Deterioration of alkali-activated and Portland cement-based mortars under sulfur oxidizing bacteria corrosion

This study investigated the deterioration behavior of the metakaolin based alkali-activated mor -tar (MK-M), flay-ash-based alkali-activated mortar (FA-M) and granulated blast furnace slag pow-der-based alkali-activated mortar (SG-M) under simulated microbial induced acid corrosion (MIAC). For comparison, the MIAC induced corrosion of the Ordinary Portland cement-based mortar (OPC) was also studied. The pH variation of the corrosive solution (sulfur oxidizing bacte-ria liquid medium), visually observation, and mass loss were monitored to estimate the deteriora-tion. X-ray diffraction (XRD), scanning electron microscope (SEM) and thermogravimetric analy-sis (TGA) were used to analyze the composition and morphology of different samples. The results revealed that the three alkali-activated cement-based mortars displayed a higher alkalinity com-pared to the Portland cement-based mortar. MK-M and SG-M exhibited better resistance to MIAC with a smooth surface and without the formation of typical corrosives owing to the stable struc-ture of N-A-(S)-H and the lower content of calcium ion. However, SG-M suffered severe corro-sion, which was similar to OPC-M, with the formation of abundant gypsum and ettringite and vi-sually changed morphology for its high content of calcium ion and degenerated structure.