Effects of incorporating polynary SCMs on sulfate resistance and chloride impermeability of concrete considering capillary action in dry-wet cycling environment

The incorporation of supplementary cementitious materials (SCMs) in concrete can improve the properties of concrete partially immersed in salt solution. However, the current partial immersion environment only considers the capillary action above the still water level, does not consider the capillary action above the fluctuating water level in dry-wet cycling environment. In this paper, a series of indoor exposure experiments were carried out to investigate the effects of incorporating polynary SCMs including fly ash (FA), ground granulated blast furnace slag (GGBFS) and silica fume (SF) on the sulfate resistance and chloride impermeability of concrete considering the capillary action above the fluctuating water level in dry-wet cycling environment. A total of 15 groups of concrete with different mix proportions (total 150 concrete specimens) were designed to study the effects of different replacement levels of polynary SCMs on concrete properties. The effects of incorporating polynary SCMs on the chloride impermeability of concrete above and in the fluctuating water level zone were investigated. The scanning electron microscope (SEM), x-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were used to analyze the microstructure of concrete. The results indicate that when concrete is incorporated with polynary SCMs and subjected to capillary action above the fluctuating water level, the compressive strength and chloride impermeability first increase and then decrease with the increase of FA content; the compressive strength and chloride impermeability decrease with the increase of GGBFS content; the compressive strength first increase and then decrease with the increase of SF content, and the chloride impermeability increase with that. The transport process of chloride in concrete above the fluctuating water level zone includes the longitudinal transport under capillary action and the transverse transport under concentration gradient action. The combined effects of both cause the higher chloride concentration in concrete above the fluctuating water level zone. Comprehensively considering the influence of different mix proportions on the sulfate resistance and chloride impermeability of concrete, it is determined that 20% FA + 5% SF is the optimal replacement level with the excellent performance considering the capillary action above the fluctuating water level in dry-wet cycling environment.