Search Results (1,782)

To address poor interfacial compatibility between rubber powder and emulsified asphalt in cold-mixed asphalt mixtures, this study employed microwave activation to desulfurize and activate waste rubber powder. The investigation combined experimental research, molecular dynamics simulations, and solid–liquid separation methods to systematically explore the mechanism by which rubber powder activation influences cold-mixed emulsified asphalt systems. Results revealed an effective activation temperature of approximately 190 °C for rubber powder. The activation process, driven by microwave heating, involves main-chain scission and crosslink bond cleavage. Furthermore, moderate desulfurization reduces the solubility difference between rubber powder and asphalt, increases interfacial binding energy, and enhances the diffusion coefficient. Based on these findings, an optimal microwave activation scheme was proposed (4 min at 1040 W followed by 2 min at 873 W), which offers low energy consumption and excellent modification effects. Activation treatment reduces the initial viscosity by 33.9% and accelerates demulsification. Lastly, the results of molecular dynamics simulations are highly consistent with those of macroscopic experiments, forming a complete research chain of “microscopic mechanism analysis—macroscopic performance verification” and providing a theoretical basis and technical support for high-performance cold-mixed rubber-powder-modified emulsified asphalt mixtures. Full article

Skid resistance is a critical functional property of asphalt pavements and is strongly influenced by surface topography. However, existing studies often rely on limited texture indicators, making it difficult to comprehensively characterize pavement surface morphology and directly relate it to braking performance. In this study, the surface topography of eight asphalt mixtures, including six porous asphalt concrete (PAC-13) mixtures with different air-void contents, one stone mastic asphalt (SMA-13) mixture, and one asphalt concrete (AC-13) mixture, was characterized using a high-precision three-dimensional laser scanner. The acquired point-cloud data were analyzed using one-dimensional, two-dimensional, three-dimensional, and ISO 25178 surface parameters. Correlation analysis was first used to remove redundant indicators, and principal component analysis was then performed to reduce dimensionality. Three principal components explaining 67.45%, 9.94%, and 6.42% of the total variance, respectively, were extracted and combined into a comprehensive surface topography index (F). The results showed that F effectively distinguished different mixture types and PAC surfaces with different air-void levels. Field validation was further conducted on PAC, SMA, and AC pavements in Xi’an, China, and a regression model relating F to the braking distance from 60 km/h to 0 km/h (D60) was established, with an R² of 0.8864. The proposed index provides a multidimensional and practical approach for asphalt pavement surface characterization and offers a useful basis for skid-resistance evaluation and braking distance prediction. Full article

To address the slow curing and low early strength of conventional modified epoxy emulsified asphalt repair materials, this study introduced steel slag aggregate into epoxy emulsified asphalt mixtures. Experimental techniques including heat absorption–heat transfer rate tests, Marshall stability tests, COMSOL numerical simulation, and scanning electron microscopy (SEM) were adopted to analyze rapid and uniform heating under microwave radiation. The influence of steel slag’s chemical composition, content, and particle size on epoxy curing, asphalt demulsification, and early strength of the mixture was systematically examined. Results show that steel slag containing Fe and Mg elements exhibits higher microwave absorption efficiency. When its content exceeds 15%, the heating rate increases by approximately 0.335 °C/s under the tested conditions. Particles sized 0.6~2.36 mm show better wavelength matching with the applied microwave frequency (2.45 GHz), thereby enhancing absorption. After 140 s of microwave radiation, the core temperature of the mixture reaches 110 °C, which is the appropriate temperature to achieve rapid epoxy curing and synchronous asphalt demulsification. These two processes synergistically form a continuous network structure, thereby improving the compactness and initial laboratory Marshall stability of the mixture. Nevertheless, this study has several limitations. The microwave absorption efficiency depends strongly on the specific mineralogy and Fe/Mg content of steel slag, both of which may vary with source. The conclusions are based on laboratory-scale tests under fixed microwave power and mixture proportions. Despite these limitations, the results demonstrate that steel slag can serve as an effective microwave-absorbing component in epoxy emulsified asphalt mixtures, enabling rapid curing and demulsification to accelerate early strength development. Full article

