Self-healing capability of asphalt mixture containing polymeric composite fibers under acid and saline-alkali water solutions

Self-healing capability of the asphalt mixtures containing encapsulated healing agent can be affected by different water components as results of their exposure to aggressive environmental conditions such as the acid rain or saline-alkali solutions in coastal areas. In view of this, this paper aims to study the effect of harmful water environments on the self-healing capability of asphalt mixtures containing a kind of novel composite fibers. The Ca-alginate/SiO₂ composite fibers encapsulating healing agent was synthesized by using a microfluidic device. Several tests were conducted to characterize the micromorphology, thermal stability and mechanical properties of the fibers. Effectiveness of the composite fibers in asphalt was observed by fluorescence microscopy. Additionally, three-point bending test was performed to measure the effects of different water environments (including acid, alkali and salt-water solutions) on the self-healing properties of asphalt mixtures with, and without fibers. Furthermore, the mechanism of the effect of different water environments on the self-healing performance of the asphalt mixture was studied by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis. Main results showed that the composite fiber encapsulated 61.9 wt% of healing agent, and the fibers could meet the temperature and mechanical requirements during the manufacturing process of asphalt mixture. The composite fiber worked and enhanced self-healing capability of asphalt. Harmful water environments did not weaken the effect of the composite fiber. Compared with the drying condition, the self-healing property of asphalt mixtures containing the composite fibers was further improved after being immersed in alkali and salt-water environment. The results indicated that the sodium ions in the alkaline solution and the salt solution could undergo a de-crosslinking chemical reaction with calcium alginate in the fiber wall, as a result of which more healing agent leaked out to soften and rejuvenate asphalt. In short, the composite fibers encapsulating healing agent worked, and these were successfully applicable into asphalt mixture under different water environments.