Durability Index and Microstructure Evolution of Magnesium Sulfate-Exposed One-Part and Two-Part Alkali-Activated Slag Concretes

Durability enhancement of low-carbon alkali-activated cements, as an emerging alternative to portland cement, is imperative for optimal performance in various conditions. This study examines the influence of one-part and two-part activators ( Na 2 SiO 3 · 5 H 2 O , Na 2 SiO 3 -anhydrous, and NaOH + Na 2 SiO 3 ) on the long-term performance of alkali-activated slag concretes exposed to a 5% magnesium sulfate ( MgSO 4 ) solution for 450 days at 23 ° C ± 2 ° C . Experimental results show that the mixture activated with Na 2 SiO 3 -anhydrous exhibits compressive strength 17% and 7% higher than the NaOH + Na 2 SiO 3 and Na 2 SiO 3 · 5 H 2 O mixtures, respectively, after prolonged sulfate exposure. Its electrical resistivity decreases by 32.7%, compared to reductions of 46.8% and 44.6% for the two-part and pentahydrate mixtures. Mass loss after 450 days was 3.5% for Na 2 SiO 3 -anhydrous, 4.8% for Na 2