The large-scale generation of asphalt dust waste (ADW) has raised increasing environmental concerns, while its high-value utilization in cementitious materials remains insufficiently explored, particularly in terms of mechanical performance, durability-related properties, and integrated sustainability evaluation. In this study, a graded utilization strategy based on particle size was proposed to incorporate ADW into alkali-activated concrete paving blocks, in which fine ADW fraction (<0.075 mm) was used as a partial replacement of blast furnace slag (BFS), while the coarser ADW fraction was used as a partial replacement of river sand, aiming at sustainable pavement applications. In addition, two types of ADW with different lithologies, namely limestone ADW and basalt ADW, along with their combined system, were investigated. The results show that the incorporation of ADW effectively enhances the engineering performance of paving blocks. The compressive strength increased from 45.3 MPa to 56.6 MPa, while water absorption decreased from 5.3% to 4.1%. All mixtures satisfied the requirements for abrasion resistance and slip resistance, demonstrating their compliance with the performance criteria for pedestrian pavement applications. Among all mixtures, the combined use of limestone ADW and basalt ADW exhibited the best overall performance. The improved performance may be attributed to the combined effects of graded particle utilization and the potential compositional complementarity between calcium-rich limestone ADW and silica–alumina-rich basalt ADW, which is consistent with the denser microstructure observed in SEM images. In addition, the proposed strategy contributes to improved solid waste utilization and reduced consumption of natural resources, as reflected in the quantitative sustainability assessment. Overall, this study demonstrates that graded utilization of ADW is a feasible approach for developing alkali-activated paving materials, with promising performance and sustainability potential. Full article

To achieve synergistic, efficient degradation of volatile, harmful gases in asphalt and to scientifically quantify inhibitor dosage, this study proposes a dosage optimization method that integrates nonlinear regression with a multi-response satisfaction function. Focusing on a proprietary composite volatile gas suppressant, we systematically measured the concentration trends of ammonia, nitrogen oxides, sulfur dioxide, and hydrogen sulfide emitted from three asphalt systems: base asphalt, SBS modified asphalt (Styrene-Butadiene-Styrene modified asphalt), and rubber modified asphalt under different suppressant dosages (0%, 0.02%, 0.04%, 0.06%, 0.08%, and 0.10%). First, high-precision prediction models (R² > 0.95) were established using nonlinear regression to relate different inhibitor dosages to corresponding gas concentrations. Based on a satisfaction function, the multi-objective degradation effects were normalized into a comprehensive satisfaction index, and the optimal dosage was then determined. The results indicate: (1) the constructed models can accurately predict the concentrations of volatile harmful gases at various dosages; (2) the predicted optimal blending ratios vary by asphalt type, specifically 0.082% for base asphalt, 0.079% for SBS modified asphalt, and 0.080% for rubber modified asphalt; and (3) at the optimal blending ratios, all four gases achieve high and balanced degradation levels, resulting in the best overall degradation performance. At the same time, road performance tests confirmed that this blending ratio has no significant negative impact on the high-temperature and low-temperature stability or water stability of the asphalt mixture. Compared with traditional single-factor empirical methods, this approach represents a methodological upgrade from qualitative description to quantitative prediction, and from single-objective comparison to multi-objective synergistic optimization, providing data and theoretical support for the precise, efficient, and engineering-applicable use of asphalt volatile gas inhibitors. Full article

