Laboratory Investigation on Physical, Rheological Thermal and Microscopic Characteristics of Water-Foamed Asphalt under Three Environmental Conditions

摘要

Applications of water-foamed binders have received widespread attention due to its environmental and economic benefits. This study aims to evaluate the properties of water-foamed asphalt under three environmental conditions (high-temperature evaporation, low-temperature frozen and the freeze–thaw cycle). Conventional physical properties tests, dynamic shear rheometer test (DSR), differential scanning calorimetry test (DSC) and scanning electron microscope test (SEM) are employed to assess the physical, rheological thermal and microscopic characteristics of samples. Conventional physical properties test results showed that the performance of a foamed binder had declined under three environmental processes and the foamed asphalt gradually returned to the characteristics before being foamed, with the increase of process time. A comprehensive evaluation index, deterioration degree was proposed based on the test results and entropy theory, and the deterioration process of the foamed binder under three environmental conditions was quantified. Moreover, freeze–thaw (F–T) cycles had been proved to have the most significant influence on the performance of a foamed binder among three environmental factors, which was a key issue that limits the application and promotion of foamed asphalt in seasonal frozen regions. The DSR test showed that the resistance to high-temperature permanent deformation of the foamed binder was improved after F–T cycles, and the fatigue resistance became worse. The sensitivity analysis of complex modulus and frequency illustrated that foamed asphalt after F–T cycles were more sensitive to the loading frequency and less sensitive to the temperature. The DSC test indicated that the thermal stability of foamed asphalt was improved after F–T cycles. The disappearance of circular “cavitation” observed through SEM test revealed that moisture of foamed asphalt was gradually precipitated and self-healing phenomenon occurred during F–T cycles.