Durability of alkali-activated slag concrete with sodium metasilicate powder as activator under nitric acid attack

The study presented here examined the durability and microstructural properties of one-part alkali-activated slag concrete (AASC) exposed to a nitric acid environment (pH = 1). The alkali activators employed included sodium metasilicate pentahydrate (Na2SiO3<middle dot>5H2O) and anhydrous sodium metasilicate (Na2SiO3-anhydrous). Various parameters were explored, such as compressive strength, electrical resistivity, mass and volume changes, and acid penetration depth. X-ray diffraction, scanning electron microscopy images, energy dispersive X-ray (EDX) analysis and elemental mapping were also used to monitor microstructural changes. The results showed that one-part alkali-activated slag concrete made with anhydrous sodium metasilicate in a nitric acid medium had relatively better performance than the same concrete activated with sodium metasilicate pentahydrate. Microstructural analysis showed that due to the nitric acid medium, the composition of binder gel atoms changed, but no new phase was created in the concrete matrix. Based on the findings derived from EDX analysis, it could be inferred that the greater abundance of sodium and magnesium elements in one-part AASC, in comparison to the ordinary Portland cement (OPC) mixture, contributed to a retardation in concrete destruction. In addition, the OPC mixture displayed mass and volume changes 2.43 and 2.64 times greater than those of the one-part AASC activated with anhydrous sodium metasilicate.