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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]

In the recent times, rejuvenators have been investigated as a potential solution to incorporate higher amounts of recycled asphalt (RA) in hot-mix asphalt (HMA). In this study, waste cooking oil (WCO) was used as rejuvenator to assess the performance of RA mixtures. A method was proposed to optimize WCO content in HMA with high RA content (>45%), balancing the performance in the high and intermediate temperatures. The optimized mixtures with high RA content depicted rut depth and cracking properties similar to HMA. Simultaneously, the recycled mixtures utilizing WCO dosages derived from a blending equation exhibited pronounced rutting, implying that the blending equations yielded WCO dosages that exceeded the necessary dosages. A life cycle assessment (LCA) study considering a cradle-to-gate approach indicated that incorporating 45%, 60%, and 75% RA would decrease total embodied energy (TEE) by 25.08%, 33.30%, and 41.17% compared with HMA. Further, a sensitivity study with distance as the parameter indicated that the permissible distance of RA source for 45%, 60%, and 75% was 500, 300, and 300 km, beyond which RA mixtures showed higher TEE than HMA. Practical Applications: The incorporation of reclaimed asphalt pavements (RAP) using waste cooking oil as a rejuvenator presents significant practical implications for the asphalt industry and sustainability initiatives. By enabling the use of higher RAP content while maintaining the performance of traditional mixtures, this research offers a more environmentally friendly and cost-effective approach to road construction. Moreover, the life cycle assessment findings reveal substantial reductions in environmental impacts when including different RAP proportions, making a strong case for improved environmental sustainability. The sensitivity analysis regarding the distance between RAP sources and construction sites provides valuable insights for location-based decision-making, ensuring that the benefits of RAP utilization remain maximized. In summary, the potential application of the study emphasizes a greener and durable road infrastructure, with a focus on increasing RAP content using waste cooking oil as a rejuvenator in asphalt mixtures. [ABSTRACT FROM AUTHOR]

The cold recycling technology of asphalt pavement has great economic benefits, is friendly to the environment and has a good development prospect. But the reclaimed asphalt pavement (RAP) is used as the "black aggregate," and the aged asphalt has not been fully utilized. Therefore, activating and reusing the aged asphalt in RAP is one of the key problems to be solved. By using artificially aged asphalt instead of naturally aged asphalt, this work reports a new technique for activating asphalt of RAP by functional oil emulsion. The functional oil emulsion was prepared by phase inversion method, and the asphalt regeneration effects were studied in detail. The optimum results showed that the solid content of the functional oil emulsion was 50% and the average particle size was 2.17 μm. The storage stability of 1 day and 5 days were 2.2% and 4.8% respectively, and the demulsification time at 20 °C and 40 °C were 2 hours and 1 hour respectively. By studying the penetration, ductility and softening point of recycled asphalt under different dosages of functional oil emulsion, it is found that the parameters of the recycled asphalt recover to more than 94% at 12% content of functional oil emulsion. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) contains significant amounts of valuable materials, which in new construction in the pavement industry contributes to sustainable development and promoting a circular economy. However, the use of RAP presents challenges. The most critical RAP challenge is cracking at low and medium temperatures. Therefore, it is necessary to use a robust and available tool to evaluate the performance of RAP cracking. The semicircular bending (SCB) test is considered an appropriate and helpful option to describe the cracking behavior of asphalt mixtures. The available standards for the test mentioned above are compiled based on samples with a diameter of 150 mm. However, the equipment to construct 150 mm cylindrical samples cannot be accessed in different parts of the world. Thus, the Marshall compactor was utilized to build SCB samples and examine RAP cracking resistance. Three different percentages of RAP, 0%, 50%, and 100%, were applied to make the samples. In addition, three different rejuvenates, waste engine oil, oleic acid (OA), and vacuum bottom (VB), were used. Each of the rejuvenators was added to the samples in four different percentages. Then recycled high-density polyethylene was first used individually, then combined with rejuvenators, and used at four different rates, 0%, 3%, 5%, and 7%. In the next step, the SCB test was performed at two temperatures, −12°C and 25°C. Next, fracture characteristics at low and medium temperatures were calculated using indices such as fracture toughness, fracture energy (Gf), crack resistance index (CRI), balanced crack index (BCI), and toughness index (TI). Then the results were compared with previous studies based on standard samples. Results indicate that VB at 25°C and OA at −12°C perform best. The BCI was observed to have increased by 41% at 25°C for the sample containing VB, while the CRI showed a significant increase of 62% at −12°C for the sample containing OA. Furthermore, the simultaneous use of OA and polymer had the most significant effect on resistance to crack. So, the crack resistance index improved by more than 54% at −12°C temperature. Finally, statistical analyses were performed, such as coefficient of variation, analysis of variance, correlation, and Tukey. Based on the results, utilizing the Marshall compactor to perform the SCB test exhibited reasonable accuracy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The use of warm-mix recycling technology can reduce the mixing temperature and the secondary aging of binders in reclaimed asphalt pavement (RAP), which is one of the effective ways to recycle high-content RAP. In this study, the penetration, softening point, ductility, and viscosity were used to characterize the conventional physical properties of aged asphalt after regenerating, while a dynamic shear rheometer (DSR), force ductility tester (FDT), and atomic force microscope (AFM) were used to evaluate the rheological performance and micro-morphology of aged asphalt incorporating a new bio-based warm-mix rejuvenator (BWR) and a commercial warm-mix rejuvenator (ZJ-WR). The regeneration mechanism of warm-mix rejuvenators on aged asphalt was analyzed by Fourier transform infrared spectroscopy (FTIR). The results show that the new bio-based warm-mix rejuvenator can restore the conventional physical properties, low-temperature performance, and micro-morphology of aged asphalt with an appropriate dosage, but it has a negative effect on high-temperature performance. In comparison with 2D area parameters, 3D roughness parameters were more accurate in evaluating the variation in micro-morphology of aged asphalt after regeneration. The FTIR analysis results indicate that both the new bio-based warm-mix rejuvenator and the commercial warm-mix rejuvenator regenerate aged asphalt by physical action, and AS=O and AC-H values are more reasonable than the AC=O value for the restoration evaluation of aged asphalt. And the new bio-based warm-mix rejuvenator has a better regeneration effect on the performance and micro-morphology of aged asphalt than the commercial warm-mix rejuvenator. [ABSTRACT FROM AUTHOR]

