Asphalt fumes released at high temperatures significantly impact human health and the natural environment. This study systematically investigated the microstructure and compositional characteristics of tea stalk biochar (TB) from pyrolysis at different temperatures (300℃, 400℃, 500℃, and 600℃) and its adsorption capacity for asphalt fumes. Scanning electron microscopy and Brunauer-Emmett-Teller analysis indicated that increasing pyrolysis temperatures enhanced the porosity and BET surface area of TB, transitioning its structure from dense and low-porosity to highly porous. Fourier-transform infrared spectroscopy and elemental analysis revealed that higher temperatures promoted biochar graphitization, reduced oxygen-containing functional groups, and increased hydrophobicity and aromaticity. Analysis of asphalt fumes demonstrated that adding 1 % TB significantly reduced asphalt fume emissions, including VOCs, H₂S, SO₂, and NOₓ. TB prepared at 500℃ (500TB) exhibited optimal adsorption, reducing VOCs by 68.6 % and H₂S by 87.5 %. GC-MS analysis further revealed that 1 % 500TB reduced aliphatic hydrocarbons, aromatic compounds, oxygen-containing compounds, and sulfur-containing compounds in asphalt VOCs by 63 %, 69 %, 67.2 %, and 63.3 %, respectively. The superior adsorption performance of 500TB was attributed to its larger surface area, diverse mesoporous structure, and high aromatic carbon content, enhancing its affinity for pollutants. Physical tests indicated that biochar enhances the thermal stability and deformation resistance of asphalt by increasing its softening point, viscosity, and penetration index, while maintaining acceptable ductility. These findings demonstrate the effectiveness of TB for mitigating asphalt fume emissions.

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Utilizing industrial solid waste as supplementary cementitious materials (SCMs) in the production of pre-stressed high-strength concrete (PHC) pipe piles can reduce the consumption of cement, thereby promoting the sustainable development of the pipe pile industry. This study focused on optimizing the use of composite SCMs including ground quartz sand (GQS) and steel slag powder (SSP) to enhance the mechanical properties and durability of PHC pipe pile concrete. The effects of GQS and SSP on the reaction products, microstructure, pore structure, mechanical properties and durability of PHC pipe pile concrete were investigated. Experimental results showed that due to the filling effect and pozzolanic effect of GQS and SSP, composite SCMs not only improves the microstructure of the interfacial transition zone between paste and aggregates in PHC pipe pile concrete, but also reduces the porosity of concrete and improves its pore structure, thereby enhancing the compressive strength and durability of concrete. When the GQS content is 20 % and the SSP content is 10 %, compared to the control group with 100 % cement, the concrete's porosity decreased by 19.3 %, the chloride ion diffusion coefficient decreased by 47.1 %, and the compressive strength increased by 3.4 %. The findings of this study provide a scientific basis for the resource utilization of steel slag and offer theoretical support for the low-carbon and sustainable development of PHC pipe pile industry.

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Generally, rejuvenators are used to supply missing components of aged asphalt, reverse the aging process, and are widely used in asphalt maintenance and recycling. However, compared with traditional rejuvenators, bio-oil rejuvenators are environmentally friendly, economical and efficient. This study looks into the effect of the three different bio-oils, namely sunflower oil, soybean oil, and palm oil, on the physical properties, rheological properties and chemical components of aged asphalt at different dosages. The asphalt physical properties and Dynamic Shear Rheological (DSR) test results show that with the increase in bio-oil, the physical properties and rheological properties of rejuvenated asphalt are close to those of virgin asphalt, but the high-temperature rutting resistance needs to be further improved. The results of Fourier Transform Infrared Spectroscopy (FTIR) show that the carbonyl and sulfoxide indices of rejuvenated asphalt are much lower than those of aged asphalt. Moreover, the rejuvenation efficiency of aged asphalt mixed with sunflower oil is better than that with soybean oil and palm oil at the same dosage. @en

