Search Results (517)

Road pavement construction generates a significant initial carbon footprint, mainly related to material production, transport and construction processes. This study comparatively assesses the “cradle-to-site” carbon footprint of selected road pavement structures, with the aim of supporting low-carbon pavement design choices. The analysis was carried out using the Life Cycle Assessment (LCA) methodology, modelled with the open-source software OpenLCA^®, adopting a “cradle-to-site” approach limited to the production and construction phases. Several scenarios were examined by varying the percentages of recycled material content (RAP—Reclaimed Asphalt Pavement) used in asphalt mixtures, the functional road category and the pavement structural type. The results show that the reference flexible pavements produce approximately 70 kg CO₂ eq/m², with asphalt mixtures accounting for the largest share. The use of RAP enables emission reductions of up to 14%, although marginal benefits decrease as the recycled material increases. Impacts also vary according to the functional road category, ranging from approximately 50 to more than 90 kg CO₂ eq/m² when moving from local roads to motorways. Within the adopted cradle-to-site boundary, the LCA model supports the early-stage comparison of alternative pavement designs. Full article

Polyurethane (PU) is widely used in construction, transportation, automotive products, decorative materials, and related industries because its molecular structure can be tailored to diverse service requirements. This versatility has stimulated growing interest in polyurethane-modified asphalt for pavement engineering. This review examines the chemical structure, reaction mechanisms, and principal synthesis routes of polyurethane-modified asphalt and discusses polyurethane-modified emulsified asphalt, polyurethane composite-modified asphalt, and polyurethane-modified asphalt mixtures. Engineering applications in permeable pavements, bridge and tunnel surfacing, as well as crack and pothole repair are also considered. The review further addresses green in situ polymerization, high-content polyurethane systems, waterborne polyurethane, interfacial adhesion, bio-based formulations, recycled asphalt mixtures, and life-cycle performance. The available evidence indicates that polyurethane can improve high-temperature stability, durability, fatigue resistance, mechanical strength, adhesion, and aging resistance. In suitable formulations, it can also reduce production temperatures and construction-related emissions. Economic feasibility, unresolved technical issues, and future research priorities are discussed at the end of the review. Full article

Emulsion-based cold recycling can reduce the demand for virgin aggregate and high-temperature asphalt production, but mixtures with high reclaimed asphalt pavement (RAP) contents often have limited early strength and moisture resistance. This study evaluated a dense-graded cold-mix system containing 0%, 60%, and 70% RAP, combined with a 2 × 3 additive matrix comprising cement (0.5% and 1.0%) and Class C fly ash (0.5%, 1.0%, and 1.5%). The 70% RAP blend fell outside the adopted dense-graded envelope, whereas the 60% blend satisfied that envelope and was therefore selected, not claimed as a universal optimum for the additive stage. Hot-mix asphalt was included only as a benchmark. Marshall stability, indirect tensile strength, Marshall quotient, tensile strength ratio, retained Marshall stability, and retained Marshall quotient were measured under the reported laboratory curing and conditioning procedures. Among the tested cold mixtures, the 60% RAP formulation containing 1% cement and 1% fly ash produced the highest measured stability (13.1 kN), dry indirect tensile strength (1.11 MPa), and Marshall quotient (6.89), with retained-property indices of approximately 87%. These short-term results indicate that gradation control and low-dose cementitious additions can improve strength development and moisture retention in the studied emulsion–RAP system. The contribution of the work is an integrated, formulation-level comparison of RAP screening and a cement–fly ash dosage matrix; the findings remain specific to the materials, gradation envelope, curing regime, and screening tests used. Full article

Asphalt pavements suffer from progressive deterioration during service life due to aging, while conventional polymer modifiers raise environmental concerns regarding recyclability and volatile organic compound emissions. Functionalized-biochar derived from renewable biomass offers a sustainable alternative through its tunable surface chemistry and porous structure. This study develops and evaluates a nitrogen-rich, surface-functionalized biochar as a multifunctional asphalt binder modifier and elucidates the synergistic roles of inherent nitrogen and post-synthetic functionalization in governing binder performance. To this end, soybean powder was pyrolyzed to prepare the biochar precursor, which was subsequently characterized to determine its suitable pyrolysis temperature and surface properties. These analyses identified 300 °C as the preferable pyrolysis temperature within the tested range of 200–500 °C, maximizing biochar yield and achieving favorable surface physicochemical properties including the iodine adsorption value, oil absorption value, surface functional groups and pore morphology. To improve surface functionality, the biochar underwent a two-step modification: nitric acid oxidation followed by hydroxymethylation, hereinafter referred to as functionalized-biochar. The influence of functionalized-biochar content on asphalt binder performance was evaluated across dosages of 10–20 wt%, and 15 wt% was identified as the recommended content. Asphalt binder modified with 15 wt% functionalized-biochar exhibited improved high-temperature performance, as evidenced by enhanced rutting resistance factor G*/sin δ values obtained from dynamic shear rheometer testing. Aging resistance also improved, reflected in a lower complex modulus aging index and a higher phase angle aging index. At 15 wt% dosage, the softening point increased by 6 °C, and ductility rose by 10.6 cm relative to the base asphalt (1.9 cm), corresponding to a 557.9% improvement. Penetration declined by 17%, while the complex modulus aging index decreased from 3.44 to 1.68. Notably, the experimental program in this study was limited to binder-scale characterization. Full article

