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

In hot climates, concrete deteriorates faster due to high temperatures, moisture changes, and chemical attack. This study examines the effects of thermal diffusion and related environmental stressors on the progression of sulfate attack in mortar. Prismatic mortar specimen and cubes were fabricated 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 Na₂SO₄ and MgSO₄, solutions for up to 120 days. Mortar samples were subjected to sulfate attack under varying thermal and moisture regimes, including isothermal immersion and partial immersion at 50 °C. Results show that exposure to MgSO₄ 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 declined under thermal diffusion, showing accelerated degradation from thermal and humidity gradients. Notably, mortars with SF-GGBFS blends showed 10-13 times higher pre-exposure and 7-10 times higher post-exposure resistivity than ordinary mortars, demonstrating superior resistance to chemical ingress. Ultrasonic pulse velocity dropped up to 8% under thermal diffusion, whereas isothermal samples showed gains, indicating ongoing hydration and pore filling. These findings emphasize the role of binder composition and the influence of thermal diffusion on concrete degradation in aggressive environments.