The sustainable utilization of multiple reclaimed pavement materials is a critical pathway toward green highway construction. This study investigates the performance and synergistic mechanisms of cold-recycled mixtures incorporating both Reclaimed Asphalt Pavement (RAP) and Reclaimed Cement-Stabilized Base (RCSB), using emulsified asphalt as the primary binder. A comprehensive experimental program was conducted to evaluate the effects of reclaimed material proportions, mixing sequences, and curing ages on the mechanical strength, moisture susceptibility, and high-temperature stability of the mixtures. Microscopic characterization via Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) were employed to elucidate the Interfacial Transition Zone (ITZ) evolution. Results indicate that an optimal RCSB incorporation range of 20–40% establishes a robust “stone-to-stone” rigid skeleton, significantly enhancing the splitting strength (up to 0.87 MPa) and durability (Splitting Strength Ratio, TSR > 91%). SEM observations confirm the formation of a dense interpenetrating network structure within this range, where cement hydration products and asphalt films achieve optimal chemo-physical bonding. Exceeding 40% RCSB leads to a moisture-starved state and a sharp decline in dynamic stability due to insufficient binder coating. Micro-morphological characterization reveals that the transition from macro-interfacial debonding to a robust cohesive failure mode is the fundamental driver for the performance peak at 20–40% RCSB. SEM observations confirm the formation of a dense interpenetrating network structure, where cement hydration products successfully anchor into the asphalt film. This optimized ITZ effectively eliminates the stress concentration and aggregate crushing seen in high-RAP mixtures, thereby ensuring superior mechanical integrity. Furthermore, a pre-wetting mixing sequence ensures a high-energy mineral surface that promotes the heterogeneous nucleation of cement. SEM results show that this prevents the competitive adsorption between cement and asphalt, transforming the ITZ from a friable, loose state into a densified crystalline adhesive matrix. Full article

To address the pronounced degradation of skid resistance in steel bridge deck pavements exposed to hot, humid, and rainy environments, this study investigates an EA-10 epoxy–asphalt mixture and proposes a gradation design method with skid resistance as the primary performance objective. An orthogonal experimental design was employed to systematically analyze different combinations of sieve passing rates, and after determining an optimum asphalt–aggregate ratio of 6.25%, the skid resistance of the mixtures under various service conditions was evaluated using macrotexture depth, dry friction coefficient, and water-film friction coefficient. The results demonstrate that the formation of skid resistance follows a mechanism in which the macroscopic framework and microscopic pores interact synergistically. The passing rate of the 4.75 mm sieve is the dominant factor governing macrotexture depth, while the 0.3 mm sieve plays a critical regulating role in texture development; meanwhile, the passing rates of the 2.36 mm and 0.6 mm sieves exert a decisive influence on both dry and water-film friction coefficients. When the passing rates of the 4.75 mm, 0.3 mm, 2.36 mm, and 0.6 mm sieves are approximately 70%, 26.5%, 58–61%, and 34%, respectively, the mixture exhibits superior overall skid-resistance performance. Based on the evaluation results of the International Friction Index (IFI), the optimized gradation shows a more stable level of skid resistance under wet and slippery conditions. These findings provide quantitative evidence and engineering guidance for the skid-resistance-oriented gradation design of epoxy–asphalt mixtures used in steel bridge deck pavements in hot and humid regions. Full article

The paper introduces a non-linear method for modeling the luminance coefficient (Qd) of asphalt (bituminous) mixtures using a Generalized Additive Model (GAM). Developed from observations after three and six months of service, the model accounts for the effects of aggregate luminance, binder content, and air voids, as well as temporal and non-linear dependencies. It showed a high goodness-of-fit (R² = 0.91) and strong predictive accuracy (RMSE = 4.8 mcd/m²/lx). The analysis revealed that the service period significantly influences luminance, with values after six months being, on average, 12.6 mcd/m²/lx higher than at three months. The impact of aggregate luminance was non-linear, displaying a saturation effect, while asphalt content and air voids varied in their influence over time. Results indicate that the factors affecting bituminous mixture luminance are complex and vary over time; moreover, high aggregate luminance alone does not guarantee a high Qd. Applying the additive model confirms the importance of accounting for non-linear effects and temporal interactions when assessing road surface optical properties. Full article

Semi-circular bending tests were conducted on high-elasticity asphalt concrete under different aging conditions to investigate the effects of rubber particles and polyester fiber contents on its fracture properties. Results showed that the incorporation of approximately 3% rubber particles increased the fracture energy by 15%, whereas the addition of 1.2% polyester fibers increased the fracture toughness and fracture energy by 4% and 19%, respectively. Aging-induced oxidative hardening enhanced the overall elastic modulus and interfacial constraint effect of the asphalt mixture, thereby improving the stress transfer efficiency among the rubber particles, polyester fibers, and the surrounding matrix. As a result, both the peak load and fracture toughness increased. However, compared with the unaged state, aged asphalt concrete became more susceptible to brittle fracture, with a decrease in fracture energy and a change in the crack propagation path from a curved to a straight trajectory. Full article

