Search Results (25)

With the rising performance demands in road engineering, traditional experiments often fail to reveal the microscopic mechanisms behind asphalt behavior. Molecular dynamics (MD) simulation has emerged as a valuable complement, enabling molecular-level insights into asphalt’s composition, structure, and aging mechanisms. This review summarizes the recent advances in applying MD to asphalt research. It first outlines molecular model construction approaches, including average models, three- and four-component systems, and modified models incorporating SBS, SBR, PU, PE, and asphalt–aggregate interfaces. It then analyzes how MD reveals the key performance aspects—such as high-temperature stability, low-temperature flexibility, self-healing behavior, aging processes, and interfacial adhesion—by capturing the molecular interactions. While MD offers significant advantages, challenges remain: idealized modeling, high computational demands, limited chemical reaction simulation, and difficulties in multi-scale coupling. This paper aims to provide theoretical insights and methodological support for future studies on asphalt performance and highlights MD simulation as a promising tool in pavement material science. Full article

Asphalt pavement cracking is an important factor affecting its service life. Under certain conditions, the self-healing behavior of asphalt itself can repair pavement cracks. However, the self-healing ability of asphalt itself is limited. In order to strengthen the self-healing ability of asphalt, the microcapsule wrapped with a repair agent is pre-mixed into the asphalt mixture. When the crack occurs and spreads to the surface of the microcapsule, the microcapsule ruptures and the healing agent flows out to realize the self-healing of the crack. Current microcapsules are mostly prepared with healing agents and bio-oil as core materials, and their high-temperature resistance to rutting is poor. While the epoxy resin contains a three-membered cyclic ether, it can undergo ring-opening polymerization to bond and repair the asphalt matrix. In addition, research on microcapsules mainly focuses on the self-healing properties of microcapsule-modified asphalt. In fact, before adding microcapsules to asphalt to improve its self-healing performance, it is necessary to ensure that the asphalt has a good road performance. On this basis, the self-healing performance of asphalt is improved, thereby extending the service life of asphalt pavement. Therefore, two-component epoxy self-healing microcapsules (E-mic and G-mic) were first prepared in this paper. Then, a temperature scanning test, rheological test of bending beams, and linear amplitude scanning test were, respectively, conducted for the microcapsule/asphalt to evaluate its road performance, including the high-temperature performance, low-temperature crack resistance, and fatigue performance. Finally, the self-healing performance of microcapsules/asphalt was tested. The results showed that the self-developed epoxy self-healing microcapsules were well encapsulated and presented as spherical micron-sized particles. The average particle size of the E-mic was approximately 23.582 μm, while the average particle size of the G-mic was approximately 22.440 μm, exhibiting a good normal distribution. In addition, they can remain intact and unbroken under high-temperature conditions. The results of road performance tests indicated that the microcapsule/asphalt mixture exhibits an excellent high-temperature resistance to permanent deformation, low-temperature crack resistance, and fatigue resistance. The self-healing test demonstrated that the microcapsule/asphalt exhibited an excellent self-healing performance. When the microcapsule content was 4%, the self-healing rate reached its optimal level of 67.8%, which was 149.2% higher than that of the base asphalt. Full article

Asphalt pavements face escalating challenges from traffic loading, climate change, and material degradation, necessitating innovative maintenance solutions. Thermally induced self-healing technologies, leveraging the viscoelastic properties of asphalt binders, can autonomously repair microcracks through targeted thermal activation. This review explored thermally induced self-healing in asphalt mixtures, with a focus on leveraging steel slag as a functional aggregate to enhance sustainability and durability. Two thermal-activation methods, electromagnetic induction and microwave heating, were critically analyzed, highlighting their distinct advantages in heating efficiency, depth, and uniformity. Steel slag offers dual benefits: improving mechanical interlock and skid resistance in mixtures while facilitating efficient heat generation via electromagnetic induction or microwave heating. However, challenges such as hydration-induced expansion, heterogeneous slag composition, and energy-intensive heating processes impede widespread adoption. Pretreatment methods, including natural aging, carbonation, and surface modifications, are essential to mitigate volumetric instability and optimize slag performance. Key factors influencing healing efficacy, including binder properties, operational parameters (e.g., microwave power, frequency), and environmental trade-offs, were systematically evaluated. Future research directions emphasized standardized pretreatment protocols, hybrid heating technologies for uniform temperature distribution, and smart-infrastructure integration for predictive maintenance. Full article

