Mesoscale study of water transport in mortar influenced by sodium chloride

Abstract

Transport properties of mortar exposed to salt solution are fundamental information for understanding the durability of mortar. In this paper, change in moisture uptake behaviors due to sodium chloride (NaCl) contamination was studied. To understand the salt contamination effect, mortar samples with different water-to-cement ratios (w/c) in meso scale were immersed into deionized (DI) water, intermediate (3%wt), and high (20%wt) concentration of NaCl solutions for three days. After immersion, the re-dried samples were sequentially immersed in DI water at room temperature for seven days. Based on the test results, two-stage solution diffusion model was developed, which can describe the solution absorption process efficiently. The salt contamination may be due to calcium (Ca²⁺) leaching and salt crystallization. As found, when exposed to low concentration NaCl solution, the diffusivity of mortar would increase due to faster Ca²⁺ leaching. However, for high concentration NaCl solution, it would be reduced since pores filled by crystallized salt have dominant effect in this case. The salt crystallization mainly occurs at small pores because there is little difference at initial absorption but the difference becomes significant for long time absorption.