To study the composition and migration of agglomerate in reclaimed asphalt pavement (RAP), two different RAPs were selected, and the aging performance of RAPs was evaluated. Then, the RAPs were sieved into a single particle size from 13.2 to 0.075 mm, and hot-mix and extraction tests were carried out on the RAPs with single particle sizes. Through the comparative analysis of gradations of the hot mixing and extraction of RAPs with single particle sizes, the composition and its migration rule of agglomerates of RAPs were analyzed. The thickness of gradation (TG), thickness of gradation ratio (TGR), degree of separation (DS), and degree of separation ratio (DSR) were proposed to evaluate the fragmentation characteristics of RAP agglomerates with single particle sizes. According to the DS index, the grading standard of RAP agglomerates was determined. The results show that the agglomerate of RAP at each particle size is mainly composed of the mineral aggregate of the initial particle size of RAP, the aggregate with one gradation lower than the initial particle size, and other aggregates with smaller and finer content. During the hot mixing, the RAP with the single particle size larger than 2.36 mm mainly undergoes old agglomerate fragmentation, whereas RAP with the single particle size ≤2.36 mm will not only break into small particles, but also integrate new agglomerates. The RAP agglomerates can be divided into strongly bound agglomerates and weakly bound agglomerates according to whether they will be broken and separated during hot mixing. With the decrease of particle size of RAP, the proportion of strongly bound agglomerates gradually rises, whereas the proportion of weakly bound agglomerates declines. [ABSTRACT FROM AUTHOR]

In this investigation, four types of sands as alternatives to river sand, namely, crushed sand (CS), marine sand, fine recycled concrete aggregate (FRCA), and fine reclaimed asphalt pavement (FRAP), were studied for their potential for cement-concrete pavement applications. Initially, the physicochemical and morphological characteristics of these sands were understood and later linked to the hydration kinetics and the behavior of cement-mortar systems in both the fresh and hardened states. Due to their evenly graded particle size distribution, CS and FRCA exhibited higher packing densities despite having more gradient angularity, whereas the interlocking capacity of FRAP was found to be affected by the agglomerated particles. Morphology, fineness modulus, and chemical composition of the sands were observed to be the dominating parameters affecting the hydration kinetics and thus the performance of the mortar mixes. Improving these parameters, especially the grain size distribution, could help in enhancing the potential of these sands for pavement applications. [ABSTRACT FROM AUTHOR]

A compound warm-mix asphalt (WMA) technology, surfactant-foamed asphalt (SFA), was proposed to promote warm-mix reclaimed asphalt pavement technology and provide engineering and environmental benefits through nonrenewable materials recycling, cost saving, and energy and emissions reduction. The blending efficiency is critical for the design of SFA warm-mix reclaimed asphalt pavement (SFA-WMRAP) incorporating higher levels of RAP. This study investigated the blending efficiency of virgin and aged asphalt in SFA-WMRAP containing high RAP content. First, the effects of foaming temperature and foaming-surfactant additive dosage on the foaming characteristics and rheological properties of SFA were investigated, and the optimal foaming conditions were determined. Next, an atomic force microscope (AFM) test and fluorescence microscopy (FM) test were used to quantify its blending efficiency after using the stage extraction method. Results indicated that SFA under optimal foaming temperature and surfactant content achieved better workability, rutting resistance, and fatigue resistance. SFA-WMRAP with high RAP content showed a similar blending efficiency compared with the hot-mix process by using the gray mean value as an evaluating index, exhibiting great potential to promote WMRAP for incorporating high contents of RAP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zinc leached in higher concentration than other metals in all asphalt mixtures. • The main source of zinc may be the aggregates. • All metal concentrations would not exceed the drinking water limit. There are concerns about the potential toxicity of bitumen and recycled materials such as reclaimed asphalt pavements from end-of-life roads and crumb rubber from scrap tires used in asphalt mixtures because they contain metals that may be released into the groundwater. This study investigated the potential metal leaching of laboratory-prepared asphalt mixtures modified with polymer coated rubber (PCR) with wet and dry technology, devulcanized rubber (DVR), compared to an unmodified control mixture and a blend modified with a synthetic polymer (SBS). The objectives were to i) quantify concentrations of metals released, ii) calculate the flux rate, the cumulative mass release, and the assessment ratio for each metal, iii) verify if the metals exceeded the EPA drinking water limit, and, finally, iv) assess the source of metals release. Zinc had the highest concentration among all metals and was present in eluates from all mixtures. The cumulative zinc concentration from DVR mixture was 41% and 34% higher than the control and SBS mixtures, respectively. For PCR wet, the cumulative zinc concentration was 9% higher than the control blend and 1% lower than the SBS mix. The assessment ratio indicated that all metal concentrations would not exceed the drinking water limit, except for zinc, for which further evaluations were required. The main source of zinc may derive from aggregates. This work showed that crumb rubber might not be the only source of metal leaching, and its use in asphalt pavements does not cause a metal leaching higher than other materials. [ABSTRACT FROM AUTHOR]

In the context of green and low-carbon development, energy saving, and emission reduction, hot recycling technology (RT) has been researched, which is divided into hot central plant RT and hot in-place RT. However, due to the aged asphalt binders, the shortcomings of hot recycled asphalt mixtures have become apparent, as in comparison to new asphalt mixtures, their resistance to cracking was inferior and the cracking resistance deteriorated more rapidly. Therefore, it was very necessary to focus on the improvement of crack resistance of hot recycled asphalt mixtures. Basalt fiber has been proved to be able to effectively improve the comprehensive road performance of new asphalt mixtures. Therefore, this paper introduced basalt fiber to hot central plant recycled and hot in-place recycled asphalt mixtures, in order to improve the crack resistance of asphalt as a new type of fiber stabilizer. Firstly, six types of SMA-13 fiber asphalt mixtures were designed and prepared, i.e., hot mixtures with basalt fiber or lignin fiber, hot central plant recycled mixtures with basalt fiber or lignin fiber, and hot in-place recycled mixtures with basalt fiber or lignin fiber. Secondly, the trabecular bending test, low-temperature creep test, semi-circular bending test, and IDEAL-CT were used to comparatively study the changing patterns of low and intermediate temperature cracking resistance of hot recycled mixtures with conventional lignin fibers or basalt fibers. Finally, Pearson's correlation coefficient was used to analyze the correlation of the different cracking resistance indicators. The results show that the low and intermediate temperature cracking resistance of hot central plant recycled mixtures increased by 45.6% (dissipative energy ratio, Wd/Ws) and 74.8% (flexibility index, FI), respectively. And the corresponding cracking resistance of hot in-place recycled mixture increased by 105.4% (Wd/Ws) and 55.7% (FI). The trabecular bending test was more suitable for testing the low-temperature cracking resistance of hot recycled asphalt mixtures, while the IDEAL-CT was more suitable for testing the intermediate-temperature cracking resistance. The results can provide useful references for the utilization of basalt fiber in the hot recycling of SMA-13 asphalt mixtures. [ABSTRACT FROM AUTHOR]

