Compatibility studies of N-A-S-H and C-A-S-H Gels in Alkali-Activated Geopolymer Mortar

The primary reaction products in the alkali-activated green tuff alumino-silicate geopolymer mortar are Natrium (sodium) Aluminum-Silicate Hydrate (N-A-S-H) and Calcium Aluminum-Silicate Hydrate (C-A-S-H) gels. The alkaline activation was achieved using NaOH with a molarity of 4 mol/dm3 and sodium silicate with a ratio of 2.3–2.4. Alkaline activators represent a possible solution for a sustainable environment and reducing CO2 emissions. The presence of sodium hydroxide with higher alkalinity indicates the decomposition of sodium at an older age, as seen in SEM-EDS, XRD, XRF, and FT-IR analyses, and eventually cracking. The main phase present in the alkali-activated green tuff mortar with the optimal sodium hydroxide with a molarity of 4 mol/dm3 are calcium silicate hydroxide hydrate (Ca4.5Si6O15 (OH)3 2H2O), sodium calcium aluminum silicate hydrate (Na3Ca3.36Al9.68Si26.56O72 (H2O)24.48), zeolite (Si8Al4Ca2O24 (H2O)12), sodium silicate hydrate (Na4.12Si36O72 (H2O)23.12) and sodium aluminum silicate hydrate (Na4.12Si36O72 (H2O)23.12). At the initial stages, calcium in slag from the forging furnace stabilizes (N, C)-A-S-H gels, causing C-A-S-H gels to predominate over N-A-S-H. Over time, the trend reverses, with N-A-S-H becoming dominant. Ternary compositional diagrams show the range of chemical elements and the assemblage of resulting phases (minerals) at 180 days of age.