixtures designed with similar ‘available’ volumetric properties according to the AAMD method. Additionally, control mixtures with RAP contents ranging from 20 to 35 percent were compared to AAMD mixtures with similar ‘available’ volumetric properties designed with the same RAP content and with 50 percent RAP. The collective results demonstrate that the AAMD method effectively mitigates negative performance consequences of RAP by controlling the ‘available’ volumetric and effective binder properties.

Effects of rejuvenators and aging conditions on the properties of blended bitumen and the cracking behavior of hot asphalt mixtures with a high RAP content

The utilization of Reclaimed Asphalt Pavement (RAP) in asphalt pavement has obtained global popularity because of its cost-efficiency, technical advantages, and positive environmental influence. However, incorporating RAP requires careful consideration of cracking resistance because of the existence of age hardening of bitumen in RAP. For the mixtures containing high RAP contents, rejuvenators are often applied to enhance the performances of aged bitumen and the cracking of mixtures. This research aims to evaluate the effects of different rejuvenators on the rheological properties of bitumen and the cracking resistance of the mixture under short and long-term aging conditions. To achieve this goal, three rejuvenators - namely, RA1 (petroleum-based), RA2 (waste vegetable oil-based), and RA3 (modified soybean oil-based) were evaluated at contents of 0%, 4%, 12%, and 20%, respectively. The dynamic shear rheometer (DSR) test results show that, under unaged and rolling thin-film oven (RTFO) aging conditions, blended bitumen with RA1 and RA3 have higher G*/sinδ than RA2. Conversely, under pressure aging vessel (PAV) aging conditions, blended bitumen with RA1 and RA3 has lower G*sinδ than that with RA2. Regarding the cracking resistance, the indirect tension asphalt cracking test results show that, under short-term oven aging (STOA) conditions, the mixture using RA2 and RA3 has a higher cracking tolerance index (CTIndex) than the one with RA1. However, under long-term oven aging (LTOA) conditions, the mixture using RA1 has the highest CTIndex value. In addition, the high correlations between G*sinδ with CTIndex and post-peak slope (|m75|) and between the CTIndex and |m75| are observed.

Multi-level performance evaluation of BMD surface mixtures with conventional and high RAP contents: a case study in Virginia

ABSTRACT This study investigated one control and five Balanced Mix Design (BMD) optimised asphalt surface mixtures, four of which had high reclaimed asphalt pavement (RAP) contents (HRAP mixtures), using laboratory performance tests characterised with different levels of complexity. The performance of the evaluated mixtures was assessed based on durability, rutting resistance, and cracking resistance as emphasized by BMD. The study explored the ranking of a single index and correlations among various indices. Assisted by 3-Dimensional and ternary plots, this study also proposed a novel composite performance index [CPI] that combines major indices (durability, cracking, and rutting) to evaluate the performance of BMD optimised mixtures. The results revealed discrepancies between basic/intermediate performance test results and advanced performance test results. The comparisons conducted also underscored the beneficial impacts derived from using softer binders and/or recycling agents in HRAP mixtures. Furthermore, the findings indicated that the BMD approach can serve as an effective framework for designing asphalt mixtures that simultaneously enhance both fatigue and rutting performance. Moreover, the study revealed HRAP BMD surface mixtures can exhibit superior overall performance when compared to conventionally designed control mixtures.

Uncertainty analysis for the dynamic modulus of recycled asphalt mixtures using unclassified fractionated RAP materials

The use of unclassified reclaimed asphalt pavement (RAP) is limited due to concerns about raw material variability, impacting RAP mixture performance consistency. Space constraints lead to aggregating recycled materials from various projects into "unclassified RAP," hindering its potential benefits. The evaluation of uncertainties, particularly in dynamic modulus |E*|, is crucial for assessing performance and reliability in asphalt mixtures containing unclassified RAP. In this research, A systematic approach for calculating the coarse and fine RAP ratios based on unclassified RAP content, along with regulated processing and fractionation meeting standards was implemented. Then, a probabilistic model was established, utilizing the sigmoidal function, to analyze the uncertainty in |E*| as a function of the reduced frequency for asphalt mixtures with varying unclassified RAP contents (0%, 15%, 25%, and 45%). The findings revealed that |E*| uncertainty was minimal at low temperatures, reasonable at service temperatures, and critical (COV > 30%) at high temperatures for standard and RAP mixtures. Importantly, increasing unclassified RAP content doesn't worsen |E*| uncertainty. Mixes with high unclassified RAP content showed similar or lower COV values across analyzed frequencies. The proposed approach can reduce COV values in high unclassified RAP content mixes, offering a practical solution to leverage these materials' benefits.