The harsh environments in saline–alkaline areas and high-altitude regions with intense ultraviolet radiation pose great challenges to the durability of asphalt pavements. The fatigue performance of asphalt binder significantly determines the actual service life of asphalt pavements. Existing studies have predominantly focused on the impact of individual environmental factors (e.g., aging and saline–alkaline erosion) on asphalt performance, yet there remains a notable research gap in the systematic analysis of asphalt’s fatigue and self-healing behavior under coupled multi-factor interactions, particularly regarding the synergistic effects of UV aging and saline–alkaline conditions. Therefore, it is of great importance to understand the influence rules of the coupling effect of aging and salt–alkaline characteristics on the properties of asphalt materials. In this study, 70# base asphalt and GO-modified asphalt were taken as the research objects. Frequency sweep tests, linear amplitude sweep (LAS) tests, and LAS-based healing tests were conducted using a dynamic shear rheometer. The fatigue and self-healing properties of the two asphalt materials under different aging conditions and aging and salt–alkali coupling effects were analyzed based on the viscoelastic continuum damage theory. The results showed that the degree of aging can increase the stress peak of asphalt materials under small strains and also increase their stress attenuation rate. Except for short-term aging and salt–alkali effects, the aging and salt–alkali coupling effects generally further reduce the stress peaks of asphalt materials. Aging can increase the fatigue life of asphalt and increase the fatigue life attenuation rate of asphalt. The aging and salt–alkali coupling effects will reduce the fatigue life of asphalt and increase the decline rate of the asphalt fatigue life. The self-healing efficiency of asphalt is affected by the degree of aging, and the aging and salt–alkali coupling effects further reduce the self-healing efficiency of asphalt materials. This paper elucidates the influence mechanisms of intense UV irradiation and saline–alkaline environments on GO-modified asphalt, providing theoretical and practical references for its future engineering applications in harsh environmental conditions. Full article

The increasing global demand for metals, driven by technological progress and the energy transition, has led to an acceleration in the expansion of the mining and metallurgical industry, resulting in an increase in the generation of mine tailings. This waste, which is of heterogeneous composition and has high contaminant potential, represents significant environmental and social challenges, affecting soils, water, and the geotechnical stability of tailings. The accumulation of these mine tailings poses a problem not only in terms of quantity, but also in terms of physicochemical composition, which exacerbates their environmental impact due to the release of heavy metals, affecting ecosystems and nearby communities. This article reviews the potential of geopolymerization and 3D printing as a technological solution for the management of tailings, offering an effective alternative for their reuse as sustainable building materials. Alkaline activation of aluminosilicates facilitates the formation of N–A–S–H and C–A–S–H cementitious structures, thereby providing enhanced mechanical strength and chemical stability. Conversely, 3D printing optimizes structural design and minimizes material consumption, thereby aligning with the principles of a circular eco-economy and facilitating carbon footprint mitigation. The present study sets out to compare different types of tailings and their influence on geopolymer reactivity, workability, and mechanical performance. In order to achieve this, the study analyses factors such as the Si/Al ratio, rheology, and setting. In addition, the impact of alkaline activators, additives, and nanoparticles on the extrusion and interlaminar cohesion of 3D printed geopolymers is evaluated. These are key aspects of their industrial application. A bibliometric analysis was conducted, which revealed the growth of research in this field, highlighting advances in optimized formulations, encapsulation of hazardous waste, CO₂ capture, and self-healing geopolymers. The analysis also identified technical and regulatory challenges to scalability, emphasizing the necessity to standardize methodologies and assess the life cycle of materials. The findings indicated that 3D printing with tailings-derived geopolymers is a viable alternative for sustainable construction, with applications in pavements, prefabricated elements, and materials resistant to extreme environments. This technology not only reduces mining waste but also promotes the circular economy and decarbonization in the construction industry. Full article

