Impact of reused tire rubber waste on liquid-phase moisture transfer properties of cement mortar

This study investigates the influence of waste tire rubber (WTR) on the liquid-phase moisture transport properties in cement mortar under ambient conditions—an area that is still insufficiently explored in current literature. While most studies have focused on mechanical performance, this work integrates capillary absorption testing with a liquid-phase moisture transfer model calibrated using experimental data to quantify sorptivity and water diffusivity. Seven mortar mixtures were prepared: one control (no WTR), three with WTR powder replacing 7%, 14%, and 21% of sand by volume, and three with rubber aggregates at the same replacement levels. The study systematically compares the effects of WTR in both powder and aggregate forms on key parameters such as sorptivity, water diffusivity, accessible porosity, and compressive strength. Capillary absorption tests provided empirical data for model calibration and analysis of liquid-phase moisture transfer behavior. Results showed that WTR substitutions up to 14% reduced accessible porosity by 18.03% and sorptivity by up to 351%, attributed to the hydrophobic nature of rubber, which impedes capillary flow. However, at a 21% replacement level, both porosity and sorptivity increased, while compressive strength declined—indicating that high WTR content compromises mechanical integrity and limits suitability for structural use. Water diffusivity exhibited two regimes: a low-diffusivity phase (<0.01 mm 2 /s) under partial saturation, and a higher-diffusivity phase at near-saturation, consistent with dual-regime moisture transfer models. WTR incorporation led to more tortuous pore structures, which reduced water ingress and improved moisture resistance. WTR powder was more effective than rubber aggregates in reducing sorptivity and porosity, particularly at replacement levels up to 14%. WTR powder at replacement levels up to 14% improved moisture resistance, suggesting its potential use in non-structural cement elements such as renders and plaster coatings. The results clarify how WTR particle morphology influences pores connectivity and liquid-phase moisture transfer, supporting its potential for enhancing durability in moisture-sensitive, non-load-bearing cement applications.