Measurement and optimization of estimation method for moisture diffusivity of porous building materials with different salt content

Abstract

Sintered bricks, common porous building materials in architectural heritage, necessitates an accurate understanding of moisture diffusivity for effective moisture transfer analysis. Using the “ruler method” proposed by Evangelides et al., based on pure water capillary absorption experiments, we determined the moisture diffusivity (D_l) of Chinese sintered blue brick containing sodium chloride (NaCl) crystals. Before the experiments, the samples were immersed in 0%, 1%, 5%, and 10% NaCl solutions and dried to contain salt crystals. Subsequently, based on the D_l values measured by the ruler method, a heat and moisture coupled transfer model was developed to discuss the applicability of the moisture diffusivity obtained from the ruler method by reproducing the pure water capillary absorption process of sintered bricks with different salt contents. Experimental results showed that the capillary absorption coefficient (A_cap) and capillary moisture content (w_cap) of sintered bricks both decreased with increasing NaCl content, with maximum reductions of 18% and 8.6%, respectively. The D_l increased with elevated salt content in lower moisture content range but decreased in higher moisture content range. The simulation results indicated that the choice of boundary moisture content played an important role in the determination of moisture diffusivity in porous building materials and using saturated moisture content (θ_sat) over capillary moisture content (θ_cap) can give more suitable moisture diffusivity and the moisture content above θ_cap cannot be ignored in the ruler method. This research not only extends the ruler method’s applicability for sintered bricks but also provides support data for moisture simulations and conservation initiatives related to sintered brick architectural heritage.