The Moisture Transport Properties of Cement Mortar under Salt Spray Deposition

The moisture transport properties of porous materials play a crucial role in building energy consumption and indoor thermal comfort. Due to the salt spray climate, the external boundary conditions of buildings in coastal areas differ significantly from those in inland regions. Under salt spray deposition, salt crystals accumulate and expand within the pores of building materials, which not only causes severe erosion and weathering of the envelope but also alters its moisture transport properties. Previous studies have focused extensively on the physical- mechanical properties and durability of salt-laden building materials, while the moisture transport properties and mechanisms of building materials under salt spray deposition remain unclear. To address this issue, this thesis conducted the following work: 1）Development of an accelerated salt spray test method for porous building materials. Based on international standards and relevant literature, the main control parameters and technical indicators of accelerated salt spray tests were analyzed and discussed. Combined with the core objectives and technical requirements of this study, an accelerated salt spray test method was established, particularly tailored to investigating the hygric properties of porous building materials. 2）Ion migration and crystal distribution of sodium chloride in cement mortar. The salt crystal distribution and chloride migration patterns of cement mortars with different water-cement ratios and surface evaporation conditions were determined after 120 days of semi-immersion in a 5 wt% NaCl solution. Both the clogging of internal pores by salt crystals and the sealing of external surfaces with resin significantly affect the capillarity and moisture transport properties of cement mortar. 3) Liquid transport properties of cement mortar under salt spray deposition. Vacuum saturation tests and capillary absorption tests were performed on specimens subjected to 0–35 salt spray cycles using modified methodologies. Salt spray deposits in the specimens were observed to increase apparent density while decreasing open porosity and saturated moisture content. Based on fitting formulas for salt influence factors, correction equations for the capillary absorption coefficient and capillary moisture content of cement mortar under salt spray deposition were established. 4) Vapor transport properties of cement mortar under salt spray deposition. Sorption isotherms and vapor permeability of specimens with varying salt spray deposition were measured and analyzed using standardized protocols. By correcting the equilibrium moisture content of specimens above the deliquescent humidity of NaCl via the Robinson-Stokes equation and Nielsen formula, segmented fitting equations for the equilibrium moisture content of cement mortar under salt spray deposition were derived. Additionally, correction equations for the water vapor permeability of cement mortar under salt spray deposition were established based on segmented adjustment formulas for salt influence factors. From the perspective of moisture transport in porous building materials under coastal salt spray climates, this study investigated the influence mechanisms of salt spray deposition on the transport and storage properties of liquid water and vapor, using cement mortar—a commonly used porous construction material—as the test medium. Revised calculation equations were developed for several key hygric property parameters of cement mortar under salt spray deposition. This research lays a foundation for the accurate calculation of moisture-heat loads and energy consumption in coastal buildings.