The rapid development of economy has led to an increase of acid rain that can react with the bitumen physically and chemically, causing further damage to the bitumen properties. Therefore, the effects of acid rain on the chemical composition and rheological properties of bitumen at different depths were investigated in this study. Fourier transform infrared spectroscopy and dynamic shear rheometer tests were performed on the bitumen samples after immersion in acid rain. The results show that in the early stage of immersion, acid rain leads to carbonyl dissolution, reduction of complex modulus, increase of phase angle, and softening of bitumen, thus improving the fatigue cracking resistance. In the late stage of immersion, bitumen is gradually oxidized to form carbonyl group. The change degree of complex modulus and phase angle decreases, and the fatigue cracking resistance is weakened with time. The effect of acid rain on the fatigue cracking resistance fluctuates more for bitumen at 0~50 μm and is more stable for bitumen at 50~100 μm.

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.

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.

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.

In this paper, a method to predict the healing effect of induction heating asphalt concrete at vertical depths was proposed and verified. At first, AH-70 asphalt concrete and SBS modified asphalt concrete of AC-13 gradation were designed and prepared. R-DT (Relationship of Depth and Temperature) was quantified through induction heating test. R-HT (Relationship of Healing rate and Temperature) was quantified through fracture-healing–fracture test and X-ray micro computed tomography test with oven heating. Then, linear regression was used to verify the rationality of R-HT compared with the pre-relationship in previous studies. Finally, R-DH (Relationship of Depth and Healing rate) was predicted by fitting approach. It was found that R-DT and R-HT presented significant linearity, the existence of which was independent from the type of asphalt materials. While, more sensitive of SBS modified asphalt concrete showed that the response to gradient characteristics of R-DT was related to the higher overall temperature. Additionally, R Square-values = 0.963 of linear regression proved the oven heating method was suitable for the quantification and prediction of gradient characteristics. Furthermore, the prediction of R-DH was obtained successfully, which established the continuous distribution of the healing effect at vertical depths and revealed the linear relationship of the continuous distribution.

Aqueous solution is one of the main factors of asphalt pavement disease. However, the physicochemical changes of asphalt are ambiguous during immersion in different aqueous solutions. This study evaluated the physicochemical properties of asphalt under the action of different aqueous solutions to further understand the mechanism of moisture erosion. The morphology, chemical structure and four components of asphalt were observed after immersion, while the pH value, total organic carbon (TOC) and characteristic functional groups of residual solutions were monitored. The test results showed that aqueous solution could change the bee structure on the asphalt surface and increased the mean roughness. The carbonyl index (I_C=O) and sulfoxide index (I_S=O) of asphalt increased with immersion time. And the asphaltenes of asphalt fluctuated and eventually increased during immersion. Solute could accelerate the erosion on asphalt through interaction, the degree of which increased in the order, Na₂SO₄ saline < NaCl saline < pH 3 acid < pH 11 alkali.