This study characterized the morphology, high-temperature property, rheological property, adhesion, cohesion, and chemical component of asphalt binder under aqueous solutions of different pH values. Then the physicochemical properties of asphalt binder were comprehensively evaluated by the improved radar chart. The properties of asphalt binder stripped layer-by-layer were explored to elucidate its gradient damage behaviors. The results indicate that the pH 3 solution reveals the greatest impact on the morphology of 90 asphalt (90 A) and styrene-butadiene-styrene modified asphalt (SBS MA), leading to the wide cracks on 90 A and the network cracks on SBS MA. The comprehensive assessment index of 90 A exposed to pH 3, pH 5, pH 7, pH 9, and pH 11 solutions can be reduced by 20.8%, 20.2%, 1.5%, 14.0%, and 25.5%, respectively. While for SBS MA, its corresponding values variation are 23.2%, 17.7%, 4.6%, 8.7%, and 13.0%, respectively. The acid solutions significantly affect the comprehensive properties of 90 A, but their pH value has little effect. 90 A exposure to the higher pH value of alkali solution reveals the worse comprehensive properties. Acid solute and alkali solute can aggravate the effect of aqueous solution on the comprehensive properties of SBS MA, and the degree of aggravation increases with the increase of solute concentration. The properties of asphalt binders exhibit varied gradient damage behaviors under different solute environments. The most serious damage occurs at 25–50 µm of 90 A and 0–50 µm of SBS MA. This study facilitates an accurate understanding of the mechanism of pavement distresses and composition design and construction utilization of asphalt binders.

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9,10-Dihydro-9-oxa-10-phosphorophenanthrene-10-oxide (DOPO), recognized for its role as an efficacious fume suppressant, has been shown to mitigate the emission of noxious vapors emanating from asphalt. However, the comprehensive influence of DOPO on the composition and properties of asphalt had remained unexplored. This study embarked on an in-depth examination of the effects of various DOPO dosages on the chemical composition of asphalt, employing hydrogen nuclear magnetic resonance spectroscopy (¹H NMR) alongside an exhaustive analysis of asphalt components. Furthermore, the investigation elucidated the consequences of different DOPO dosages on the physical, rheological properties, and aging resistance of asphalt. The results of ¹H NMR and component analysis of asphalt disclosed that DOPO engaged in chemical reactions with the unsaturated groups within the asphalt, catalyzing a metamorphosis of saturates into aromatics and resins. Such chemical transformations were instrumental in augmenting the softening point, viscosity, and rutting propensity of the asphalt while imposing a minimal impact on its penetration and ductility. Post exposure to the thin film oven test (TFOT), pressure aging vessel (PAV), and ultraviolet (UV) aging, the DOPO modified asphalt (DMA) exhibited a diminution in the increment of softening point and viscosity aging index relative to the control asphalt. Furthermore, the DMA showcased enhanced retention rates of penetration and ductility, coupled with substantially reduced shifts in complex modulus and phase angle post-aging, underlining its superior aging resistance. Fourier transform infrared spectroscopy analysis revealed a comparatively slower rate of change in carbonyl and sulfoxide groups in DMA after aging, as opposed to the control asphalt. Notably, DMA exhibited enhanced resistance to UV aging relative to TFOT and PAV aging scenarios, a trait attributable to remarkable UV absorption capabilities of DOPO. Fundamentally, DOPO enhanced the high-temperature performance and aging resistance of asphalt while simultaneously diminishing the emission of noxious fumes.

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Steel slag-based geopolymer foamed concrete (SSGFC) provide a promising value-added and carbon-neutral strategy for the re-utilization of SS, and the strength and physical properties of SSGFC are essential to its practical application. Therefore, this study proposes to use emulsified asphalt (EA) to improve the pore structure, compressive strength, water resistance and thermal insulation properties SSGFC. Firstly, different contents of EA were added into the foaming solution to prepare modified foam, and then SSGFC samples were prepared by using modified foam and steel slag-based geopolymer. The fresh properties, microstructure, pore structure, reaction products and physical properties of SSGFC samples were investigated. The results indicate that EA can reduce the fluidity and settlement value of the paste and increase the setting time. The addition of EA leads to a decrease in hydration products, but it can reduce the average pore diameter of the SSGFC and improve its pore diameter distribution. The SSGFC sample prepared by modified foam with 10 % EA showed the best physical properties. Compared with the control group, its compressive strength increased by 21.4 %, water absorption decreased by 16.5 %, and thermal conductivity decreased by 31.3 %. Therefore, EA shows significant potential to enhance the performance of SSGFC, thus providing reliable support for its practical applications.

