Water and Chloride Ion Transport Characteristics of Unsaturated Aeolian Sand Mortar under Capillary Absorption

Abstract

In this study, we investigate the water and chloride ion (Cl−) transport properties of aeolian sand mortar (ASM) in an unsaturated state. Capillary absorption tests were conducted on ASM with varying water-to-binder ratios and different concentrations of chloride salts in clear water solutions. The Cl− content at different depths in ASM was determined using layered drilling, powder extraction, and chemical titration. The relationship between water and Cl− transport properties under capillary absorption was examined. The results indicate that moisture serves as a transport medium for Cl− in mortar, but its transport depth is significantly smaller than that of water, revealing a non-synchronization between the two transports. The transmission depth and capillary absorption ratio of water in the mortar decrease with increasing initial saturation. A linear relationship between water and Cl− transport depths is observed within the first 7 days of capillary absorption. Beyond 7 days, the water transport rate gradually slows down, while Cl− continues to be transported due to the presence of an ion concentration gradient. As the initial saturation increases, the percentage of gel pores decreases, and the percentage of transition pores and capillary pores in the matrix increases. Finally, incorporating the theory of unsaturated capillary water absorption, we introduce Boltzmann variables and develop a predictive model for the relative water content distribution under capillary water absorption in ASM. This study provides a theoretical foundation for the widespread application of ASM, and the proposed research model offers new insights into the underground environment and the durability of concrete structures affected by moisture transport.