Over 50 MioT of Waste Cooking Oil (WCO) was collected worldwide in 2020 from domestic and industrial activities, constituting a potential hazard for both water and land environments, and requiring appropriate disposal management strategies. In line with the principles of circular economy and eco-design, in this paper an innovative methodology for the valorisation of WCO as a rejuvenating agent for bitumen 50/70 coming from Reclaimed Asphalt Pavement (RAP) is reported. In particular, WCO or hydrolysed WCO (HWCO) was modified by transesterification or amidation reactions to achieve various WCO esters and amides. All samples were characterised by nuclear magnetic resonance, melting, and boiling point. Since rejuvenating agents for RAP Cold Mix Asphalt require a melting point ≤0 °C, only WCO esters could further be tested. Efficiency of WCO esters was assessed by means of the Asphaltenes Dispersant Test and the Heithaus Parameter. In particular, bitumen blends containing 25 wt% of WCO modified with 2-phenylethyl alcohol, showed high dispersing capacity in n-heptane even after a week, compared to bitumen alone (1 h). Additionally, the Heithaus Parameter of this bitumen blend was almost three times higher than bitumen alone, further demonstrating beneficial effects deriving from the use of WCO esters as rejuvenating agents. [ABSTRACT FROM AUTHOR]

Cement mortar mixes were prepared to test the suitability of fine reclaimed asphalt pavement (FRAP) aggregates as a replacement for natural fine aggregates (NFA). With different amounts of NFA (25%, 50%, 75% and 100% by weight) replaced with FRAP aggregates, the mechanical qualities of the mortar mix deteriorated. To counteract this, jarosite – a waste from the zinc industry – was used as a partial replacement for cement (replacements of 5%, 10% and 15%). The jarosite improved the microstructural, mechanical and shrinkage properties. For example, compared with the control mix (100% NFA), the mix containing 25% FRAP aggregates showed a 5.5% reduction in hardened density and a 14% reduction in compressive strength. With the addition of 10% jarosite, there was an increase of 4.85% in hardened density and 7% in compressive strength with respect to the mix containing 25% FRAP aggregates. It is thus suggested that 10% jarosite is used when FRAP aggregates are used to make cement mortar mixes. A cost analysis was also performed. The findings of this work are expected to inspire rational mix design recommendations for mortar mixes including FRAP aggregates, as well as bringing environmental and economic benefits by reducing carbon dioxide footprints. [ABSTRACT FROM AUTHOR]

In the context of ongoing rapid industrialization, the increasing deposition of industrial waste has arisen as a persistent global challenge, necessitating immediate attention and subsequent implementation of sustainable remedies. This study convenes on the efficacy of industrial wastes, namely fly ash and ground granulated blast furnace slag, as geopolymer concrete synthesizers in conjunction with the incorporation of reclaimed asphalt pavement (RAP) aggregates as a replacement for natural coarse aggregates varying over 25% to 100%. Under 7 days of ambient curing, employing 14M NaOH and a 50% RAP replacement, the mix achieved significant strengths of 41.80 MPa in compression and 4.72 MPa in flexure, affirming its suitability for pavement quality concrete (PQC). Through this study, the phenomenon of efflorescence could also be explored, which was particularly significant during the winter seasons. Furthermore, the declining coefficient of determination (R2) with the rise in RAP, observed in the correlation between compressive strength and ultrasonic pulse velocity (USPV), likely signified increased variability in the mixture at higher replacement levels. Assessment of long-term performance in terms of resistance to surface abrasion established the mix as durable, depicting minimal depth of wear (0.081 mm). Furthermore, results of the rapid chloride penetration test (RCPT) demonstrated that the presence of adhered asphalt in RAP aggregates reduces porosity and enhances resistance. Microstructural study was additionally conducted to comprehend the importance of adhered asphalt in impeding crack propagation. ANOVA established a highly significant relationship between the interaction of curing age and RAP fractions with the strength characteristics of the mix. [ABSTRACT FROM AUTHOR]

Potholes are one of the common diseases of asphalt pavements. Cold patching asphalt mixtures (CPAM) are a common material for pothole repair. Reclaimed asphalt pavement (RAP) is a high-potential sustainable material that is commonly used in pavement construction. The aim of this study is to address the balance between performance improvement and cost reduction in CPAM. To achieve this objective, the CPAM was prepared with four different contents of cutback and 100% RAP (RAP-CPAM) and its performances were evaluated by laboratory tests. First, Fourier transform infrared spectroscopy (FTIR) test and scanning electron microscope (SEM) technique were used to analyze the diffusion mechanism between the cutback and the artificial aged binder. Then, the rationality of the cutback content was preliminary estimated by the mixing test and the draindown test. Finally, the adhesion performance, cohesion performance, strength, and resistance to water damage of RAP-CPAM were characterized through laboratory tests. From the FTIR test, the carbonyl index of aged asphalt layer decreased compared to that of the artificial aged binder as the storage time increased. Simultaneously, SEM imaging of the artificial aged binder showed less fractured surfaces after storage. The results of FTIR and SEM tests indicate that the cutback and the artificial aged binder were diffused. It was found that 1.6% content of cutback was slightly lower for RAP-CPAM, and 2.8% was not excessive. Boiling test results show that RAP-CPAM had good adhesion performance. Rolling screen test, Marshall stability test, and immersion Marshall test results reveal that RAP-CPAM had good cohesion performance, strength, and resistance to water damage. Based on the performance evaluation, the optimal content of cutback in RAP-CPAM was determined as about 2.4%–2.8%. In conclusion, the cutback and the RAP binder were successfully diffused, thereby ensuring good performances of RAP-CPAM. [ABSTRACT FROM AUTHOR]

The use of sustainable materials in road construction has been gaining popularity to provide a better future for the next generations. This study investigates the possible use of two common sustainable road construction materials, recycled asphalt pavement (RAP) and recycled tire rubber (RTR), for pavement maintenance applications. Mixtures were produced either with combined RAP and RTRs or 100% RAP with petroleum-based (RAP-A) and bio-based (RAP-B) rejuvenating oils. Because pavement maintenance applications such as pothole patching have traditionally been performed with cold mixtures (CM), a typical cold patching mixture was also investigated along with six hot asphalt mixtures. RTR mixtures were produced using different rubber modification technologies. They were manufactured using crumb rubber wet (WET), crumb rubber dry (DRY), devulcanized rubber (DEV), and crumb rubber terminal blend (TB) technologies. Each RTR-modified mixture included 40% RAP and approximately 12% rubber content by weight of the binder. The performance of the mixtures was compared using dynamic modus (DM) testing for linear viscoelastic characterization, flow number (FN) testing for rutting potential, and tensile strength ratio (TSR) testing for moisture susceptibility. The cost-effectiveness of different mixtures was performed using the life cycle cost analyses (LCCA) approach for bituminous materials. The results showed that any recycled hot-mix asphalt outperformed the CM. The 100% hot RAP mixture with petroleum-based rejuvenator performed as well as any combined RTR-RAP mixtures, and it became the most cost-effective alternative for pavement maintenance applications. [ABSTRACT FROM AUTHOR]

