Influence of chlorides and salt concentration on salt crystallization damage of cement-based materials

Abstract

Durability of concrete exposed to physical salt attack (PSA) has primarily been studied on specimens partially submerged in sulfate solution. However, in sulfate-containing soils, chlorides are often present. The aim of this study is to investigate the influence of salt concentration and the presence of chlorides on the deterioration of cement-based materials caused by PSA. Cement mortars partially submerged in three different concentrations of sodium sulfate solutions (5%, 9% and 13%) and two mixed Na2SO4–NaCl solutions (5%–2% and 5%–5%) and exposed to cyclic drying-wetting were investigated. The crystallization behavior of salt solutions and the alteration in the macroscopic properties and microstructure of the specimens were observed to understand the differences in deterioration. The results showed that the presence of chloride ions significantly reduced the surface scaling above the solution level. Microstructural characterization suggested that thenardite tended to precipitate homogeneously in the specimens partially submerged in solutions containing chlorides. Consequently, crystallization pressure is less likely to develop in such a case. On the contrary, for the specimens partially submerged in pure sodium sulfate solutions, a higher concentration of salt solution facilitated more thenardite accumulation in a thin layer beneath the surfaces, which in turn accelerated the damage process. The findings may improve guidance on the evaluation of concrete resistance to PSA when chlorides are detected in sulfate-bearing environments.