In recent years, the employment of rejuvenators and warm mix asphalt (WMA) additives for reclaimed asphalt pavement (RAP) has been recognized as a popular approach to increase the recycling rate of waste materials and promote the sustainable development of pavement engineering. However, the composition of warm mix recycled asphalt binder is complicated, and the microstructural changes brought about by the rejuvenators and WMA additives are critical in determining its macroscopic mechanical properties. This research focuses on the atomic modeling of the rejuvenators and WMA additives diffusion behavior of the warm mix recycled asphalt binder. The objective is to reveal the thermodynamic performance and diffusion mechanism of the WMA binder under the dual presence of rejuvenators and WMA additives. Three types of mutual diffusion systems (Aged and oil + virgin + wax, Aged + virgin + wax, and Aged and oil + virgin) were established, respectively, for a comparative investigation of the glass transition temperature, viscosity, thermodynamics, free volume, and diffusion behavior. The results indicate a 44.27% and 31.33% decrease in the glass transition temperature and apparent viscosity, respectively, after the incorporation of 5% oil rejuvenators in the Aged + virgin + wax asphalt binder, demonstrating the improved cracking resistance and construction workability. The presence of the RAP binder and organic WMA additives raised the cohesion of the asphalt binder and decreased self-healing ability and free volume, and these detrimental influences can be offset by the introduction of rejuvenators. The combined use of rejuvenators and organic WMA additives remarkably enhanced the de-agglomeration to asphaltenes, stimulated the activity of aged RAP macromolecular components, and ultimately improved the blending efficiency of virgin binders with the overall structure of RAP binders. Full article

In recent years, self-healing, ultra-thin overlay has been recognized as an advanced technology and gradually applied in asphalt pavement maintenance, but its sustainability has not been well addressed quantitatively regarding practical maintenance projects. This study utilizes steel fiber as a media-induction material for self-healing, ultra-thin overlay and verifies its integrative benefits in terms of carbon emissions and economic costs from a six-year life-cycle perspective. The system framework and research boundary were developed to include the material extraction, on-site construction, later maintenance, and demolition phases. Meanwhile, carbon emissions and economic cost inventories were established through investigations of the test section of a maintenance project. The results indicated that self-healing, ultra-thin overlay could have benefits, with a reduction of 59.43% carbon emissions and 73.15% economic costs in the six-year life cycle, during which the material extraction phase generated over 50% of the carbon emissions and economic costs in self-healing, ultra-thin overlay due to the addition of steel fiber. Comparatively, the later maintenance phase caused the most environmental and financial impacts, with over half of the carbon emissions and costs. The obtained results could act as significant reference material for the sustainable maintenance implementation of asphalt pavement. Full article

Fatigue performance and self-repairing activity of asphalt binders are two properties that highly influence the fatigue cracking response of asphalt pavement. There are still numerous gaps in knowledge to fill linked with these two characteristics. For instance, current parameters fail to accommodate these two bitumen phenomena fully. This study aims to propose a new procedure to address this issue utilizing the linear amplitude sweep (LAS) test, LAS with rest period (RP) (LASH) test, and simplified viscoelastic continuum damage (S-VECD) model. This research work used four different types of asphalt binders: neat asphalt (NA), self-healing thermoplastic polyurethane (STPU)-modified bitumen (STPB), self-healing poly (dimethyl siloxane) crosslinked with urea bond (IPA1w)-modified bitumen (IPAB), and styrene–butadiene–styrene (SBS)-modified bitumen (SBSB). Before the testing process, all the materials were subjected to short-term and long-term aging. The new procedure showed a superior capacity to analyze and accommodate all bitumen fatigue performances and self-repairing activities compared to the current method. Another finding proved that asphalt binders with a higher self-restoration behavior failed to show a better fatigue performance. Moreover, the higher fatigue performance increments produced by STPU and IPA1w in NA concerning the control bitumen were 123.7% and 143.7%, respectively. Those values were obtained with 1.0% STPU and 0.5% IPA1w in NA. A breakthrough finding demonstrated that asphalt binder fatigue response is augmented when the RP was applied at a higher damage intensity (S) value. STPB and IPAB reached their highest increments of fatigue response, containing 1.0% of STPU and 0.5% of IPA1w, respectively. Those augmentations were 207.54% and 232.64%, respectively. Full article