The utilization of reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) in road infrastructure construction projects contributes significantly to the sustainable reduction of solid wastes being landfilled. This research aims to evaluate the mechanistic performance of asphalt concrete with RAP and RCA modified with natural hemp fiber (HF) reinforcement (HF-RAP-RCA-AC). The effect of influence factors, such as RAP/RCA ratio, HF length, and HF content, on the static and dynamic-mechanistic performance was evaluated. The static performance of HF-RAP-RCA-AC was assessed through the Marshall stability (MS), strength index (SI), and indirect tensile strength (ITS), while the dynamic performance was evaluated through the indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), and rutting resistance tests. The HF-RAP-RCA-AC sample was found to have comparable static properties (MS and SI) to conventional asphalt concrete. The dynamic-mechanistic performance of HF-RAP-RCA-AC was however found to be significantly lower and hence HF-RAP-RCA-AC was found to be suitable for low-traffic roads. The improved ITS due to the addition of RCA and HF was found to influence the IT Mr improvement in the linear relationship. The improved resilient properties contribute to the ITFL and rutting resistance improvement. The optimum mix was found to be at 0.05%HF content, for all HF lengths and RAP/RCA ratios. The potential of HF reinforcement on the material properties was positively impacted by increasing the RCA content. The proposed distress model based on the critical analysis of the cyclic test data of HF-RAP-RCA-AC was developed and was found to have the same logarithm relationship. The outcome of this research will encourage the application of HF-RAP-RCA-AC as a sustainable pavement material for low-volume roads. [ABSTRACT FROM AUTHOR]

Asphalt mixture recycled technology (Al-Saffar et al. 2021) is an efficient method for achieving asphalt pavement sustainability. The optimum asphalt content of recycled asphalt mixture is first determined by the Marshall test in this paper. Second, Materials Studio software was used to simulate the interface effect between three different asphalts and aggregate, and the adhesion between asphalt and aggregate was characterised based on the interface energy. The mesoscopic structural characteristics of three asphalt mixtures were then analysed using digital image processing technology. Finally, through three macro experiments, the influence of old asphalt on the mechanical properties of recycled asphalt mixture was studied from a macro perspective. At the microscopic level, the results show that the presence of the old asphalt reduces the adhesion between the asphalt and the aggregate. At the mesoscopic level, the presence of old asphalt reduces the porosity of the asphalt mixture. At the macroscopic level, the addition of old asphalt improves the high temperature and water stability of recycled asphalt mixture while decreasing the low temperature crack resistance. The microscopic and mechanical properties of old asphalt on recycled asphalt mixture are explained on three levels, and new ideas for research on recycled asphalt mixtures are provided. [ABSTRACT FROM AUTHOR]

Reduce, reuse and recycle are treated as the thumb rule for achieving sustainability, and this formula rightly applies to construction materials as they are depleting at an incredible pace. Reclaimed asphalt pavement (RAP) is a sustainable alternative for construction aggregates. Several researchers have identified RAP as inferior material over natural coarse aggregates and proposed incorporating materials like superplasticizers, admixtures, fibers, and pozzolanic materials to compensate for the decrease in mechanical properties. Thus, the present study aims to evaluate the mechanical and durability characteristics of RAP-based roller-compacted concrete with red mud as part addition to cement. The present study considers a constant replacement percentage of 50% by weight of natural aggregates with RAP to evaluate mechanical and durability properties. Upon comparing the fresh properties of RAP-based roller-compacted concrete with red mud over roller-compacted concrete with only natural aggregates, a 3–15% increase in optimum moisture content is observed. Further, the mechanical properties like compressive, flexural, and tensile strengths, which showed a downtrend due to RAP inclusion, have significantly improved by incorporating red mud. However, a 15% red mud by cement weight is observed to be an optimum dosage based on the mechanical properties. Red mud-inclusive mixes outperformed RAP and control mixes in terms of durability characteristics such as water absorption, abrasion loss, and resistance to the aggressive environment. Further, incorporating 15% red mud in RAP-based roller-compacted concrete liberates a lower calcium silica ratio, which ascertains the dense microstructure formation. [ABSTRACT FROM AUTHOR]

The conventional design approaches for reclaimed asphalt pavement (RAP) mix follow blending rules to select the grade of the virgin binder for hot recycled bituminous mixtures. The interactions of RAP binder with the virgin binder are highly complex in the presence of the rejuvenator. Identifying the optimal proportion of RAP binder, virgin binder, and rejuvenator is often a trial-and-error procedure, involving considerable experimental data collection. The current research study proposes the statistical-based design of experiments (DoE) framework to design ternary RAP binder blend, develop response surface prediction models, and optimize the proportions to meet targeted binder properties of viscosity grade (VG30) binder. A desirability-based multiple response optimization is carried out, and the optimal blend proportions with target binder properties are arrived at with different desirability levels. A total of 13 RAP binder blends are formulated using the I-Optimal algorithm in the current study. Experimental data such as softening point, high-temperature performance grade (PG), and linear viscoelastic parameters in the temperature range of 46°C to 70°C and frequency range of 0.1 to 50 Hz are collected. The binder blends are evaluated using master curve parameters and relaxation spectrum. The response surface models are developed for two measured parameters (high-temperature PG and softening point), three computed master curve parameters, and four relaxation spectrum parameters. These models capture the possible individual component effects and combined component effects on the final RAP binder blend through linear and nonlinear terms. A desirability-based simplex optimization is adopted to identify combinations of constituents at various levels of desirability that comprises only direct measurements, direct measurements and master curve parameters, and direct measurements, master curve parameters, and relaxation spectrum. Using this proposed approach, a wide range of solution zones are identified with various levels of desirability. Reclaimed asphalt pavement (RAP) consisting of aged bitumen coated on mineral aggregates is used for recycling in pavement construction. Many challenges exist related to the optimal use of such material. The aged binder may need to have the required properties suitable for recycling. Generally, rejuvenators are added to the RAP to enhance the properties of aged binder. However, how much rejuvenator should be added is unclear. Aged bitumen from different sources of RAP can have different degrees of aging. In addition, it may not be easy to estimate the extent of blending of the RAP with the virgin materials (aggregates and bitumen), as it is linked to the characteristics of aged binder and the choice of fresh bitumen and rejuvenator. Also, the aged bitumen, when mixed with a rejuvenator and virgin bitumen, may not necessarily result in a final mix with bitumen that meets the requirements. As can be seen, the choices are entirely diverse and varied. This research attempts to solve such issues using a statistics-based tool called design of experiments (DoE). Using such a tool, this study demonstrates how to optimally choose the proportions of virgin bitumen, RAP bitumen, and rejuvenator. This work presents a methodology that can be implemented efficiently using commercial software by any asphalt mix designer. [ABSTRACT FROM AUTHOR]

