Macro and microstructural evolution of low-calcium fly ash-based geopolymer mortar exposed to sulphuric acid corrosion

This article reports an investigation of the behaviour of a low-calcium fly ash-only geopolymer (FAGP) mortar in comparison to Ordinary Portland Cement (OPC) mortar and a commercially available geospray mortar (P-GP) under laboratory-induced sewer conditions. An aggressive sewer condition was simulated by an accelerated corrosion rate, with mortar specimens immersed in 0.5pH sulphuric acid at a controlled temperature of 40 °C for 31 days. The macro and microstructural evolution of the specimens was analysed through visual observations, mass changes, and SEM coupled with EDS, XRD, and MIP analysis. OPC exhibited a 49 % mass loss attributed to the loss of the gypsum layer formed during the acid attack. The mass reduction in the low-calcium FAGP was only 6 %, which was 42 % lower than that of OPC, indicating that calcium-bearing hydrates in the cementitious binder systems are susceptible to sulphuric acid corrosion. The acid-resistant properties of FAGP mortar suggest its suitability for sewer rehabilitation applications.