Influence of Petroleum-Based and Bio-Derived Recycling Agents on High-RAP Asphalt Mixtures Performance

Reclaimed asphalt pavement (RAP) has been utilized as a potential partial substitute for virgin asphalt binder in asphalt mixtures. However, a primary concern with increasing RAP content in asphalt mixtures is the cracking potential, attributed to the aged RAP asphalt binder (RAP-binder). To address this, the use of petroleum-based and bio-derived recycling agents (RAs) in enhancing the cracking resistance of high-RAP asphalt mixtures has been explored. The objective of this study is to ascertain the effectiveness of six RAs in mitigating cracking in high-RAP asphalt mixtures. The RAs considered include petroleum-crude-oil-derived aromatic oil, soy oil, and four types of tall-oil-derived phytosterol (industrial by-product, intermediate, purified, and fatty acid-based). The RAs’ dosages were optimized, based on RAP-binder and unmodified asphalt binder properties, to produce target PG 70-22 asphalt binder when incorporated in asphalt mixtures containing 30% RAP. To assess the engineering performance of these 30%-RAP asphalt mixtures for each RA, a conventional asphalt mixture incorporating styrene-butadiene-styrene (SBS)-modified PG 70-22 asphalt binder without RAP or RAs was benchmarked for comparison. Mechanical tests performed included Hamburg wheel-track testing (HWTT), intermediate-temperature fracture tests (semi-circular bend, Illinois flexibility index, and IDEAL cracking tolerance), and thermal stress-restrained specimen tensile strength test to evaluate permanent deformation, intermediate-temperature cracking resistance, and low-temperature cracking resistance, respectively. Results showed that petroleum-crude-oil-derived aromatic oil and tall-oil-derived fatty-acid-based oil RAs were able to rejuvenate RAP-binder as measured by the cracking tests performed. Further, the use of these RAs did not adversely impact the asphalt mixtures’ permanent deformation performance.

Effect of Curing Temperature on the Shrinkage of Concrete Containing Reclaimed Asphalt Pavement: Experimental and Numerical Study

The aim of this research is to determine the effect of curing temperatures (20°C, 40°C, and 60°C) and incorporation rates of reclaimed asphalt pavement (RAP) on the mechanical properties and shrinkage of concrete made with reclaimed asphalt pavement (RAP-C). Five mixes were produced for this study: one with natural coarse aggregate and four with four replacement ratios of coarse RAP (25%, 50%, 75%, and 100%). The results show that the use of RAP reduces the workability and adversely affects the mechanical performance of RAP-C. Moreover, this study found that the total shrinkage increases with coarse RAP content. However, the total shrinkage of RAP-C decreases as the curing temperature increases: for concrete made with 100% RAP, a 20% reduction in total shrinkage was observed at 60°C compared to conventional concrete at 180 days. In addition, to predict the total shrinkage of RAP-C, finite element analysis using ANSYS© software based on the maturity approach and the two-phase serial model is used. The numerical results are in close agreement with the experimental data.

Quantifying the agglomeration effect of reclaimed asphalt pavement on performance of recycled hot mix asphalt

The utilization of reclaimed asphalt pavement (RAP) is becoming widespread in asphalt pavement industry. However, the agglomeration of RAP might exist during asphalt mixture production, which can affect the performance of asphalt mixtures. This study aimed to develop an innovative RAP agglomeration quantification method and investigate the agglomeration effect on performance of recycled hot mix asphalt (RHMA). The inherent agglomeration rate (IAR) and relative agglomeration rate (RAR) were defined and quantified by using the gradation curves. The RAP agglomeration was further determined under different mixing conditions including aggregate size, mixing time, temperature, etc. The influence of RAP agglomeration on hot mix asphalt mixture (HMA) was characterized through wheel rutting, low-temperature cracking, and moisture resistance testing. Results showed that RAP agglomeration do exist during asphalt mixture production, especially for high RAP content. The gradation curves from screening test proved to be an effective approach for RAP agglomeration quantification. The agglomeration rates of No.1, No.2, and No.3 RAP aggregates could be reduced by 5.7, 6.5 and 39.8 % under appropriate mixing conditions. But the fine RAP aggregates were easily re-agglomerated to form the coarse RAP aggregates. The ratio of 150 % between virgin coarse aggregate and RAP aggregate could avoid re-agglomeration issue for No.2 and No.3 RAP aggregates. Based on the rutting, low-temperature cracking, and moisture resistance tests, the impact of agglomeration phenomenon on the performance of plant RHMA with containing 100 % RAP was more than that with containing 50 % RAP.

