Study on the strength development, hydration process and carbonation process of NaOH-activated Pisha Sandstone

Pisha Sandstone which caused severe soil erosion is a kind of arenite formed during the Tertiary period in northwest China. Pisha Sandstone when combined with suitable alkali activators and mineral additives can be converted into alkali-activated cement. The compressive strength of alkali-activated Pisha Sandstone at different slag replacement levels, different NaOH dosages and ages were examined. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDS), Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to analyze the hydration process and carbonation process of alkali-activated Pisha Sandstone. TG/DTG was used to quantify the amounts of carbonates which formed from calcium silicate hydrate (C-S-H) at different steel slag additions and ages. The compressive strength of Pisha Sandstone with suitable activators (1% NaOH) and mineral additives (40% steel slag) can reach 46 MPa at 90 days. The results of SEM/EDS, FTIR, XRD and TG/DTG showed the products of NaOH-activated Pisha Sandstone are C-S-H gel and geopolymer gel. However it also showed serious carbonation of C-S-H gel. In particular, the results of TGA/DTG showed that the carbonation rate of tobermorite in C3 reached 37.8% at 28 days. But the carbonation rates of C-S-H gel decreased with the increasing of slag dosages and NaOH concentrations.