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An asphalt joint is formed when a fresh mix is laid and compacted next to an existing layer, brings about temperature difference during compaction, and therefore requires extra care in quality control and expose to higher cracking risks. Self-healing asphalt aims to stimulate the healing capacity of asphalt mixture and prolong its service life. The main objective of this study is to develop and optimize a calcium alginate capsules healing system for an asphalt joint mix. Capsules following two different self-healing concepts were prepared, namely conventional alginate capsules and conductive alginate capsules. Microscopy, Computed Tomography (CT) and Thermogravimetry analysis (TGA) were used to investigate the performance of alginate capsules. The results show that both types of capsules have a porous structure and a stable performance under high temperature, and therefore potentially survive from the asphalt mixing and production process. These capsules will be implemented and evaluated in full asphalt mix in future research.

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As the main waste product of iron and steel industry, steel slag possesses considerable cementitious activity, making it a promising alternative to cement in Cement Stabilized Macadam (CSM). However, CSM was inevitably exposed to groundwater and rainwater when served as the pavement base course, leading to concerns over poor early strength and potential pollutant leakage, which are the main factors that may hinder the widespread utilization of steel slag in CSM base. To address these issues, this study investigated the feasibility of using steel slag powder to produce CSM. Steel Slag Powder-Cement Stabilized Macadam (SSCSM) samples were prepared and the hydration products, microstructure, mechanical properties, water damage resistance and heavy metal ions leaching behavior were investigated. The results show that the nucleation effect of steel slag powder accelerates the early hydration, but the C-S-H produced by hydration is not sufficient to form a stable hydration product network, so the microstructure of SSCSM is looser than that of CSM. The addition of steel slag powder improved the shrinkage performance of SSCSM, and the mechanical properties and heavy metal ion leaching concentration of SSCSM meet the engineering application requirements when the steel slag powder replacement level does not exceed 30 %. It was also found that the addition of steel slag powder promoted the development of pores in SSCSM samples after dry-wet cycles, resulting in the reduction of water damage resistance. Compared with conventional CSM, the use of SSCSM can not only reduce 4 % of raw material cost and 23.5 % of equivalent CO₂ emission, but also mitigate the heavy metal ions leaching risk associated with steel slag, making it an effective and sustainable solution for steel slag recycling.

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Microwave heating is an effective method to achieve autonomic crack healing in asphalt mixtures, and the use of microwave-absorbing materials can largely improve this healing efficiency. As a solid waste, coal gangue contains metal oxides, which shows the possibility of microwave heating. In order to further promote the application of coal gangue in the microwave healing of asphalt mixtures, this study looks into the synergistic effect of basalt and coal gangue powder (CGP) on the microwave heating self-healing of an asphalt mixture. The mechanical performance, water stability, low-temperature crack resistance and microwave healing efficiency of the asphalt mixture were investigated using the immersion Marshall test, standard Marshall test, Cantabro test and semi-circular bending (SCB), and healing tests, respectively. The results indicated that the addition of CGP in asphalt mixture can improve the microwave heating speed, which also showed a significant advantage in water stability and fracture energy recovery. The research results will further promote the utilization rate of coal gangue.@en

Moisture erosion is one of the key factors leading to asphalt pavement damage, and the erosion depth indicates the moisture damage level but it is usually neglected. In order to study the moisture erosion and the erosion depth, this study characterized the chemical structure, rheological property and adhesion property of asphalt at different depths after immersion for different periods. To further explore the diffusion mechanism of eroded asphalt, a Log-log numerical model was established based on the Fick's second law to calculate the diffusion coefficient throughout the depth. The results indicate that it takes just four hours for water to penetrate a 25 μm asphalt film. The relation between erosion depth and immersion period presents three stages, and the process can be fitted with a polynomial model. At the macroscopic level, there is a lag between the changes in adhesion property with chemical structure and rheological property. Additionally, the periodicity of moisture erosion process was verified by the calculation of diffusion factor. In summary, the diffusion mechanism of eroded asphalt by moisture can provide a theoretical basis for the development of laboratory moisture erosion test specification, thus avoiding the waste of raw materials.

