Laboratory investigation on rejuvenating and self-healing properties of aged asphalt containing Ca-alginate capsules

Abstract

The aging and cracking of asphalt pavement seriously affect the service life of asphalt pavement. Calcium alginate capsules have been shown to release a rejuvenator to repair cracks inside asphalt concrete under traffic loading conditions. Previous studies have primarily focused on Ca-alginate capsule design and its influence on asphalt mixtures’ early performance. However, rejuvenating and self-healing of asphalt concrete by capsules mainly occur after asphalt aging, the performances during this period have rarely been investigated. Thus, the objectives of the research were to assess the effect of capsules on the mechanical properties and the self-healing ability of laboratory-accelerated aged asphalt mixture and asphalt mixture containing RAP and investigate the improvement mechanism of Ca-alginate capsules. In this dissertation, the volume performances, rutting resistance, moisture stability, crack resistance and self-healing performance of different prepared asphalt mixtures were measured by standard tests. The aged bitumen and extracted RAP binder with and without capsules were used to investigate the mechanism of rejuvenating and self-healing by diffusion, DSR, BBR and chemical component tests. The Ca-alginate capsules and laboratory aging had minimal impact on the volumetric properties of asphalt mixtures. The capsules reduce water stability and resistance to permanent deformation of asphalt mixtures, primarily due to the capsules’ substantial release of oil, which softens bitumen during incidents of rutting. Additionally, the crack resistance of asphalt mixtures at low temperatures was enhanced by the addition of capsules. After aging, the resistance to permanent deformation increased, while water stability and low-temperature crack resistance declined in all asphalt concrete samples. In cases where aged asphalt mixtures contained capsules, the anti-rutting performance decreased to the level of normal virgin asphalt mixtures; consequently, both water stability and low-temperature crack resistance were reduced. The presence of a small quantity (0.5wt%) of capsules was likely responsible for the observed effects. The Ca-capsules can effectively improve the strength healing rate and fracture energy healing rate of asphalt mixtures before and after ageing, which is mainly caused by the diffusion of the capsules’ oil into the asphalt which softens it. The self-healing rates of the aged asphalt mixtures containing capsules can also reach the level of ordinary virgin asphalt concrete without capsules. After applying Ca-alginate capsules and RAP (40%-70%) to asphalt mixtures, no effect on the asphalt mixtures’ volume performance was found. Replacement of RAP and Ca-capsules decreased the Marshall stability and residual Marshall stability of asphalt mixtures, and its negative effect became more pronounced as the amount of replacement of RAP increased. Moreover, Marshall stability has become the most important mechanical index of RAP replacement quantity in asphalt mixtures containing Ca-alginate capsules. Indeed, the presence of capsules decreases the rutting resistance and increases the crack resistance of asphalt mixtures, while RAP has the opposite effect. The comprehensive utilization of RAP and capsules can effectively prevent their respective shortcomings; in addition, a combination may be found that produces the same performance as that of the reference samples. The self-healing ability of asphalt mixtures containing RAP is lower than that of the virgin samples, while Ca-alginate capsules have significantly improved mixtures’ self-healing ability. The comprehensive utilization of capsules and RAP can therefore better make the asphalt mixtures containing RAP maintain their excellent self-healing ability for a long time, ultimately compensating for the shortcomings of using RAP. The bitumen tests showed that the reaction between the sunflower oil in the capsules and aged bitumen replenish the saturates and aromatics components, which can perfectly explain the improved performance of aged asphalt mixture. Additionally, based on DSR results, it can be demonstrated that the rheological properties and flow behavior index of aged bitumen that has been rejuvenated by the capsules can be restored to the level of virgin asphalt. This achievement serves the purpose of rejuvenating aged asphalt concrete and enhancing its self-healing capabilities. This thesis reveals in detail the influence of Ca-alginate capsules on the mechanical and self-healing properties of aged asphalt mixture and RAP asphalt mixture. It provides effective guidance and reference for the full-cycle application of Ca-alginate capsules in asphalt concrete pavement to effectively extend the life of asphalt pavement.