Search Results (280)

This study examines how reclaimed asphalt pavement (RAP) dosage, virgin-binder grade, and virgin-binder content govern the cracking response of Marshall-designed mixtures. The experimental matrix comprised four RAP levels (30%, 40%, 50%, and 60%), two modified virgin binders (PG 76-22 and PG 88-34) evaluated at their respective optimum asphalt contents (OACs), and two binder-rich PG 76-22 variants (OAC + 0.3 and OAC + 0.5 percentage points); virgin mixtures served as controls. Cracking behavior was characterized by low-temperature semi-circular bending (SCB), the Illinois Flexibility Index Test (I-FIT), and direct-tension cyclic fatigue (DTCF). Fracture and fatigue indicators were subsequently integrated into cracking balance design diagrams, and k-means clustering was used to derive provisional, dataset-specific performance boundaries for long-term oven-aged mixtures. The results show that the higher-performance binder improved long-term cracking resistance at moderate RAP contents. By contrast, mixtures with 50% or 60% RAP and PG 76-22 displayed a distinctly brittle response. Increasing the PG 76-22 content above OAC produced only limited gains. These findings demonstrate that binder quality, rather than a small increase in binder dosage, is the more effective lever for balancing fracture and fatigue resistance in mixtures with substantial RAP contents. Full article

Recycled micro-surfacing is a sustainable pavement maintenance technique, yet using fine Reclaimed Asphalt Pavement (RAP) is challenging due to aged asphalt and particle agglomeration. This study aimed to develop cold recycled micro-surfacing with waste edible oil (WEO) and Waterborne Epoxy Resin (WER)-modified emulsified asphalt and proposed a novel pre-regeneration method using ultrasonic–mechanical mixing for fine RAP with WEO before preparing mixtures. Molecular dynamics (MD) simulation and Dynamic Shear Rheometer (DSR) tests were conducted to assess rejuvenator diffusion and rheological recovery. In addition, mixtures with 0–25% WER were tested for wear, rutting, low-temperature splitting, and water resistance to optimize the WEO content, mixing time, and WER dosage. The results of MD simulation showed that WEO diffused faster than aged asphalt molecules and mutually interacted. DSR results indicated that 4% WEO (by mass of aged asphalt) gradually restored the complex modulus and phase angle to the levels of matrix asphalt. The recycled mixtures with 4 min ultrasonic–mechanical mixing had a minimum WTAT of 136.86 g/m², which was a 9.6% decrease compared to the mixture without ultrasonic–mechanical mixing. The 1 h WTAT, PVD, PLD, 6d WTAT, and tensile strength of recycled mixtures with 20% WER were improved by 72.6%, 68.9%, 68.8%, 75.0%, and 88.7% compared with those of the matrix asphalt mixtures. Although WER weakened the low-temperature performance of the mixtures, the tensile strain was smaller than the maximum specification requirement of 2500 με when the WER content was less than 20%. In summary, pre-regeneration with 0.4% WEO (by mass of mixtures) and 4 min ultrasonic–mechanical mixing effectively activated the fine RAP. Considering the balance of properties of fine RAP micro-surfacing mixtures, the optimum dosage of 20% WER was recommended to provide sustainable high-performance cold recycled micro-surfacing. Full article

The increasing demand for sustainable road infrastructure has encouraged the development of asphalt mixtures incorporating recycled materials and industrial by-products. This study developed and validated a highly circular AC14 asphalt surface mixture incorporating steel slag aggregates (SSA) and reclaimed asphalt pavement (RAP). The laboratory-designed mixture contained 63.8% SSA and 17.2% RAP, corresponding to 81.0% secondary materials, or 83.0% when recovered filler is included. Its volumetric and mechanical performance was compared with that of a conventional AC14 surface mixture with natural aggregates. The highly circular formulation was then produced in an asphalt plant and applied in a full-scale field trial. A life cycle assessment (LCA), following EN 15804:2012+A2:2019, and a production-stage cost analysis were conducted using plant-specific data. The highly circular mixture showed improved rutting resistance, higher stiffness modulus, very high resistance to water damage, and better fatigue indicators than the conventional reference mixture. The field trial supported its feasibility under real production and construction conditions. The LCA showed reductions in 12 of the 13 product-stage environmental impact indicators, including reductions of 18.1% in total global warming potential, 26.6% in abiotic depletion potential for fossil resources, 77.6% in abiotic depletion potential for minerals and metals, and 81.5% in water deprivation potential. The estimated production-stage unit price was 36.4% lower than that of the conventional mixture and 45.4% lower than the Portuguese market benchmark. These results demonstrate the technical, environmental, and economic potential of highly circular asphalt surface mixtures incorporating SSA and RAP. Full article