Patching is a common pavement treatment, and it is implemented using hot and cold process patching. Hot process patching is not an efficient implementation method because keeping asphalt temperature in long hauls is difficult, on-site mixing equipment is required, and transport costs are generally high. Moreover, hot process patching requires a significant amount of energy, so it is not an eco-friendly process. Although cold process patching significantly reduces the energy consumption of patching, its implementation reduces the patching quality. To this end, this study aimed to propose a new cold process patching using induction heating. Furthermore, this study attempted to apply waste materials in the proposed mixtures to preserve the environment. Accordingly, high percentages of reclaimed asphalt pavement (RAP) were used in the proposed mixture. Since induction heating was applied in the introduced patching method, two waste materials, including steel slag and electronic waste, were utilized in the mixtures to enhance the sensitivity to electromagnetic radiation. Moreover, different experimental tests were conducted to evaluate the mixtures' mechanical properties. Ultimately, gray relational analysis was performed to assess the proposed mixtures' sustainability. The results indicated that using steel slag and electronic waste as conductive materials could considerably reduce the heating time to raise the fabricated mixtures' temperature. Moreover, replacing the Neat mixture with the proposed asphalt mixtures containing the waste materials significantly reduced the unit price, greenhouse gas emission, energy consumption, and raw material utilization. [ABSTRACT FROM AUTHOR]

The maximum permissible content of reclaimed asphalt pavement (RAP) is restricted due to its negative effect on the stability of hot mix asphalt with RAP (HMA-RAP) performance. To address this problem, characteristics of materials, including aggregate gradation, aged asphalt content, and aged asphalt properties, were quantified by testing RAP obtained from different sources. Additionally, the changing law and variability of the indexes are also analyzed. In accordance with the quality requirements of hot mixture asphalt stipulated by the Chinese standard, a control model of the maximum RAP content embraced in recycled asphalt mixture for hot central plant recycling is established. Furthermore, the distribution characteristic of asphalt content with respect to particle size is analyzed. Eventually, a fluctuation range model of blended asphalt penetration is established. The results indicate that (1) the variabilities of aggregate gradation, asphalt content, and aged asphalt properties of RAP are nonnegligible; (2) a control model regarding maximum permissible RAP content in HMA-RAP is proposed based on aggregate gradation and asphalt content; (3) the asphalt content and particle size of RAP are exponentially distributed, and the particle size elevates with the decrease of asphalt content; and (4) the fluctuation range of blended asphalt penetration is related to the asphalt content and penetration of aged asphalt, and the fluctuation range extends with the increasing of RAP content. This paper suggests that, to characterize the variability of RAP with its aggregate gradation and asphalt content, for RAP without pretreatment, the maximum permissible RAP content in HMA-RAP is recommended to be controlled under 30%. [ABSTRACT FROM AUTHOR]

Cement-emulsified asphalt (CEA) has been widely used in slab ballastless track and asphalt pavement cold recycling projects because of its high stiffness and toughness. In CEA material, emulsifiers and asphalt affect the cement's hydration process and microstructure. Thus, to further investigate the effects of anionic emulsifiers (AEs) and anionic emulsified asphalt (AEA) with different demulsification rates on the hydration process and microstructure of cement, two types of AE (rapid-setting and slow-setting) and their corresponding AEA were used to prepare modified cement pastes. First, it was confirmed that the AEs and AEA delayed cement hydration by measuring the setting time, X-ray diffraction (XRD) patterns, and electrical resistivity of the cement paste. Then, the microstructure of the cement paste was determined with mercury intrusion porosimetry (MIP) and a scanning electron microscope (SEM), and it was found that AEs and AEA have varying degrees of inhibitory effects on the formation of the cement paste microstructure. Finally, based on the energy dispersive spectrometer (EDS) element content of the cement paste and Fourier transform infrared spectroscopy (FTIR) on the two AEs, the inhibition mechanism of AE and AEA with different demulsifier rates on the cement hydration process was analyzed. The experimental results showed that both AEs and AEA delayed the hydration process of cement to varying degrees and altered the microstructure of cement, and slow setting anionic emulsified asphalt (SAEA) had the greatest impact on the hydration process and microstructure of cement. Compared to pure cement paste, the initial setting time of cement paste mixed with SAEA was delayed by 73.9%, and the final setting time was delayed by 66.7%. After adding SAEA, the most probable aperture of the cement paste increased from 62.50 nm to 71.19 nm after one day of hydration. Due to the fact that there were more carboxyl groups with negative charges, more -COO− was adsorbed onto the surface of cement particles in the slow-cracking anionic emulsifier (SAE); compared with the rapid-setting anionic emulsifier (RAE) and the rapid-setting anionic emulsified asphalt (RAEA), the SAE and the SAEA had a stronger delaying effect on the hydration reaction of cement. [ABSTRACT FROM AUTHOR]

The escalating quantities of waste are coming from old bituminous road pavements in Thailand has led to significant environmental and economic challenges. This research explores an innovative solution by investigating the feasibility of using Reclaimed Asphalt Pavement (RAP) as a substitute for natural coarse aggregate in roller compacted concrete (RCC). This study explores optimal proportions between cement to RAP-specifically at ratios of 1:6, 1:8, and 1:10-to achieve maximum dry density. The research includes essential tests, such as dry density and maximum compressive strength assessments, to determine the suitability of the material for compacted concrete production. Intriguingly, the research reveals that the 1:6 ratio not only has the highest dry density and maximum compressive strength but also may minimize environmental impact. These findings align with the ACI 325.10R-95 standard (1995), presenting a promising alternative for engineering applications and contributing to the responsible use of reclaimed materials. [ABSTRACT FROM AUTHOR]