As a green and low-carbon road material, warm-mix rubber asphalt (WMRA) has received extensive attention from scholars for its road performance. In the in-depth study of its properties, the fatigue characteristics of WMRA are particularly critical. However, in current studies on asphalt fatigue performance, its self-healing ability is often underestimated or neglected. Furthermore, the simplified viscoelastic continuum damage theory (S-VECD), with its accuracy, speed, and convenience, provides a powerful tool for analyzing asphalt fatigue performance. Therefore, to analyze the fatigue and self-healing performances of WMRA in practical applications, four sample materials were selected in this study: virgin asphalt mastic (VAM), rubber asphalt mastic (RAM), Sasobit rubber asphalt mastic (SRAM), and Evotherm rubber asphalt mastic (ERAM). Subsequently, the samples were subjected to a comprehensive experimental design with frequency sweep tests, linear amplitude sweep tests, and multiple intermittent loading time sweep tests under different aging conditions. The fatigue and self-healing performances of different aging degrees and different types of WMRA were evaluated based on the S-VECD theory. The results show that aging reduces the fatigue and self-healing performances of asphalt mastic to a certain extent, and at a 7% strain, the fatigue life of SRAM after long-term aging is only 30.7% of the life of the unaged sample. The greater the aging degree, the more pronounced the effect. Under different aging levels, the warm-mix agent can significantly improve the fatigue and self-healing performances of rubber asphalt mastic. After undergoing ten fatigue intermittent loading tests, the recovery rate of the complex shear modulus for the long-term aged VAM was 0.65, which is lower than that of SRAM under the same conditions, and the warm mix can further extend the fatigue life of rubber asphalt by improving the self-healing properties of the asphalt. The role of Sasobit in enhancing the fatigue and self-healing performances of rubber asphalt mastic is more significant. This study can provide a theoretical basis for the promotion and application of WMRA pavements and contribute to the sustainable development of road construction. Full article

Microwave maintenance technology, as a new development trend, can realize the environmentally noninvasive and rapid repair of asphalt pavement and gradually replace traditional maintenance methods. Iron tailings were used as a self-healing material in this study to investigate the temperature response matching of microwave maintenance technology. Firstly, the physical properties and the mechanism of iron tailings were elaborated through macroscopic physical index testing and microscopic X-ray diffraction (XRD) analysis. Secondly, the applicability of aggregates to microwave heating was demonstrated by analyzing the temperature rise characteristics of the granules using infrared imaging. Then, the temperature field variation rules of the iron tailing asphalt mixture were summarized by microwave heating Marshall specimens. Finally, the road performance was assessed by conducting high-temperature dynamic stability, low-temperature tensile, water immersion Marshall, and freeze-thaw splitting tests. The experimental results showed that the iron tailings can be used as an aggregate for high-grade asphalt pavement and as the preferred aggregate for microwave maintenance technology. The iron tailings temperature field was radial from the inside out to provide different temperature response states for different pavement diseases, so the asphalt was dissolved and precipitated in a short time. The particle size of iron tailings was inversely proportional to the wave-absorbing heating rate, and the heating efficiency of the small particle size (0–4.75 mm) was the highest. The specimens doped with 4.75–13.2 mm iron tailings showed the best heating performance and road performance, with the average surface temperature of the specimens reaching 126.0 °C within 2 min. In summary, according to different disease types and construction needs, iron tailings can be used as an aggregate for asphalt pavement, providing an appropriate temperature field and improving the efficiency of the microwave maintenance of asphalt pavements. Full article

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. Full article

The preparation and application of microcapsules containing healing agents have become a crucial way to enhance the self-healing capability of bitumen. This intelligent material has become a hot topic in the field of pavement material and has greatly stimulated the development and applications of pavement engineering. However, there has been no research focused on the relationship of the multistructures from the viewpoint of molecular-size, microsize, and macrosize, which significantly limits the predictions of the self-healing efficiency and structure design of this self-healing material. The purpose of this study was to make a mathematical analysis of the influencing factors of self-healing efficiency based on the self-healing mechanism of bitumen using microcapsules, fully considering the structural dimensions, preparation conditions, and self-healing conditions. In the mathematical analysis, the cross-linking degree of the shell material molecules of the microcapsules was considered for its damage strength from the perspective of molecular structure. The final tip stress of the microcrack was believed to be equal to the puncture strength of the microcapsules in terms of microsize. From a macroscale point of view, the amount of healing agent released from the microcapsule rupture was considered more significant than or equal to the volume of the microcracks. At the same time, the time–temperature superposition principle was applied to simplify the influence factors. The above derivation based on multiscale structures found that the additive amount of the microcapsules, temperature, and time were the three main influencing factors on the self-healing features of bitumen. Finally, the experimental data was investigated considering the three factors, which thoroughly verified the feasibility of the derivation. All results will help to establish a bridge between the initial structural design of self-healing bitumen and the prediction of the final self-healing effects. Full article