This study developed a conditioning framework for the sustainable use of waste-engine-oil-modified binders (WEOMBs) in 100% reclaimed asphalt pavement (RAP) mixtures. Binder with a penetration grade of 60–70 was modified by 5%, 8%, and 10% waste engine oil (WEO) by binder weight. The WEOMBs were subjected to physical, chemical, and compositional analyses. For 10% WEOMB, the results showed a reduction of the binder softening point by 18% and an increase in binder penetration of almost 8%, enhancing softening and the workability of the binder. Binder chemical and compositional analyses verified that WEO altered the binder’s colloidal structure by augmenting aliphatic fractions and molecular mobility, while diminishing resin content and promoting saturates plus aromatics content. At 160 °C for 45 min, the RAPs were conditioned with 1% WEOMB (containing different WEO percentages) by the total weight of the RAP mixture. Among all the conditioned mixtures, the 100% RAP modified with 1% WEOMB, containing 8% WEO, showed the best performance. Dynamic modulus and phase angle analyses demonstrated that RAP conditioning reduced excessive stiffness and produced a balanced viscoelastic response, enhancing the rutting resistance. The proposed conditioning framework demonstrated the feasibility of producing fully recycled mixtures with balanced mechanical performance and adequate cracking resistance. Full article

Warm mix asphalt (WMA) provides a sustainable way of lowering production temperatures, reducing energy use for sustainable pavement construction; however, moisture damage affects its durability. Reclaimed asphalt pavement (RAP) contains aged binder that is stiffer, harder, and more brittle than virgin binder, resulting in asphalt mixtures with higher stiffness/modulus. This review examines the effect of incorporating RAP to amend the moisture damage susceptibility of WMA. It surveys the various moisture-damage failures reported in the literature on WMA with RAP mixes, including adhesive and cohesive failures, as well as hydraulic scouring and aggregate fracture. The analysis further explains the influence of WMA technology, RAP content, rejuvenation, and interfacial chemistry on the moisture durability of WMA-RAP mixtures. The strengths and limitations of the conventional and emerging moisture damage evaluation tests, including AASHTO T 283 tensile strength ratio (TSR), boiling water test (BWT), surface free energy (SFE), and fracture-energy-based approaches, were compared. This mechanistic synthesis linking production-related moisture sources, RAP heterogeneity and practical mitigation strategies highlights why reliance on TSR alone can conceal moisture-cracking vulnerability. The synthesis clarifies how RAP changes the moisture damage susceptibility of WMA to retain the environmental, economic and social benefits and circularity without compromising durability. This review proposes a practical roadmap based on technology-specific screening, multi-metric performance evaluation, and construction quality control for more reliable WMA-RAP specifications. Full article

The reuse of reclaimed asphalt pavement (RAP) offers economic and environmental benefits in road construction. However, its inconsistent quality—stemming from material complexity and poor management—limits its efficient and high-value application. A key factor contributing to RAP variability is particle agglomeration, where aged asphalt mortar binds aggregate together, leading to inaccurate aggregate gradation measurements and unpredictable contributions of aged binder. These inconsistencies reduce the uniformity and mechanical performance of recycled asphalt mixes. This paper provides a critical review of refined RAP separation treatments recently developed as supplementary RAP processing techniques to reduce variability and enhance performance consistency. Among these methods, rotary centrifugal decomposition has emerged as a promising technique for disaggregating RAP agglomerates and recovering coarse aggregates with minimal residual aged asphalt. Large-scale applications have demonstrated its efficiency in producing well-graded RAP fractions, typically separating recycled coarse aggregates (5–20 mm) from bitumen-rich fine RAP (0–5 mm). Despite its potential to improve RAP recycling rates and high-RAP-content mix performance, challenges remain in preserving coarse aggregate integrity, controlling gradation refinement, and managing the bitumen-rich fine fractions. Therefore, further research is needed to optimize the separation process to minimize material degradation and excessive fine fractions and assess long-term practicality and cost effectiveness through life-cycle analysis. Full article

