Effect of multi-factors on the performance of one-part geopolymer mortar against magnesium sulfate erosion

Buildings in coastal areas have suffered from seawater immersion and tidal erosion for a long time, and the resistance of building structures to sulfate erosion has always been a concern. To solve this problem, an attempt is made in this paper to develop a new low-carbon-dioxide green geopolymer cementitious material that is resistant to sulfate attack. The effect of this geopolymer material on sulfate erosion resistance is investigated in terms of alkali admixture, alkali modulus, water–binder ratio and fly ash admixture. In this paper, the geopolymer materials were tested for sulfate erosion resistance by dry–wet cycle sulfate erosion mechanism. It was shown that the contribution to improving the resistance of geopolymer materials to magnesium sulfate (MgSO₄) attack can be ranked as follows: water–binder ratio > fly ash content > alkali content > alkali modulus. Increasing the alkali admixture, water–binder ratio and fly ash admixture and decreasing the alkali modulus will promote the generation of gypsum in the specimen; Mg²⁺ in magnesium sulfate solution makes the volcanic ash reaction products decalcify, and the free Ca²⁺ and [SO₄]²⁻ combine to generate gypsum, causing gypsum-type erosion damage in the specimen.