One of the most roller cement concrete pavement failures of pavement is the formation of first cracks. The roughness of its completed surface after the installation has restricted the usage of this pavement. Therefore, engineers increase the quality of service of this pavement by placing a layer of asphalt coating; The primary goal of this study is to evaluate the impact of particle size and type of chip seal aggregates on filling cracks in rolled concrete pavement. Accordingly, rolled concrete samples with chip seal covering were prepared with various aggregates (limestone, steel slag, and copper slag). Then, the influence of temperature on its self-healing ability was tested by putting the samples in the microwave device for cracking improvements. With the aid of Design Expert Software and image processing, the Response Surface Method reviewed the data analysis. Even though due to the study’s limitations, a constant mixing design was applied, the results of this study indicate that the amount of crack filling and repair in specimens slag is higher than that of aggregate materials. With the increase of steel and copper slag, 50% of repair and crack repair at 30 °C, the temperature is 27.13% and 28.79%, respectively, and at 60 °C, the temperature is 58.7% and 59.4%, respectively. Full article

Fatigue cracking is a common form of flexible pavement distress, which generally starts and spreads through bitumen. To address this issue, self-healing elastomer (SHE) modified bitumens were elaborated to assess whether these novel materials can overcome the neat asphalt (NA) fatigue performance and whether the current failure definition, failure criterion, and fatigue-restoration criteria can fit their performance. All bitumens were subjected to short-term and long-term aging. Linear amplitude sweep (LAS) test, LAS with rest period (LASH), and simplified viscoelastic-continuum-damage (S-VECD) model were utilized to appraise the behavior of the mentioned bitumens. The results showed that maximum stored pseudo-strain energy (PSE) and tau ($\tau$) × N (number of loading cycles) failure definitions exhibited high efficiency to accommodate the fatigue life of NA and SHE-modified bitumens. Both failure criteria identified that SHE-modified bitumen (containing 1% of SHE) showed the highest increment of fatigue performance (67.1%) concerning NA. The failure criterion based on total released PSE, in terms of the area under the released PSE curve, was the only failure concept with high efficiency (R² up to 0.999) to predict asphalt binder fatigue life. As well, the current framework to evaluate bitumen self-restoration failed to fully accommodate asphalt binder behavior, because bitumen with higher restoration could not exhibit greater fatigue performance. Consequently, a new procedure to assess this property including fatigue behavior was proposed, showing consistent results, and confirming that SHE-modified bitumen (containing 1% of SHE) exhibited the highest increment of fatigue performance (154.02%) after application of the rest period. Hence, the optimum SHE content in NA was 1%. Furthermore, it was found that a greater number of loading cycles to failure ($N_f$) did not ensure better fatigue performance and stored PSE influenced the bitumen fatigue behavior. Full article

Concrete structures cannot efficiently perform their functions over time due to chemical and physical external effects. Thus, enhancing the relationship between repair and aged structures, and also improving the durability properties of concrete is crucial in terms of sustainability. However, high costs, negative environmental effects, and incompatibility problems occur in repair/retrofit applications. Furthermore, three-quarters of the failures in the repaired/retrofitted structures are caused by a lack of repair durability. The need for repair in pavement/bridge decks is also frequently encountered, and early-age performance problems with repair materials cause pavement/bridge decks to be unavailable for certain periods of time. Engineered Cementitious Composite (ECC) can be effectively used as repair/retrofit and pavement/bridge deck material. It also has a minimal need for repair/retrofit thanks to its high durability properties. This article presents state-of-the-art research regarding the application of ECC as a repair/retrofit and pavement/bridge deck material. Studies in the literature show that the repair/retrofit properties of ECC outperform conventional concrete and steel fiber-reinforced concrete. ECC can be a solution to high early strength and drying shrinkage problems frequently encountered in the use of repair materials. It could also be used for different repair applications such as cast, sprayed, and trenchless rehabilitation. Moreover, ECC might fulfill specific requirements for pavement, pavement overlay, tunnel pavement, airfield pavement, and bridge deck. These superior performances are attributed to ECC’s kink-crack trapping mechanism, uniquely large inelastic strain capacity, strain hardening, high tensile strain capacity, and multiple microcracking and ductile behaviors, especially bonding behavior and self-healing. Full article