A time-variant model of chloride diffusion in prestressed concrete cylinder pipe (PCCP) considering the effects of curing age

Abstract

Chloride penetration is considered as the most responsibility to steel corrosion for PCCP during service. Compared with ordinary concrete structures, the curing method of PCCP is generally steam-curing. Despite numerous contributions have shown that curing age has significant effect on the resistance to chloride penetration of concrete. There is still a lack of critical understanding of the curing age effect on the chloride migration in steam-cured concrete. For this reason, this paper aims to establish a chloride diffusion model suitable for PCCP. In this study, the non-steady-state chloride diffusion coefficient and chloride concentration of steam-cured concrete are measured through RCM test and chloride diffusion simulated test, respectively. The apparent chloride diffusion coefficient and surface chloride concentration are calculated based on Fick’s second law. Moreover, the instantaneous chloride diffusion coefficient was estimated. It is found that the steam-cured concrete cannot ignore the influence of curing age on the chloride penetration resistance, according to RCM test results, the non-steady-state chloride diffusion coefficient of 28 days decreased by 33 % compared with that of 3 days, while the chloride diffusion coefficient of 90 days decreased by 15 % compared with 28 days under steam curing. The larger the curing age, the smaller the chloride concentration at each depth, as well as the chloride diffusion coefficient and surface chloride concentration. In addition, it can be concluded that with the increase of exposure time, the chloride diffusion coefficient decreases gradually, while the surface chloride concentration increases gradually. Thus, the two kinds of test results and theoretical analysis were combined to establish the time-variant models of instantaneous chloride diffusion coefficient and surface chloride concentration of steam-cured concrete considering the effects of curing age and exposure time. On this basis, a new chloride diffusion model considering the effects of curing age, exposure time, the time-variant chloride diffusion coefficient and time dependence surface chloride concentration was established, which plays an important role in durability evaluation of PCCP.