The Early Performance Development of Hot In-Place Recycled Asphalt Mixture

With increasing societal attention being directed to resource and environment problems, the research focus on high reclaimed asphalt content mixtures has become pertinent. The degree of asphalt fusion in the thermal regeneration process of a high RAP content reclaimed asphalt mixture has a great influence on its performance. In order to explore the development process of hot in-place recycling mixture performance along with internal asphalt fusion, this study conducted research on a geothermal regeneration mixture with 80% RAP content. Dynamic shear rheology (DSR), infrared spectroscopy, and scanning electron microscopy were used to investigate the fusion of recycled mixture under different placement times (1 day, 4 days, and 7 days), and the road performance and fatigue life of the recycled mixture under different placement times were then studied. The results showed that the fusion degree of old asphalt and new asphalt in a recycled asphalt mixture reached 100%, and gradually increased with the extension of placement time. With the increase in placement time, the high temperature performance of the regenerated mixture gradually decreased, the water stability gradually increased, and the low-temperature performance and fatigue life significantly increased from 1 day to 7 days, by 19% and 32%, respectively.

Measurement of the Promoting Effect of Complex Conditions on the Adhesion Development in Curing Process of Cold Recycling Mixture with Emulsified Asphalt

The curing process of cold recycling mixture with emulsified asphalt is a process of emulsion breaking, water evaporation, and cement hydration, resulting in adhesion development and strength formation. There are many factors that affect this process, including curing temperature, curing time, reclaimed asphalt pavement (RAP) contents, and cement contents. However, the evaluation of the promoting effect of each factor is still not quite clear. Hence, in this paper, the curing temperature, curing time, and RAP contents were discussed to find out the dominating factor in this process. The development of moisture loss and indirect tensile strength (ITS) was measured and analyzed through establishing prediction models between them and curing time. Besides, the functional relationship between moisture loss and ITS was also analyzed to evaluate the promoting effect of each factor. The results showed that the curing temperature has a certain impact on the development of moisture loss and ITS and an increase in curing temperature would accelerate the reaction rate, while RAP contents can hardly affect this process. Through functional relationship between moisture loss and ITS, it was found that the development of early strength and adhesion was dominated by ITS despite the increase of curing temperature and RAP contents. Expanding the hydration effect of cement could promote the curing process. However, this dominating role weakened at higher temperature and moisture loss should be treated more carefully.

Optimizing Rural Pavements with SBS-Modified Asphalt Binders and Petroleum Resin

This study addresses the imperative for enhancing asphalt mixtures tailored for rural pavements, focusing on optimizing RAP mixtures with styrene–butadiene–styrene (SBS)-modified asphalt binders incorporating petroleum resin and oil. Through systematic investigation, the study examines the impact of varying RAP content (25% and 50%) and two SBS-modified asphalt binder types (Type 1 and Type 2) on mechanical properties and sustainability. Laboratory tests reveal that the mix of 25% RAP + 75% Type 1 exhibits exceptional flexibility, evidenced by a high ductility value of 880 mm at 25 °C, enhancing pavement resilience. Conversely, the 50% RAP + 50% Type 2 mixture displays vulnerability to fatigue cracking, while 25% RAP + 75% Type 1 demonstrates superior resistance, with a fatigue vulnerability value of 1524 kPa. The Hamburg Wheel Tracking test highlights the influence of RAP content on rut depth, with the mix of 50% RAP + 50% Type 1 achieving the lowest rutting at 3.9 mm. Overlay test results show the mix of 25% RAP + 75% Type 2’s resilience, with the lowest load reduction at 64.5%, while the mix of 50% RAP + 50% Type 1 exhibits substantial load reduction at 82.1%. Field tests unveil differences in pavement bearing capacities, with the mix of 25% RAP + 75% Type 2 demonstrating a remarkable elastic modulus of 58.5 MPa, indicating heightened bearing capacity. The investigation underscores the significant role of SBS-modified asphalt binders with incorporated petroleum resin and oil in enhancing fatigue resistance for sustainable rural pavements.

The effect of RAP content on fatigue damage property of hot reclaimed asphalt mixtures.