Cold recycled mixtures with bitumen emulsion (CRME) serving in seasonally frozen regions are susceptible to mechanical deterioration under repeated freeze-thaw (F-T) cycles, which is primarily manifested as interfacial damage and crack propagation. However, the micro-mechanical processes associated with the transmission and dissipation of frost-heaving stresses induced by water-ice phase transition within the interfacial transition zone (ITZ) between reclaimed asphalt pavement (RAP) and asphalt mortar remain to be further characterized. In this study, a numerical simulation approach coupling frost heave effects with the phase transition of water-ice particles was developed based on X-ray computed tomography (CT) and the discrete element method (DEM), and the micro-mechanical parameters of the RAP-asphalt mortar ITZ were determined through laboratory experiments. Combined with acoustic emission (AE) monitoring, the damage evolution characteristics of cold recycled mixtures and the associated interfacial damage mechanisms under freeze-thaw action were systematically investigated. The results indicate that the optimal micro-parameters of the RAP-asphalt mortar ITZ can be taken as approximately 85% of those of virgin asphalt mortar. After 20 freeze-thaw cycles, the number of shear cracks and tensile cracks in ITZ on RAP surface reached 493 and 92, respectively, which were much higher than 11 and five on the surface of new aggregate. ITZ was the main control weak area of freeze-thaw damage. Compared with the unfrozen specimens, the minimum effective contact number of mortar decreased by 1.63%, 4.52% and 8.52% respectively after 5, 10 and 20 freeze-thaw cycles, and the total effective contact number decreased from 75,842 to 69,383. Freeze-thaw cycles significantly reduce the strain energy storage capacity of CRME: the maximum energy storage capacity of the adhesive spring decreased from 2.15 J in the non-freeze-thaw state to 1.28 J in 10 cycles (a decrease of 40.47%) and 1.16 J in 20 cycles (a decrease of 46.05%), and the damage mode changed from brittle fracture to interface-controlled energy dissipation. The proposed water-ice phase transition-based DEM framework provides a reliable numerical tool for investigating freeze-thaw damage mechanisms and supporting durability-oriented design of cold recycled pavement materials. Full article

The increasing generation of construction and demolition waste, along with the depletion of natural aggregates, has driven growing interest in recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) as sustainable alternatives in concrete production. However, a direct and systematic comparison between the two materials remains limited. This review addresses this gap by applying PRISMA guidelines to analyze 82 peer-reviewed studies published between 2010 and 2026. Both materials are evaluated across three key domains: physical properties, mechanical performance, and microstructural characteristics. The findings indicate that RCA can reduce compressive strength by up to 26%, mainly due to the presence of porous adhered mortar and a complex interfacial transition zone (ITZ). In contrast, RAP weakens bonding with cement paste because of its hydrophobic bituminous coating, leading to adhesive failure at the mortar asphalt interface. Despite these limitations, RCA and RAP exhibit distinct behaviors in terms of shear capacity, ductility, energy absorption, and durability. Enhancement techniques such as surface treatment, carbonation, supplementary cementitious materials, and fiber reinforcement show potential in improving performance. Additionally, life cycle and economic analyses reveal that RAP can reduce total costs and carbon emissions when efficiently processed. This study provides a unified comparative framework to support sustainable material selection and design optimization. Full article

