Evolution of moisture transport properties in cement mortar under marine salt spray environment

Chronic marine salt spray exposure critically alters pore structure and hygrothermal performance ofhistoric building materials. This study investigates the humidity-dependent water vapor permeability (δv) of cement mortar with salt deposition. Using accelerated salt spray testing (35 cycles) and cup tests across humidity gradients, cement mortar exhibited opposing δv responses: a reduction of 1.86 × 10–12 kg/(m s Pa) under low humidity from pore blockage, and an increase of 1.98 × 10–11 kg/(m s Pa) at high humidity from brine migration. A predictive piecewise model (R² > 0.95) incorporating salt content and ambient humidity thresholds was developed. MIP and SEM analyses revealed NaCl crystallization preferentially occupying 0.02–0.12 μm pores within the top 2 mm, reducing porosity by 42% while creating dual transport modes: pore occlusion (dry) and interconnected brine networks (humid). These findings provide a framework for predicting moisture dynamics in porous materials under salt spray climates, enabling improved hygrothermal simulations for coastal historic buildings.