Rapid urbanization has intensified challenges regarding urban waterlogging and vehicle exhaust pollution. While permeable asphalt mixtures mitigate waterlogging and nano-TiO₂ offers photocatalytic exhaust degradation capabilities, the direct application of nano-TiO₂ is hindered by agglomeration and low photocatalytic efficiency. This study developed a composite modified nano-TiO₂ via metal ion doping and support treatment to enhance its performance in asphalt pavements. Specifically, nano-TiO₂ was doped with Fe³⁺, Ag⁺, and La³⁺ via the sol–gel method, and supported on activated carbon (AC) or Al₂O₃. The exhaust degradation performance was evaluated using a custom-built system, while dispersion properties were assessed via fluorescence microscopy and UV-Vis spectrophotometry. Furthermore, X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy were conducted to investigate the microstructural mechanisms underlying the doping modification and support treatment. Photocatalytic permeable asphalt mixtures were prepared by partially replacing mineral powder with the composite modified nano-TiO₂ to validate exhaust degradation and pavement performance. The results indicated that metal doping substituted Ti⁴⁺ in the lattice, inducing defects and reducing crystallite size to boost photocatalytic activity. The optimal doping concentrations are determined to be 1.0% for Fe³⁺, 1.5% for Ag⁺, and 1.0% for La³⁺. Among these, Fe³⁺-doped nano-TiO₂ at 1.0% content exhibits superior exhaust degradation, achieving 46.7% efficiency for hydrocarbons (HC) and 33.5% for nitrogen oxides (NO). Regarding dispersion, while AC performs better at low support content, Al₂O₃ at 40% content provides superior dispersion properties by increasing active sites and surface hydroxyl groups. For photocatalytic permeable asphalt mixtures, replacing 40–50% of mineral filler with the composite modifier is recommended. The optimized mixture demonstrates superior exhaust degradation performance while maintaining the required high-temperature stability, low-temperature cracking resistance, water stability, and fatigue life. Specifically, compared to the control group, these indicators for the mixture with 50% of the mineral filler replaced by the composite modifier increases by 7.0%, 12.5%, 13.4%, and 22.9%, respectively. This study presents a viable technical solution for developing multifunctional asphalt mixtures with photocatalytic functionality as the core innovation and mechanical performance as the application baseline. Full article

To address the issues of high energy consumption and unstable construction quality caused by high-temperature heating during the preparation of traditional hot-mixed/grouted semi-flexible pavement (SFP) mixtures, a cold-mixed integrated (CMI) process was proposed. In addition, the material composition of the mixtures was optimized. The effects of the preparation process and binder type on the high- and low-temperature performance, water stability, and fatigue performance were then analyzed. Furthermore, the microstructural characteristics of the semi-flexible mixture were also investigated. The results indicated that the CMI process facilitated the formation and uniform distribution of calcium silicate hydrate (C-S-H), enhanced the binder’s ability to encapsulate aggregates and fill skeletal voids, significantly reduced the mixture’s void ratio, and improved its pavement performance. The proposed procedure was a means of enhancing high-temperature stability and fatigue life (an increase of 80% and 200 times compared to the hot-mixed/grouted (HMG) process, and 5 times and 300 times compared to AC-13, respectively). Compared with the HMG process, the CMI process offered greater advantages in enhancing the high-temperature stability and fatigue resistance of the mixture, particularly when using SBS-modified asphalt, where fatigue performance exhibited an order-of-magnitude improvement. Furthermore, while SBS modification could improve the road performance of SFP materials, mixtures prepared with SBS-modified emulsified asphalt demonstrated more significant enhancements in high-temperature stability and fatigue resistance, approximately 2 times and 10 times higher than SBS-modified mixtures, respectively. The addition of styrene–acrylic emulsion (SAE) could further enhance the low-temperature crack resistance by approximately 7%. The research results can provide a reference for the development and application of preparation processes for semi-flexible mixtures. Full article