Growing demand for pavement maintenance promotes reclaimed asphalt pavement (RAP) recycling, yet multi-scale comparative research on rejuvenators remains limited. This study compared a commercial bio-based Rejuvenator A and a petroleum-based Rejuvenator B to reveal how chemical compositions control asphalt regeneration. Following JTG 3410-2025 standards, asphalt binders underwent extended RTFOT aging (75, 112.5, and 150 min) and were externally blended with rejuvenators at 5%, 7.5%, and 10% by binder mass. A multi-scale framework combining macro tests, interfacial characterization, SARA fraction analysis, ATR-FTIR, and molecular dynamics (MD) simulations was established. Results indicated that the two rejuvenators acted via different mechanisms. Rejuvenator B contained 31.64% saturates and restored aged asphalt mainly through physical dilution and softening. This rejuvenator formed 0–80 hydrogen bonds dominated by weak C–H···O interactions, and the corresponding rejuvenated asphalt yielded a CII of 0.293. It was effective for 75 min-aged binders yet produced more oxidation products after re-aging. Conversely, Rejuvenator A, characterized by 68.10% aromatics and 20.17% resins, exhibited a 3–5° lower equilibrium contact angle, and a roughly 13% shorter relative penetration time than Rejuvenator B. Its network of 150–250 hydrogen bonds effectively disrupted asphaltene aggregates, reducing the CII to 0.180. Consequently, Rejuvenator A successfully restored 112.5 min- and 150 min-aged asphalt with significantly lower secondary oxidation. These performance differences were governed by aromatic and polar fractions rather than feedstock origins. While quantitative findings are sample-specific, the established framework provides theoretical references for engineering rejuvenator selection and high-performance regenerant design. Full article

To mitigate high-temperature VOC emissions and reduce construction temperatures in recycled asphalt, a USP warm mix additive was introduced into waste soybean oil (WSO) recycled asphalt. This study systematically investigates the effects of USP content (1%, 3%, 5%, and 7%) and construction temperature (140 °C and 160 °C) on VOCs emission characteristics, inhibition mechanisms, and rheological performance. The results show that USP reduces total VOC emissions, with the key inhibition effect achieved at 5% USP. At 160 °C, the VOCs inhibition rate reached 39.5% at 5% USP, while at 140 °C it increased to 80.8%; the findings suggest that lower temperatures enhance the inhibitory effect. The results show USP cuts emissions via physical mechanisms. However, the significant FTIR and DSC analyses suggest that VOC reduction appears to be primarily governed by physical mechanisms, including phase-change cooling, physical encapsulation, and migration retardation, without altering the chemical structure of asphalt. Moreover, the important rheological results indicate that although USP slightly decreases the high-temperature complex modulus and rutting factor, the evidence demonstrates that it improves the percent recovery (R_0.1 from 53% to 66%; R_3.2 from 21% to 40%) and low-temperature crack resistance through decreased stiffness S and increased m-value. In light of these significant findings, the study demonstrates that USP exhibits a multi-performance balance, appearing to reduce VOC emissions and improve workability while moderately weakening high-temperature deformation resistance. Notwithstanding the reduced high-temperature resistance, the key evidence could demonstrate that USP enhances elastic recovery and low-temperature performance in the results. The optimal USP content appears to be 5%, providing the critical compromise between emission reduction and pavement performance for WSO recycled asphalt. Full article

The whole pavement life cycle is divided into five phases: raw material production, construction, service use, maintenance and rehabilitation, and end-of-life (EOL). Distinct system boundary definitions (cradle to gate, cradle to site, cradle to grave) are clearly distinguished, and two categories of vehicle-related emissions are strictly differentiated: baseline vehicle operation emissions (excluded) and pavement-induced incremental emissions (included only for full cradle-to-grave accounting). According to cited highway pavement inventory data (functional unit: 1 m² full cross-section composite pavement, cradle-to-gate material-only boundary), cement-related materials account for merely 4.7% of total structural material mass yet contribute over 84.5% of material-phase carbon emissions, while asphalt mixture construction emissions generally make up less than 10% of mixing-stage outputs. In the use phase, pavement deformation, rolling resistance elevation and surface texture loss trigger extra vehicle fuel consumption and associated greenhouse gas increments. Maintenance-stage emissions stem from repair material manufacturing, on-site machinery operation and traffic congestion delays during lane closure; milling, transportation and recycling dominate EOL carbon outputs. This review further classifies all emissions into direct engineering emissions and pavement-derived indirect emissions, compares carbon performance and service-life extension effects of eight mainstream maintenance strategies, and thoroughly decomposes milling, stockpiling, haulage and recycling links of waste asphalt, alongside multiple environmental burden allocation methods for reclaimed asphalt pavement (RAP). A full spectrum of green low-carbon technologies is summarized, including biochar bio-materials, RAP, crumb rubber, industrial byproducts, warm-mix asphalt (WMA), cold recycling and CCUS negative-carbon materials. We also balance their emission reduction benefits against potential deterioration risks to rutting resistance, fatigue life and moisture stability. Combined with a life-cycle cost assessment (LCCA), this study analyzes cost-emission trade-offs of all technical routes, and deeply discusses multi-source uncertainty, sensitive input parameters and universal methodological limitations of pavement LCA. Core takeaways indicate that raw material production and long-term service use are the two dominant carbon emission stages; a medium RAP-WMA combination and cold in-place recycling represent the most economically and environmentally balanced mitigation solutions. Major research gaps and targeted future research directions are proposed, providing standardized theoretical support and dual environmental–economic decision references for low-carbon asphalt pavement design and full-life carbon accounting. Full article

