Investigation of binary blended cement mortar degradation driven by sulfate attack and thermal gradients in arid environments

Concrete structures in hot climates are subject to accelerated deterioration due to the combined influence of elevated temperatures, moisture fluctuations, and aggressive chemical exposure. This study examines the effects of thermal diffusion and related environmental stressors on the progression of sulfate attack in mortar. Mortar beams and cubes were prepared using ordinary Portland cement as well as blends incorporating silica fume and ground granulated blast furnace slag. These samples were exposed to 10% w/v Na ₂ SO ₄ and MgSO ₄ , solutions for up to 120 days. Mortar samples were subjected to sulfate attack under varying thermal and moisture regimes, including isothermal immersion and partial exposure at 50°C. Results show that exposure to MgSO ₄ led to significant mass and volumetric increases due to salt crystallization within pores and on surfaces, whereas samples exposed to thermal gradients experienced the greatest mass and volume losses, attributed to drying shrinkage and thermal stress. Flexural strength was reduced under thermal diffusion compared to isothermal conditions, highlighting the accelerating effect of thermal and humidity gradients on mechanical degradation. Notably, mortars incorporating both SF and GGBFS exhibited a 10–13-fold increase in electrical resistivity pre-exposure and 7–10-fold post-exposure relative to ordinary mortars, highlighting their efficiency in mitigating chemical ingress. Ultrasonic pulse velocity (UPV) decreased by up to 8% under thermal diffusion, while samples under isothermal exposure showed improved UPV, reflecting continued hydration and pore filling by expansive products. These findings emphasize the role of binder composition and the influence of thermal diffusion on concrete degradation in aggressive environments.