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Polymer Ca-alginate capsules with rejuvenator bring a high healing level for asphalt concrete under dry healing environments; however, the healing levels of bituminous mixtures containing capsules under water healing conditions are still unknown. In view of this, this study aimed at exploring the healing levels of asphalt concrete containing polymer capsules under various solution healing conditions following cyclic loads. This study involved the preparation of capsules, followed by the evaluation of their morphological characteristics, resilience to compression, thermal endurance, and rejuvenator content. The assessment of the healing properties of asphalt concrete utilizing capsules was conducted through a fracture–heal–refracture examination. This study conducted Fourier transform infrared spectrum experiments to determine the rejuvenator release ratio of capsules under dry conditions and the remaining rejuvenator content in extracted bituminous binder from capsule–asphalt concrete after solution treatment. Meanwhile, a dynamic shear rheometer was utilized to investigate the rheological characteristics of asphalt binder. Results revealed that the healing ratios of capsule–asphalt concrete beams under a dry healing environment were significantly higher than that of beams under various solution healing conditions, and the alkali solution has the worst effect on the improvement in healing ratio. The coupled impact of moisture intrusion and ion erosion resulted in an enhancement of complex modulus of asphalt binder while concurrently reducing its phase angle. Consequently, the restorative capacity of the asphalt binder was weakened.

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Aimed to address the low utilization rate of steel slag (SS) and its challenge in resource utilization in China, this study developed ternary geopolymers made by high-content (50%) SS together with fly ash (FA) and granulated blast furnace slag (GBFS). The effects of GBFS content (0–40%) and curing methods (water curing, standard curing, sealed curing, and heat curing) on the working performance and microstructure of geopolymers were investigated. Microscopic analysis such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM) were utilized to investigate the hydration process and products of geopolymers under different curing conditions and GBFS content. The results indicated that when the GBFS content increased from 0% to 40%, the fluidity of the mixture decreased by 11.7%, the initial setting time of the geopolymer slurry decreased by 76%, and the geopolymer mortar's 28d compressive strength increased from 31.9 MPa to 60.6 MPa. At room temperature, the geopolymer mortar's 28d compressive strength was higher under standard curing (70.8 MPa) compared to water curing (57.5 MPa) and sealed curing (68 MPa). The geopolymer mortar cured at 60 °C for 24 h exhibited the highest 28d compressive strength (76.3 MPa). However, excessively high curing temperatures or prolonged durations led to more shrinkage cracks and reduced the compressive strength. The microscopic analysis revealed that the main gel products of ternary geopolymer were C-(A)-S-H gel. The amount of gel products is directly related to the strength of geopolymers. The developed ternary geopolymer has the potential to promote the large-scale utilization of SS in the concrete industry, making a significant contribution to sustainable development.

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Asphalt fumes released during pavement construction posed a threat to human health and environment. In this study, 9,10-dihydro-9-oxa-10-phosphorophenanthrene-10-oxide (DOPO) was used as a reactive fumes suppressant to reduce the asphalt fumes emission. The volatilization behavior of DOPO modified asphalt (DOPO-Asphalt) was investigated through thermogravimetric analysis, volatility test and thermal destruction gas chromatography mass spectrometry, and effect of DOPO on the chemical structure and composition of asphalt was explored through nuclear magnetic resonance hydrogen spectroscopy, Fourier transform infrared spectroscopy, and asphalt component testing. The results indicated that 1.0 wt% DOPO reduced the fume content of control asphalt by 1.1% from 120 ℃ − 200 ℃ and the H₂S and VOC content by 96.9% and 84.2%, respectively, at 180 ℃. Moreover, 1.0 wt% DOPO reduced the content of aliphatic hydrocarbons, hydrocarbon derivatives, aromatics, and sulfides in control asphalt fumes by 86.8%, 89.7%, 90.7%, and 93.5%, respectively, which may be attributed to electrophilic and nucleophilic reactions between DOPO and volatile substances in asphalt. Chemical structure and composition changing of DOPO-Asphalt confirmed that P-H bond in DOPO was chemically reacted with components in asphalt, generating stable aromatic hydrocarbons and resins. The results provided a novel method for inhibiting the volatilization of harmful substances in asphalt.