The use of reclaimed asphalt pavement (RAP) has been increasing due to its economic benefits and environmental sustainability. Adding RAP materials introduces age-hardened binder, which tends to increase the rutting resistance but decrease cracking resistance. This study aims to evaluate the effects of various RAP contents and binder additives on asphalt performance using the Hamburg wheel tracking test, the Semi-Circular Bending-Illinois Flexibility Index Test (SCB-IFIT) and the Indirect Tensile Asphalt Cracking Test (IDEAL-CT). Asphalt mixtures with RAP contents of 0%, 20%, 30%, 40%, and 50% were prepared using two different binder additives of Zero-M polymer cool mix asphalt additive (PCMA) and Anova vegetable oil-based rejuvenator. Based on the Hamburg test results, the rutting resistance significantly increased by adding 20% RAP but did not increase the rutting resistance any further when RAP increased from 20% to 50%. However, the increase in RAP content exhibited a negative impact on cracking resistance by lowering Flexibility Index (FI) based on the SCB-IF test by 50% or more and CT Index (CTindex) based on IDEAL-CT test by 60% or more. For each RAP content, asphalt mixtures incorporating two different additives were tested: (1) Zero-M additive at a dosage rate of 10% of the total binder with mixing/compaction temperature of 110 °C and (2) Anova additive at a dosage rate of 5% of the RAP binder with mixing/compaction temperature of 135 °C. Compared to the control specimens without additive, asphalt mixtures with Zero-M additive increased FI and CTindex by 50% except CTindex of 30% RAP mix. Zero-M additive increased the rut depth from 3 mm to 10 mm for 20% and 30% RAP mixes but, for 40% and 50% RAP contents, the rutting was less than 5 mm after 20,000 repetitions. Anova rejuvenator did not increase FI and CTindex of 30% and 50% RAP mixes but increased FI and CTindex by 50% for 40% RAP mix. Anova additive did not increase the rutting of the control mix. The SCB-IFIT test results exhibited an average coefficient of variation (COV) of 0.25 whereas the IDEAL-CT test results had a COV of 0.20. The IDEAL-CT test, with its simpler preparation process and more consistent results, is recommended as the preferred test procedure over the SCB-IFIT test. Full article

High reclaimed asphalt pavement (RAP) mixtures can improve pavement sustainability by reducing virgin binder and aggregate demand, but high RAP contents may increase mixture stiffness and reduce cracking tolerance. This study evaluates whether commercially available para-aramid fibers can improve the intermediate-temperature cracking resistance of high-RAP hot-mix asphalt using the IDEAL-CT test. Two para-aramid fiber products, a wax-coated fiber and an emulsion-treated fiber, were evaluated at dosages of 0.05%, 0.10%, and 0.15% by total mixture weight in asphalt mixtures containing 15%, 25%, and 40% RAP. The results showed that fiber effectiveness depended strongly on RAP content, fiber treatment, and dosage. The 25% RAP mixture had the lowest control CTIndex and showed the greatest improvement from fiber addition. In this group, 0.10% wax-coated fiber increased CTIndex by 170%, while 0.15% emulsion-treated fiber increased CTIndex by 263%. For the 15% RAP mixture, 0.05% emulsion-treated fiber and 0.10% wax-coated fiber produced statistically significant improvements. For the 40% RAP mixture, 0.10% emulsion-treated fiber produced the highest mean CTIndex among all mixtures tested, but the improvement was not statistically significant because of high specimen variability. Overall, the findings indicate that para-aramid fibers can improve laboratory cracking resistance in RAP mixtures, but the optimum dosage is mixture-specific and should not be applied uniformly across RAP contents. Because this study was limited to Ideal-CT, additional rutting, fatigue, aging, workability analysis and field validation are recommended before broad implementation. Full article

The development of recycled asphalt mixtures combining reduced production temperatures with adequate mechanical performance remains challenging in circular pavement engineering. This study assessed the performance-based redesign of a half-warm mix asphalt (HWMA) produced at approximately 90 °C with a very high reclaimed asphalt pavement (RAP) content and foamed bitumen, using previously validated cold recycled mixture (CRM) and hot recycled mix asphalt (HRMA) formulations as contextual benchmarks. An initial CRM-derived HWMA was evaluated to assess whether cold-recycling design logic could be transferred to half-warm production without added water or cement. Although the mixture showed satisfactory volumetric and moisture-related responses, wheel tracking identified rutting as the governing limitation. The mixture was redesigned by incorporating coarse steel slag aggregate (SSA) to correct the aggregate size distribution, reducing filler content and adjusting the added foamed bitumen while maintaining RAP and SSA at 98% of the aggregate skeleton. The combined redesign reduced the wheel-tracking slope in air from 1.25 to 0.32 mm/10³ cycles and the proportional rut depth in air from 28.1% to 10.4%. Nevertheless, the redesigned HWMA remained less rut-resistant than both benchmarks, confirming the need for further optimisation. It achieved stiffness close to the HRMA benchmark and a fatigue response compatible with base-layer application, although moisture durability requires further validation. Overall, the study demonstrates the feasibility of a sequential performance-based redesign approach for high-RAP HWMA while highlighting the need for systematic optimisation and field validation before broader implementation. Full article