The fatigue property of the recycled mixture affects the structural design of recycled pavement. In order to explore the effect of different reclaimed asphalt pavement (RAP) content on the fatigue properties of recycled mixtures, the fatigue properties of recycled mixtures were analyzed through an indoor fatigue test and finite element numerical simulation. Based on the phenomenological method and the dissipated energy theory, the fatigue properties of recycled mixtures with different RAP contents were analyzed and the fatigue damage of the mixtures were also studies under various strain levels. Based on the finite element numerical model of fatigue damage, the stress distribution and internal damage field distribution of trabecular specimens under different temperatures, strain levels and RAP contents were analyzed. The results showed that the anti-fatigue level of the mixture decreased as the RAP content was increased. The relative change rate of dissipated energy for different types of mixtures showed a two-stage change rule with the change of load times, that is, the value is large and decreasing, and the value is small and stable. The correlation between the plateau value (PV) and the fatigue life was established under the double logarithm coordinates, which could better analyze the influence law of the RAP content on the fatigue performance of the recycled mixture. Under different temperatures, strain levels, and RAP contents, the stress at the bottom of trabecular specimen and the overall damage field were mainly generated at the upper part under compressive stress and the bottom under tensile stress, and the damage field distribution area accounted for a small part of the whole specimen. According to the test results and fatigue damage distribution, it is recommended that the content of recycled aggregate in recycled asphalt mixtures be less than 30% to ensure good performance. The research results have important practical significance for the improvement of fatigue performance and engineering application of recycled mixtures.

Experimental evaluation of fatigue performance of recycled asphalt mixture using refined separation recycled aggregates

In order to improve the utilization of reclaimed asphalt pavement (RAP) in recycled asphalt mixtures (RAMs), RAP was firstly separated into recycled mortar and coarse refined separation recycled aggregates (CRSRAs) with different particle sizes based on a laboratory refined separation method. Meanwhile, the process parameters for RAP separation were optimized by using the orthogonal test method. The related properties of the aggregates before and after refined separation, including residual bitumen binder content, particle agglomeration, angularity, and sphericity, were characterized. The cumulative distribution of sphericity of CRSRAs was fitted with the Weibull function. Asphalt mixtures with 0, 30%, and 50% RAP content were prepared by the Marshall design method. Moreover, the indirect tensile dynamic modulus and fatigue life of these asphalt mixtures after different water immersion periods were evaluated. The results showed that the CRSRAs had a residual binder content less than 1.0% and fewer pseudo particles after refined separation. Furthermore, a bitumen-rich mortar with a particle size less than 2.36 mm and a bitumen content of 10–14% was obtained. Angularity and Weibull fitting results verified that refined separation could homogenize RAP and obtain CRSRAs with a low variability, which helps to prepare better RAMs with high RAP content. RAMs prepared with CRSRAs exhibit superior fatigue performance compared to the traditional RAMs. Their fatigue life was less sensitive to stress changes and fluctuated little with the increasing water immersion time.

Effect of RAP's preheating temperature on the secondary aging and performance of recycled asphalt mixtures containing high RAP content

Plant-mixed hot recycling technology is widely used. Due to concerns about the road performance of recycled asphalt mixtures with high RAP content, the content of RAP is strictly limited, which has negative impact on ecological and economic benefits. Low preheating temperature of RAP material is an important reason for reduced performance of recycled asphalt mixtures containing high RAP content. At the same time, excessive preheating temperature of RAP materials can cause secondary aging of asphalt in RAP. This study regarded the preheating temperature as a variable. Rheological and spectroscopic tests such as DSR and BBR, and FTIR tests were conducted to investigate the effect of RAP preheating temperature on the secondary aging of RAP. Afterwards, the influence of raising preheating temperature of RAP on the performance of recycled asphalt mixtures was explored synthetically. When the preheating temperature is below 160 ºC, there is no significant secondary aging of aged asphalt in RAP. However, when the preheating temperature increases to 180 ºC, the rheological properties of aged asphalt undergo certain changes. Increasing the preheating temperature of RAP can significantly improve the low-temperature crack resistance and fatigue performance of recycled asphalt mixtures by reason of maximally activating the aged asphalt. Increasing the preheating temperature of RAP does not weaken the high-temperature anti-rutting performance of recycled asphalt mixture. It is recommended to control the preheating temperature of RAP at 160 ºC in the design and production process of hot recycled asphalt mixtures.