The disposal of waste tyres presents a significant environmental challenge, necessitating sustainable, high-value recycling solutions. This study explores the incorporation of waste tyre metal fibre (WTMF) into hot mix asphalt (HMA) to enhance mechanical performance while reducing its electrical resistivity as well as the landfill burden. The primary goal of this research is to apply response surface methodology (RSM) to experimental data for modelling and optimizing WTMF-modified HMA mixes by capturing the coupled effects of fibre reinforcement and binder content on mechanical and functional performance. The microstructural characteristics of WTMF were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). WTMF-modified mixes containing five WTMF dosages (from 0% to 1.50%) and bitumen contents from 4% to 6% were prepared and tested in the laboratory. The resulting dataset was used for RSM modelling, with WTMF and bitumen contents as input factors and Marshall stability, flow, porosity, and electrical resistivity as response variables. The central composite design (CCD) technique was employed to quantify interaction effects and to identify statistically significant trends. The developed models were validated using statistical indicators, and optimal mixture compositions were determined and experimentally verified. Microstructural analysis revealed WTMF’s irregular, rough surface with microcracks and pits, aiding crack-bridging and stress transfer. RSM results indicated 0.71% WTMF and 5.1% bitumen as an optimal combination of factors. Furthermore, high R² (>0.80) and adequate precision (>4.0) values from analysis of variance (ANOVA) underscore the significance of the proposed models, revealing a robust correlation between experimental and predicted data. This study demonstrated WTMF’s potential to be used in conventional HMA mixes, offering a sustainable recycling pathway for waste tyres. Full article

Asphalt pavement on rigid base (cement concrete) differs significantly from traditional granular base pavement. To investigate its mechanical behavior, a viscoelastic–viscoplastic damage constitutive model for asphalt mixtures is proposed and verified. A user-material subroutine (UMAT) is developed to implement the model, and a three-dimensional finite element model is established to analyze pavement responses under various working conditions. Key numerical results include the following: the asphalt layer primarily experiences compressive–shear failure, with peak shear stress (τ₁₂) reaching 141.6 kPa under rigid base conditions; emergency braking increases τ₁₂ to approximately 270.3 kPa, a 91% increase; increasing vehicle speed from 15 m/s to 35 m/s raises τ₁₂ by 36.7%; based on stress analysis alone, the recommended asphalt layer thickness is between 0.10 m and 0.14 m, as thickness beyond 0.10 m yields diminishing stress reduction. The findings provide references for performance prediction, structural design, and material development of asphalt pavement on a rigid base. Full article

Warm-mix asphalt (WMA) technology and basalt fiber modification have been increasingly applied in road engineering. However, conventional basalt fibers often disperse unevenly and tend to agglomerate. In this study, basalt fiber powder (BFP) was incorporated into a Sasobit-based WMA system and systematically compared with matrix asphalt, Sasobit-modified WMA, conventional basalt fiber-modified WMA, and styrene butadiene styrene (SBS)-modified asphalt. Multiscale characterization—including dynamic shear rheometry (DSR), bending beam rheometry (BBR), scanning electron microscopy (SEM), and nanoindentation—was conducted to elucidate rheological behavior and interfacial micromechanical responses. The corresponding Asphalt Concrete-13 (AC-13) mixtures were further evaluated through rutting tests, low-temperature bending tests, and moisture susceptibility tests. Results demonstrate that micronized BFP achieves more homogeneous dispersion within the asphalt matrix and may promote a more effective reinforcing morphology, significantly enhancing high-temperature deformation resistance while partially mitigating the low-temperature stiffness increase induced by Sasobit. Compared with conventional basalt fiber systems, BFP shows better stress relaxation capacity and interfacial mechanical response under the tested conditions. At the mixture level, the BFP–Sasobit system showed the best overall performance, with the dynamic stability increasing by 242.2% relative to the base asphalt mixture and the residual Marshall stability reaching 92.3%, while the low-temperature flexural strain increased by 33.3%. Overall, the findings suggest that morphology-controlled micronization provides a morphology-guided enhancement strategy for Sasobit-based warm-mix asphalt by promoting coordinated improvements across the rheological, micromechanical, and mixture scales. Full article