The balanced mix design (BMD) constitutes a significant step forward in the pursuit of better-performing asphalt mixtures. This approach/framework offers increased innovative opportunities for the proper design and production of engineered asphalt mixtures without the need to strictly adhere to traditional volumetric requirements. The primary objective of this paper is to conduct a comprehensive investigation of the permanent deformation (rutting) behavior of surface mixtures (SMs) with conventional and high reclaimed asphalt pavement (HRAP) contents through full-scale accelerated testing under incremental loading conditions while accounting for the environmental aging effect. HRAP SMs were designed in this study, marking the initial application of Virginia Department of Transportation (VDOT) BMD special provisions, with attempts to incorporate 45% and even 60% RAP. Results showed that all BMD HRAP mixtures exhibited higher rut depths compared to the control mixture, which can be attributed to the inclusion of high binder contents aimed at enhancing cracking resistance. The asphalt pavement analyzer (APA) rut test and the stress sweep rutting tests were performed on mixtures sampled during production. Correlation analysis revealed significant and strong positive correlations between accelerated pavement testing (APT) and the multilevel laboratory rutting performance tests considered in this study. Finally, while acknowledging the limitations and all the assumptions considered in this study, the correlation analysis recommended refining the VDOT BMD APA rut depth threshold by lowering the current limit of 8 mm to 7 mm to ensure good performing mixtures from a rutting point of view. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) has been widely utilized because it is an environmentally friendly and economical material. The performance of recycled asphalt mixtures will deteriorate gradually with the secondary aging process of asphalt, including the self-healing property. To further understand the self-healing characteristics of asphalt after secondary aging, taking 70# petroleum asphalt, SBS-modified asphalt, and extracted old asphalt mastics as objects, the fatigue self-healing test and fracture self-healing test were conducted to simulate the intermediate-and low-temperature healing behaviors of different asphalt mastics. The impact of healing time, healing temperature, and aging degree of mastics on the healing performance was systematically investigated. The results show that the original unaged asphalt mastics present excellent fatigue healing properties with an index of 0.796 and 0.888 for 70# petroleum and SBS-modified asphalt mastics, respectively. The secondary aging process causes significant impact on the healing properties, leading to a great drop in the corresponding index, which decreased to 47.5% and 72.5% of that of the unaged ones. The fracture healing ability of all mastics was much inferior to the fatigue healing. After secondary aging, the fracture healing index values of 70# petroleum asphalt, SBS-modified asphalt, and extracted old asphalt mastics were all as low as around 0.3, indicating similar performance can be found in the secondary aged SBS-modified asphalt mastics and 70# asphalt mastics. Overall, after secondary aging, the fatigue damage of SBS-modified asphalt mastics can be cured effectively by self-healing, but the fatigue and fracture self-healing properties of 70# asphalt mastics are difficult to recover. These results could provide an innovative view to understand the fatigue and fracture healing characteristics of recycled asphalt pavement after secondary aging. [ABSTRACT FROM AUTHOR]

During blending between the binders in hot mix recycling, two physical processes occur, namely blending due to diffusion and blending due to mechanical agitation. In the present study, an experimental approach is developed to observe these processes directly on the laboratory recycled asphalt mix samples. Atomic Force Microscopy (AFM) and Confocal Laser Scanning Microscopy (CLSM) are used as the probing tools. The binder concentration profile is estimated at different locations around the reclaimed asphalt pavement material (RAPM) aggregate. Diffusion is observed to be predominant in some of these locations, while, in some other locations, mechanical mixing is observed to be predominant. Assuming that pure Fickian diffusion is happening at those diffusion-spots, the coefficient of diffusion is estimated from the concentration profile at those locations. It is envisaged that the proposed approach would provide a microscopic perspective of the extent of blending during the recycling process. [ABSTRACT FROM AUTHOR]

This study evaluated the impact of using different contents and sources of Reclaimed Asphalt Pavement (RAP) on the bottom-up fatigue cracking of asphalt mixtures and the return on investment (ROI). Two RAP sources were used that primarily provided a significant difference in RAP binder Performance Grade (PG): Source A was a PG 76-22 while Source B was a PG 94-10. Bottom-up fatigue cracking was predicted using Level 1 of the AASHTOWare Pavement Mechanistic-Empirical Design (PMED) software. The ROI was then evaluated using FHWA RealCost. To increase the accuracies of the predictions, volumetric properties and blended binder properties were calculated based on the amount of RAP binder that actively blended with the virgin binder. The accuracies were also increased by determining the AASHTOWare PMED fatigue strength coefficients, $k_{\,f1}$ k f 1 , $k_{\,f2}$ k f 2 , and $k_{\,f3}$ k f 3 , using flexural bending beam fatigue tests rather than using the global defaults provided by this software. In conclusion, the ROI of the six RAP mixtures based on bottom-up fatigue cracking was found to be affected by both RAP content and RAP source, and because of the effect of RAP source, it could not be generalised that using either a higher or lower RAP content will always provide a higher ROI. [ABSTRACT FROM AUTHOR]

Surface hot-in place recycling of asphalt mixtures has been conducted on Finnish roads for several years. The procedure is performed either in full-lane('remix') or shorter widths ('rut-remix'). In a 2020-2021 project, different mixture types were subjected to both kinds of recycling; reference mixtures, and mixtures modified with aramid fibres, FEP elastomer pellets, polymer, Storelastic rubber additive, recycled asphalt shingles, steel slag, and soft bitumen. This paper (Part II) presents the results of an extensive laboratory test plan at the bitumen scale. Asphalt mixture cores were recovered from four roads, and the bitumen was extracted fortesting. Various tests were performed on the bitumens in original state (aged, before recycling) and after recycling (remix or rut-remix), including FT-IR, DSR, MSCR, as well as bitumen content, penetration, and softening point. The master curves were constructed for all bitumens. Gradations are also presented herein. The effect of remix/rut-remix is evaluated via changes in all measured properties (including Glover-Rowe) before and after recycling, over a wide range of temperatures. The results complement the mixture-scale data and provide a comprehensive database of bitumen performance for an extended group of materials. Data appendices are accessible from the link at the bottom of the page. [ABSTRACT FROM AUTHOR]

This laboratory study investigates the feasibility of using geopolymer-based stabilization of base soil and reclaimed asphalt pavements (RAP) to fully replace cement in road rehabilitation projects. Geopolymer is an environment-friendly material that is based on the alkaline activation of aluminosilicate precursors. The performance of Portland cement as a chemical stabilizer for the full depth reclamation (FDR) of asphalt pavements is well established. However, Portland cement manufacturing has a high carbon footprint and other significant environmental impacts. Furthermore, there is a shortage of cement available for FDR projects across many country regions. Simultaneously, there is a strong motivation to explore various industrial wastes such as ponded ash, slag, ground glass fibers, etc., as replacements for Portland cement in construction. Therefore, a geopolymer based on ground glass fibers (GGF), either separately or combined with ponded fly ash (PFA) or slag (S), was studied to replace cement in FDR. All mixtures were tested for unconfined compressive strength (UCS), flexural strength, and drying shrinkage, wetting/drying, freezing/thawing, and tube suction tests. The results showed promising performance of geopolymer-based stabilized mixtures as compared to control. However, some test methods related to FDR with cement need to be modified to suit the mixtures of FDR with geopolymer. [ABSTRACT FROM AUTHOR]

