Long-term behaviors of concrete under low-concentration sulfate attack subjected to natural variation of environmental climate conditions

Abstract

Accelerated laboratory tests on resistance of concrete exposed to sulfate attack have generally been conducted in high-concentration sulfate solutions or under drastic drying-wetting cycle conditions. However, these accelerated regimes radically alter the nature of sulfate attack mechanisms on concrete under real field exposure situation. To obtain reliable information on the long-term behaviors of concrete under real field conditions, the behaviors of concrete samples under three different exposure regimes, i.e., continuous full immersion, full immersion with general use drying-wetting cycles and full immersion with natural drying-wetting cycles, were investigated in this research. Three different concentrations of sulfate sodium solutions, i.e., 0% water for control, 2.1% for field-like condition and 15% for high-concentration condition, were considered. Physical and mechanical properties, such as mass, expansion, permeability and compressive strength, were tested at regular time intervals during the whole exposure period to describe the associated evolution laws. Microanalysis was also carried out to identify the underlying mechanisms. Results from this study showed that the exposure regime of full immersion in 2.1% sulfate sodium solutions subjected to natural drying-wetting cycles can well reproduce the field exposure condition of concrete under certain sulfate-rich environments. Both concentration and exposure type affect the nature of sulfate attack mechanism on concrete, along with the evolution of physical and mechanical properties. A three-stage evolution model, consisting of the enhancement stage, the incubation stage and the degeneration stage, was observed in the property evolution of concrete samples under the field-like exposure condition. Meanwhile, a distinct coupling physicochemical damage on concrete samples was detected when subjected to drying-wetting cycle exposure. In addition, the effects of water-to-binder ratio and binder type were duly studied.