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Self-healing is a biological phenomenon in which living organism responds to the suffered damage in a complex way. Inspired by the self-healing phenomenon in nature, various biomimetic healing methods rooted in intrinsic or extrinsic healing mechanisms have been explored. Research on novel self-healing asphalt materials with intelligent response is at the cutting-edge of materials science and offers a potential strategy for building long-life and low-carbon asphalt concrete infrastructure. This paper describes the progress of research on extrinsic self-healing asphalt materials and makes a clear distinction between intrinsic and extrinsic self-healing. The asphalt self-healing mechanism is interpreted by capillary flow theory, phase field theory, molecular diffusion theory and surface energy theory form various perspective. The extrinsic self-healing strategies including thermal induced healing and rejuvenator induced healing are proposed to enhance the healing level of cracked asphalt materials. A brief review of the methods including fracture-healing test and fatigue-healing test for assessing the efficacy of different extrinsic healing methods is presented. The thermal induced healing method bring high crack repair efficiency for asphalt concrete and the rejuvenator induced healing strategy not only improve the healing ratio of cracked asphalt concrete but also regenerate the ageing asphalt in situ. Important lessons for prospective research on the creation of novel self-healing asphalt materials are highlighted.

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Layered double hydroxides (LDHs) can shield polymeric materials from UV light, which allows reducing material aging and erosion damage of bituminous pavement under physical and chemical action. In this study, the physicochemical properties, aging resistance, and erosion resistance to the aqueous solution of LDHs modified bitumen mastic (BM) were characterized by Fourier-transform infrared spectroscopy, basic physical tests, viscosity tests, a dynamic shear rheometer, and a bending beam rheometer. The results show that few chemical reactions occurred between LDHs and BM, indicating that a physical mechanism underlay the modification of BM by LDHs. Moreover, LDHs could increase the flow activation energy of BM by 0.12%, increase the high failure temperature from 69.07 °C to 71.07 °C, and decrease the low failure temperature from −10.50 °C to −12.39 °C. Therefore, LDHs could slightly reduce the temperature sensitivity of BM, while slightly enhancing the high and low-temperature rheological properties of BM. Compared with short-term aging and long-term aging, LDHs could significantly improve the UV aging resistance of BM. The above results are consistent with previous studies of LDHs-modified bitumen. Furthermore, water and pH 3 acidic solutions had the greatest degree of erosion to BM, and LDHs could improve the resistance to aqueous solutions. Overall, this study can help to investigate the effects of various environmental factors on the performance of LDHs modified bitumen pavements during long-term use.@en

Using solid waste to replace limestone filler in asphalt concrete can not only reduce the cost of road construction, but also improve the utilization rate of solid waste. In this study, PHC pile waste concrete (PPWC) was innovatively used to replace limestone filler in asphalt mixture and its effect on the physical and rheological properties of asphalt mastics was studied. Firstly, PPWC was ground into filler particles with a diameter less than 0.075 mm. The physical properties, particle characteristics and chemical composition of PPWC filler and limestone filler were compared. Asphalt mastics were prepared with different filler-asphalt volume ratios (20%, 30% and 40%) and the physical properties, high-temperature rheological properties and low-temperature cracking resistance of asphalt mastics were tested. The experimental results showed that the surface of PPWC filler is rougher and has lower density and smaller particle size than limestone filler. When the filler content is the same, PPWC filler asphalt mastics have lower penetration and ductility, higher softening point than limestone filler asphalt mastics, and the viscosity of PPWC filler asphalt mastics is more sensitive than limestone filler asphalt mastics. PPWC filler asphalt mastics demonstrated superior high-temperature stability, but poorer low-temperature cracking resistance compared to limestone filler asphalt mastics. In conclusion, PPWC fillers can be used to replace limestone fillers in asphalt mixtures. The finding of this study will provide a new solution for the construction of eco-friendly roads.