The growing use of reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA) is an important practice to achieve more sustainable pavements, as it reduces the consumption and environmental impact of virgin materials. However, aging induces binder stiffening that requires effective rejuvenation to restore overall performance. This study provides a comprehensive comparative analysis of ten chemically different waste oils—waste engine oil (WEO), waste cooking oil (WCO), yellow grease (YG), waste hydraulic oil (WHO) waste electric transformer oil (WETO), slop oil (SO), sludge-derived bio-oil (SDBO), tire pyrolysis oil (TPO), plastic pyrolysis oil (PPO), and algal residue oil (ARO)—as recycled HMA mixture rejuvenators, linking oil composition to binder regeneration and mixture performance. Binder properties were determined by rotational viscosity (RV), dynamic shear rheometer (DSR) and bending beam rheometer (BBR), whereas mixture performance was assessed in terms of Superpave mechanical properties, Hamburg wheel-tracking test (HWTT) for rutting resistance and mixture BBR for low-temperature cracking resistance. Performance grade (PG) evaluations showed that WETO and WEO restored the 50% and 75% RAP binders, respectively, to a grade close to PG 64-16 at the lowest dosages. The Superpave volumetric properties of all restored mixtures were similar to those of the control mixture, denoting corrected mixture balance and compaction level. HWTT results indicated that WETO-recycled mixtures revealed the lowest rut depth at 50% RAP, while WEO-recycled mixtures exhibited the lowest rut depth at 75% RAP after 20000 passes. Additional evidence supporting these results can be found in BBR mixture data, which demonstrated that WETO at 50% RAP and WEO/WETO at 75% RAP showed the most reduction in creep stiffness and improvement in creep rate. The correlation, regression, and PI analyses were in good agreement with the experimental results, where WETO and WEO exhibited the best overall performance at 50% and 75% RAP, respectively. In summary, these results indicate that the performance of waste oil rejuvenator in recycled HMA mixtures is highly dependent on RAP content and point to WETO and WEO as feasible, environmentally friendly options for high-RAP recycled HMA. Full article

Road construction contributes to embodied carbon in infrastructure, with asphalt-bound layers often dominating construction-stage greenhouse gas emissions in flexible pavements. Reclaimed asphalt pavement (RAP) and high-modulus asphalt concrete can reduce virgin material demand and improve structural efficiency, but their sustainability benefit depends on maintaining equivalent pavement performance. This study develops a climate-informed, mechanistic, environmental, and economic Pareto optimization framework for RAP-modified high-performance asphalt concrete (RAP-HPAC) pavement sections in Alberta. The framework couples fitted dynamic modulus master curves, monthly pavement temperature inputs, ALVA layered elastic analysis, Asphalt Institute fatigue and rutting criteria, A1–A5 global warming potential (GWP), and Alberta 2026 installed unit-price cost data. The RAP-HPAC mixture contains 50% RAP and was designed through a balanced mix design to target approximately 80% effective RAP binder activation. Three traffic classes were evaluated: 731, 1300, and 5426 ESAL/day/direction, each with 2% annual compound growth over a 20-year design period. Relative to independently optimized conventional HMA controls, Pareto-selected RAP-HPAC sections reduced P50 construction-stage GWP by approximately 19–30% and first cost by approximately 6–11% at a conservative 0.90× RAP-HPAC cost multiplier. The results show that RAP-HPAC is most beneficial when used as a structural-bound base that replaces conventional asphalt-bound capacity while preserving sufficient granular support. The framework provides a reproducible design-stage approach for comparing recycled high-modulus asphalt mixtures using performance, carbon, and cost criteria simultaneously. Full article