Polymer-modified asphalt has been widely used to improve pavement durability under increasing traffic loads and complex environmental conditions. Styrene–butadiene–styrene (SBS) is one of the most effective elastomer modifiers. It can form a polymer-rich network within asphalt. Styrene–methyl methacrylate copolymer-based modifier (SMC) can be produced from recycled rubber and plastic resources. It has attracted increasing attention because of its potential compatibility, processability, and environmental benefits. This paper reviews the modification mechanisms, rheological properties, fatigue performance, aging resistance, and engineering applications of SBS-, SMC-, and SMC–SBS-modified asphalt and mixtures. Particular attention is given to the synergistic effects between SBS and SMC, including polymer swelling, phase morphology, network formation, interfacial compatibility, and durability evolution. Existing studies indicate that SBS mainly improves elastic recovery and high-temperature deformation resistance. In contrast, SMC can enhance workability, low-temperature flexibility, and construction compatibility. Their composite modification shows strong potential for balancing high-temperature, low-temperature, fatigue, and aging performance. However, current studies are still limited by insufficient quantitative comparisons, unclear microstructural mechanisms, and the lack of unified evaluation methods. Future studies should establish multi-scale structure–property–durability models. The modifier dosage range should also be optimized. This review provides a systematic reference for the development of high-performance and sustainable polymer-modified asphalt materials. Full article

The modification of bitumen with recycled rubber materials has gained significant attention due to its potential to enhance pavement performance and support sustainable waste management. In this study, the rheological properties of bitumen modified with crumb rubber (CR) and devulcanized crumb rubber (DCR) were investigated. Rubber modifiers were added at concentrations of 5–25% by weight, and the rheological behavior was evaluated using a Dynamic Shear Rheometer at 1.59 Hz over a temperature range of 46–96 °C. Key parameters, including storage modulus (G′), loss modulus (G″), and complex viscosity (η*), were analyzed. The results indicate that increasing rubber content significantly enhances stiffness and viscosity, improving resistance to deformation at elevated temperatures. Moreover, DCR-modified binders exhibit higher rheological performance compared to CR systems, indicating better compatibility with the bitumen matrix. Overall, devulcanized rubber demonstrates superior efficiency as a modifier and shows strong potential for improving the durability and high-temperature performance of asphalt binders. 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 PRISMA-guided scoping review examines the use of waste materials in civil engineering as a sustainable approach to reducing environmental impacts, conserving natural resources, and supporting circular economy principles. The rapid growth of urbanization, industrialization, mining, and agricultural activities generates large amounts of waste materials, including fly ash, ground granulated blast-furnace slag, bauxite residue, mining tailings, waste rock, acid-mine drainage sludge, waste plastics, post-consumer vulcanized rubber, recycled construction materials, and agricultural ashes. The disposal of these materials often creates serious environmental and land-use problems, making their reuse increasingly important. In this context, civil engineering is one of the most promising sectors for large-scale waste valorization because of its high material demand and its ability to use different waste streams into practical applications such as concrete and cementitious systems, pavement and asphalt engineering, geotechnical works, and other infrastructure sectors. This review critically evaluates the global availability, material characteristics, engineering applications, environmental and economic benefits, recent advances, and key challenges related to major industrial, mining, agricultural, polymeric, and construction-derived wastes. Although significant progress has been made in this field, wider implementation is still limited by variations in material properties, technical and environmental challenges, economic constraints, and limited field validation of long-term performance. By bringing together current knowledge from different waste streams and civil engineering sectors, this review highlights important research gaps and future directions to support more sustainable, resilient, and resource-efficient infrastructure development. The effective use of waste materials in civil engineering can play an important role in reducing carbon emissions, improving resource efficiency, and supporting global sustainability. 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