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As a kind of solid waste, using Prestressed High-Strength Concrete Pile Waste Concrete (PPWC) as the replacement for limestone filler in asphalt concrete can not only reduce the accumulation of PPWC and increase its utilization but also avoid the increased road construction costs and environmental degradation associated with limestone mining. This study aims to investigate the effect of using PPWC filler to replace limestone filler on the road performance of asphalt concrete. Firstly, PPWC was ground into filler particles with a diameter less than 0.075 mm. The particle characteristics such as surface morphology, particle size distribution and chemical composition of PPWC filler and limestone filler were compared. Then, PPWC filler was used to replace limestone filler with different volume fractions to prepare asphalt concrete, and the water damage resistance, high-temperature rutting resistance, low-temperature crack resistance, fatigue resistance and adhesion performance of asphalt concrete were tested. The results showed that PPWC filler has a smaller particle size and rougher surface than limestone filler, and it contains Ca(OH)₂ produced by hydration. The addition of PPWC filler can effectively improve the mechanical properties of asphalt concrete without reducing its water damage resistance. PPWC filler can improve the high-temperature rutting resistance and low-temperature crack resistance of asphalt concrete, but reduce its low-temperature fatigue resistance. The low content of PPWC filler will enhance the adhesion between asphalt mortar and aggregate. However, when the content of PPWC filler exceeds 50%, Ca (OH)₂ in PPWC will reduce the adhesion between acid asphalt mortar and alkaline basalt aggregate. Therefore, the use of PPWC as filler in asphalt mixtures provides a reliable solution for the sustainable development of road materials.

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This research aimed to explore the impact of aging on the molecular structure of asphalts from different crude oils. The elemental composition of five types of original asphalts was measured. The structure changes of the asphalts were analyzed with Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR) before and after thin-film oven test, ultraviolet light (UV), and pressure aging vessel (PAV). The result of the elemental analysis showed that the hydrogen-carbon ratio (H/C) of asphalts ranges from 1.347 to 1.602 with different contents of sulfur, nitrogen, and oxygen. The FTIR indicated that asphalts with a low H/C had a low rate of change of carbonyl index after aging. Asphalts were more likely to produce an aromatic ring structure and sulfoxide group during the PAV aging process. The aliphatic structure was easier to reduce during the UV aging process. The 1H-NMR analysis showed that the content of aromatic hydrogen (Har) of asphalts is between 0.022 and 0.056, the content of Har decreased after aging, and the asphalt with a low Har content had a smaller change rate of hydrogen atom content. The outlined research results revealed that the asphalt with lower H/C and Har content was prone to have better aging resistance.@en

During the service period, asphalt materials are affected by various natural factors, including heat, ultraviolet light, oxygen and moisture, etc., resulting in the reduction of pavement performance, the increase of pavement distress and shortening of service life. This study aims to investigate the aging performance of asphalt under multiple aging conditions of heat, UV and aqueous solution. Thermal-oxygen aging, UV aging and hydrostatic erosion tests were carried out sequentially on asphalt. The rheological properties, chemical structure and element composition of asphalt were characterized before and after aging, and the effect mechanism of multiple conditions was discussed. The results show that the multiple conditions of heat and UV can increase the rutting resistance and weaken the cracking resistance of asphalt. However, the effect degree of UV decreases gradually with the deepening of aging degree. Additionally, the effect of water on the physicochemical properties is less than that of UV; however, water can increase the sensitivity of physicochemical properties to UV. In summary, this study explored the short-term cycling effect of heat, light and water on asphalt and provided an idea for simulation test of asphalt under multiple aging condition.

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Self-healing technology, such as encapsulated rejuvenator, induction heating or combination of the above two methods, has been demonstrated to be a promising autonomic crack healing mechanism for porous asphalt. With the advantage of low cost, environmentally friendly and excellent performance, the calcium alginate capsules encapsulating rejuvenator showed promising effect to promote the crack healing in asphalt concrete. However, the healing effect of the calcium alginate capsules on the damage from fatigue loadings is still unknown, therefore became the research focus of this study. To this aim, the calcium alginate capsules were produced and incorporated into the porous asphalt (PA). A laboratory ageing process was performed on the PA to simulate the situation when asphalt pavement prone to cracking and a healing needs to take place. Afterwards, the four-point bending fatigue test (4PBF) was employed to characterize the fatigue resistance of the PA specimens. A 24-hour-rest period was carried out to allow the healing of fatigue damages. Additionally, a 4PBF testing and healing programme was carried out to evaluate the fatigue damage healing efficiency of the calcium alginate capsules healing system. It was found that the capsule healing mix showed a higher fatigue life than the reference mix, but the results were a bit scattered which might be caused by the capsule distribution which determines whether the healing takes place on the damage site or not.

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