The need for potentially more sustainable road rehabilitation solutions has driven the use of reclaimed asphalt pavement (RAP) in bituminous mixtures. However, high-RAP content remains a technical challenge due to binder ageing, which increases mixture stiffness and adversely affects its mechanical performance. The aim of this research is to evaluate three strategies for correcting aged binder in asphalt concrete (AC) 16 surf S mixtures containing 50% RAP: rejuvenator, regenerator, and softer virgin bitumen. To this end, four asphalt mixtures were evaluated through tests on air void content, water sensitivity, resistance to permanent deformation, and stiffness modulus, in accordance with European standards. The results show that the reference mixture without binder correction exhibits excessive stiffness, whereas the mixture incorporating a rejuvenator showed the most favorable combination of the mechanical indicators evaluated, combining a significant reduction in stiffness modulus with high water resistance and adequate rutting resistance. The mixture with regenerator showed an intermediate response, while the exclusive use of a softer bitumen did not achieve satisfactory overall performance. The results confirm that the use of high-RAP contents in AC 16 surf S mixtures can be feasible, provided that an appropriate strategy for rheological correction of the aged binder is applied. Full article

This study investigates asphalt mixture workability using a high-capacity torque-based device under semi-industrial laboratory conditions. Unlike conventional laboratory-scale mixers, the proposed system accommodates batch sizes up to 15 kg, enabling more realistic simulation of plant and field mixing conditions. Torque response was monitored during the mixing of conventional, warm-mix, and RAP-containing asphalt mixtures. Predictive models were developed using stepwise regression to relate torque to mixture parameters, including temperature, RAP content, and binder type. Results indicate that RAP significantly increases mixing torque, while elevated temperatures reduce resistance to mixing. Although the developed models demonstrated moderate to good explanatory power (R² = 0.63–0.77), they provide useful comparative insights into asphalt mixture workability rather than absolute predictions. The proposed torque-based methodology offers a practical framework for workability assessment and quality control of asphalt mixtures beyond traditional laboratory scales. Full article

Foamed asphalt cold recycling technology is one of the key engineering approaches to address the accumulation of large quantities of reclaimed asphalt pavement (RAP) in road maintenance and rehabilitation. However, a systematic design methodology that simultaneously accounts for long-term fatigue resistance and toughness has not yet reached a unified consensus or widespread application. Existing studies have investigated the effects of fine aggregate gradation or cement content on individual performance aspects of mixtures, but studies incorporating both factors into a unified experimental framework for parallel comparison of multiple performance indicators remain limited. To this end, this study designed three mineral aggregate gradations with significantly different fine aggregate contents and systematically evaluated the effects of gradation composition, foamed asphalt content, and cement dosage on the mechanical properties, moisture stability, high-temperature stability, and fatigue performance of the mixtures. Indirect tensile fatigue tests under a stress-controlled mode were conducted to determine the fatigue life of different gradations at four stress ratio levels. The results indicate that sufficient fine aggregate content, particularly particles smaller than 0.075 mm, is a key factor in enhancing mixture compactness, indirect tensile strength, and resistance to moisture damage. The effect of cement on fatigue performance exhibits stress-level dependency: at low stress ratios, the addition of cement improves fatigue life, whereas at high stress ratios, the increased brittleness of the material reduces fatigue resistance, which is consistent with findings reported in previous studies. Furthermore, this study provides comparative experimental data for different fine aggregate gradations. The optimal gradation scheme demonstrated superior overall performance across all evaluated indicators, verifying the feasibility of achieving a balance between strength and toughness through gradation optimization. Compared with conventional design methods guided by a single strength index, this study offers a more comprehensive basis for mix design optimization of foamed asphalt cold recycled mixtures and provides engineering references for their application in long-life pavement maintenance. Full article

The growing demand for sustainable and economically efficient road maintenance solutions has driven the development of materials that reduce the use of natural aggregates and promote waste valorization. In this context, this study evaluates the use of reclaimed asphalt pavement (RAP) and greywacke aggregates derived from Panasqueira mining by-products as partial or total substitutes for granite aggregates in cold asphalt mixtures intended for rapid pothole repair. Reference mixtures and recycled mixtures were produced with controlled proportions of RAP and greywacke, using cationic bituminous emulsion and hydrated lime, as well as an additional mixture composed only of RAP with a fluxing cold binder. Three commercial mixtures, identified as CCM1, CCM2, and CCM3, were also evaluated. Performance was analyzed through Cantabro particle loss, Marshall stability and flow, indirect tensile stiffness modulus, and water sensitivity (ITSR). The results show that greywacke provides a robust granular skeleton, while RAP content and binder type influence stiffness, cohesion, and moisture resistance. Overall, the combination of RAP and greywacke proved to be technically viable and, in several cases, superior to the commercial mixtures studied. Full article