Despite its significant role in cold recycling mix design and construction process, the effect of reclaimed asphalt pavement aggregates' gradation and physical properties are relatively less understood. The ambiguities associated with the gradation effect led to challenges in determining the best practices in gradation control and stockpile management and blending in both cold-in-place and central plant recycling operations. Therefore, the main goal of this paper is to quantify the impact of gradation changes and proportioning of reclaimed asphalt pavement aggregates on the packing characteristics and performance of cold recycled mixtures. Binary blends consisting of fine and coarse reclaimed asphalt pavement stockpiles were combined to obtain fourteen gradations using a volumetric aggregate proportioning technique. The compatibility of five of the most prominent binary aggregate packing models was evaluated in cold recycling application. The modified Toufar model was able to accurately predict the blend of fine and coarse aggregates that offers the optimum packing prediction. Complex modulus tests showed linear viscoelastic characteristics of the cold recycled mixtures as well as the sensitivity to the packing states. In essence, this research shows the effectiveness of applying volumetric packing principles and aggregate proportioning techniques to achieve improvements in cold recycled mixtures' volumetric and mechanical performance. [ABSTRACT FROM AUTHOR]

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is a routine process. Recycled binder availability reflects the proportion of the total recycled binder in a given recycled asphalt material (RAM) that is available to blend with the virgin binder. Studies show that agglomerations of adhered RAM particles preclude complete availability. However, the Superpave volumetric mixture design methods adopted by the majority of state agencies assume complete availability. This study makes use of a sieve analysis method and tracer-based microscopy analysis to quantify recycled binder availability. Revisions to asphalt mix design procedures to account for partial availability are proposed, including consideration of the unavailable binder as part of the bulk aggregate volume and the use of the RAM gradation (i.e. black curve) rather than the recovered aggregate gradation (i.e. white curve) to design the mixture's aggregate structure. Three high RAM content 'control' mixtures that were originally designed under the assumption of complete recycled binder availability are redesigned according to the proposed approach. The redesigned mixtures had notably higher virgin binder content than the control mixtures. The redesigned mixtures also had significantly better cracking resistance than the control mixtures while still meeting permanent deformation requirements. [ABSTRACT FROM AUTHOR]

A pavement aging model (PAM) is established by calibrating and validating the NCHRP 09–54 kinetics model's predictions against field core measurements. Field cores, laboratory-mixed loose mixtures, and binders from a wide range of pavement sections are used, including both conventional hot mix asphalt (HMA) mixtures and modern materials (i.e. reclaimed asphalt pavement (RAP), warm mix asphalt (WMA), and polymer modified asphalt (PMA)). Field aging levels are measured at different depths from binder extracted and recovered from in-service field cores. The original component materials of these pavement sections are aged in the laboratory and used to calibrate the kinetics model. The measured field aging levels are compared against those predicted from the kinetics model to inform a depth and time dependent field calibration function for the PAM. The validation of PAM using an independent set of field sections shows that, within the limited data used in this study, the calibrated PAM may be able to predict the aging of the conventional HMA, RAP, WMA, and PMA mixtures. The PAM predictions are lastly found to outmatch the predictions by the Global Aging System (GAS) model. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the effect of moisture damage on the fatigue and cracking behaviors of warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP). To achieve this aim, different fatigue and cracking tests such as indirect tensile fatigue failure, four point beam fatigue, and semicircular bending tests have been conducted, and several parameters have been obtained. These parameters include tensile strength ratio (TSR) and fracture energy ratio (FER), indirect tensile fatigue ratio (IDTR), peak load ratio (PLR), J-integral ratio, and flexibility index (FI), and Nf and flexural stiffness ratios. The results showed that moisture-damaged RAP-WMA demonstrated slightly weaker fatigue and cracking resistance than other mixtures, which is not significant considering the environmental advantages of the mixture. Hence, RAP-WMA would be a proper and beneficial alternative as pavement material where there are significant problems in supplying natural aggregates, and issues like moisture damage and being environment friendly are big concerns. Also, it has been concluded that the fatigue test condition (stress and strain control modes) had a significant effect on the moisture damage investigation. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) mixtures reduces environmental burden by utilising existing pavement material. However, RAP percent is limited due to performance issues at higher RAP content due to improper blending. The degree of blending can be improved using rejuvenator. Waste cooking oil (WCO) is gaining attention as a potential rejuvenator in recycled mixtures. However, past studies have shown contradictory results on WCO influence in asphalt mixture and have not investigated the influence of WCO on blending. This study is devised with a methodological approach to investigate the influence of WCO on blending in asphalt mixtures. Four blending approaches were formulated with four RAP and WCO contents resulting in a total of 148 mixture combinations. The blending characteristics were evaluated by assessing the workability and moisture damage resistance. The optimum mixtures were determined by Grey relational analysis, which were further investigated. The results showed the WCO doses determined from blending equation resulted in the higher dose than optimum WCO. The mixtures with medium dose and dry mixing of WCO showed the highest resistance to moisture damage. Further, for utilising higher than 30% RAP, higher binder content is required as compared to conventional mixture to increase the functional binder in the mixture. [ABSTRACT FROM AUTHOR]

Aging of asphalt binder is a complex natural phenomenon with significant differences under the effect of different environmental factors. The accelerated aging method commonly used in the laboratory is difficult to reproduce the field aging of asphalt binder. The purpose of this study is to reveal the effect of environmental factors on the aging gradient of asphalt binder. For this reason, a layered dissolution-peeling method was developed to recycle asphalt binder films. The gradient behaviour of field-aged asphalt binder was analysed based on rheological parameters and chemical functional groups. The results showed that the layered dissolution-peeling method achieved separation of asphalt binder at 0.1 mm level. Ultraviolet light severely contributed to the distinct aging gradient of field-aged asphalt binder. The carbonyl index of field-aged asphalt binder at 0–0.32 mm was approximately 1.73 times higher than that at 0.32–0.64 mm, 1.90 times higher than that at 0.64–0.96 mm and 2.24 times higher than that at 0.96–1.28 mm. To significantly characterise the aging behaviour of asphalt binder, the film thickness in the accelerated aging simulation test should not be more than 1 mm. The findings of the study serve as a valuable reference for accurate prediction and targeted prevention for asphalt pavements. [ABSTRACT FROM AUTHOR]

Conventional rejuvenation methods recover the rheological properties of aged bitumen by adding rejuvenators to supplement the content of light fractions of bitumen. However, these methods cannot fully restore the microstructure and advantages of aged asphalt rubber (AR) binder due to the dissolution of rubber particles. Aiming at discovering a more suitable rejuvenation strategy for reclaimed asphalt rubber pavement (RARP), this study investigates the rejuvenation mechanisms of RARP through a series of chemical and rheological tests at the mortar level. A chemistry-based method was proposed to estimate the rubber dissolution in RARP mortar. AR mortars containing 40% of RARP mortar (RARP40%) were prepared. Three rejuvenation schemes were adopted for RARP40%, namely recovering the light fractions, supplementing the swelling rubber content, and both recovering and supplementing, respectively. The results indicate that adding rejuvenator only can effectively soften the aged RARP binder but it fails to slow down the rheological evolution of RARP40% mortar in the secondary aging. The incorporation of AR binder with extra rubber content notably improved the aging resistance but significantly compromised the workability of RARP40% mortar. The compound rejuvenation scheme was the optimum solution that balanced the rejuvenation effectiveness, aging resistance and workability. [ABSTRACT FROM AUTHOR]

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

Waste cooking oil (WCO) is being investigated as a rejuvenator to utilise higher amount of reclaimed asphalt pavement (RAP) in asphalt mixtures. Past studies have evaluated the potential of WCO as rejuvenator without considering the performance of the rejuvenated binder after the secondary aging (long-term aging). The studies did not reveal any optimum amount of WCO required for the appropriate rejuvenation for incorporation of particular amount of RAP binder or aged binder. In this study, the potential of WCO is evaluated as rejuvenator of the binders incorporating higher aged binder by considering the anti-aging effect of WCO on the performance of rejuvenated binder after secondary aging. The study proposes a concept to determine the optimum dose of WCO for binders with different percentage of aged binder based on Equi-viscous concept and rutting criteria for short-term aged binder.Optimum dosages for the rejuvenated binders with 45, 60 and 75% RAP binder were found to be 6.45, 7.07 and 7.59%, respectively. The rejuvenated binders with different RAP contents and optimum WCO dosage showed lower susceptibility against fatigue and rutting. Further, the study concludes that the WCO can perform dual function as rejuvenator and also as an anti-aging additive. [ABSTRACT FROM AUTHOR]

This study explores different methodologies to select proper doses of three palm-oil-based rejuvenators to restore the properties of the effective binder present in asphalt mixtures with high Reclaimed Asphalt Pavement (RAP) content. Two commercial vegetable-based rejuvenators were also used as reference for comparison. The dose selection methods are based on penetration and softening point in unaged, short- and long-term aged states, and High Temperature Superpave Performance Grade (PGH) verified with Fatigue Low-Temperature Superpave Performance Grade (PGFL). In addition, a novel approach based on the thermodynamic properties of the recycled binder blends (i.e. mix of virgin binder, RAP binder and rejuvenator) quantified through the Surface Free Energy (SFE) measurements was also explored. In all cases, the optimum dose selection was determined by the amount of rejuvenator required to provide equivalent or better properties than the virgin binder in its unaged and aged conditions. The results suggest that the PGH approach verified with PGFL is the most appropriate method to determine the optimum rejuvenator dose. This methodology was initially validated by means of rheological and chemical testing conducted on the recycled binder blends at the selected dose in different ageing states. [ABSTRACT FROM AUTHOR]

Surface hot-in place recycling of asphalt mixtures has been conducted on Finnish roads for several years. The procedure is performed either in full-lane ('remix') or shorter widths ('rut-remix'). In a 2020–2021 project, different mixture types were subjected to both kinds of recycling; reference mixtures, and mixtures modified with aramid fibres, FEP elastomer pellets, polymer, Storelastic rubber additive, recycled asphalt shingles, steel slag, and soft bitumen. This paper (Part I) presents the results of an extensive laboratory test plan at the mixture scale. Asphalt mixture cores were recovered from four roads. Various tests were performed on the mixtures in original state (aged, before recycling) and after recycling (remix or rut-remix), including strength (ITSR), stiffness, Prall abrasion, creep permanent deformation, as well as bulk, air voids, and thickness measurements. The effect of remix/rut-remix is assessed using scores calculated from mixture-scale test results. The results show that remix and rut-remix are highly heterogeneous processes, affecting every material differently and sometimes erratically. Adequate air void contents and evenness in compaction are critical for good performance. The results provide a reference performance database for an extended group of materials. Data appendices are accessible from the link at the bottom of the page. [ABSTRACT FROM AUTHOR]

This paper studies the potential effects of Reclaimed Asphalt Pavement (RAP) fine particles on bituminous mixtures by means of a laboratory investigation performed at the mastic scale. Bituminous mastics, characterised by a constant filler to bitumen volume ratio, were prepared by combining virgin filler and virgin bitumen with several dosages of RAP fine particles. The influence of RAP type was evaluated by employing two RAP products supplied by different sources. The rheological behaviour of the mastics was investigated by means of oscillatory tests carried out with a dynamic shear rheometer. The time-temperature superposition principle and the generalised self-consistent scheme (GSCS) micromechanical model were used to explore the role played by RAP at the mastic scale. Results indicate that the adopted experimental and modelling approach allows a proper assessment of the effects of RAP on the linear viscoelastic properties of mastics and of the degree of blending occurring between virgin and RAP binder. [ABSTRACT FROM AUTHOR]

Realizing the utilization of reclaimed asphalt binder (RAB) and rice husk (RH) to reduce environmental pollution and expand the reutilization technique of reclaimed asphalt pavement (RAP), co-pyrolysis of RAB with RH has great potential. In this study, the co-pyrolysis behaviors, gaseous products, and kinetics were evaluated using thermogravimetric analysis and Fourier transform infrared spectroscopy (TG-FTIR). The results showed that incorporating RH into RAB improved its pyrolysis characteristics. The interactions between RAB and RH showed initial inhibition followed by subsequent promotion. The primary gaseous products formed during co-pyrolysis were aliphatic hydrocarbons, water, and carbon dioxide, along with smaller amounts of aldehydes and alcohols originating from RH pyrolysis. All average activation energy values for the blends, determined through iso-conversional methods, decreased with RH addition. The combined kinetic analysis revealed two distinct mechanisms: (1) at the lower conversion range, the pyrolysis of the blend followed a random nucleation and three-dimensional growth mechanism, while (2) at the higher conversion range, the control mechanism transitioned into three-dimensional diffusion. [ABSTRACT FROM AUTHOR]