Thermal and structural micro analysis of micro silica blended fly ash based geopolymer composites

The effect of micro silica addition at 0, 5 and 10% on fly ash geopolymer composites; paste, mortar and concrete prepared using the hybrid solution of sodium silicate and sodium hydroxide cured at 80 degrees C for 24 h, aged for 7 days studied under elevated temperature. The incorporation of micro silica at 5% level increase the composite strength at room temperature, and it is pronounced in the paste at 800 degrees C (50% Strength gain). Thermal stability of the composites was studied using TGA/DTA analysis till 1000 degrees C. The linear dimensional stability of paste and mortar maintained till 800 degrees C without any physical damage. 10% of micro silica addition exerts more filling effect that damage the integrity of the bulk specimen of mortar and concrete thereby decrease the compressive strength. The XRD pattern of paste 0% (M1) and 5% micro silica (M2) confirms the presence of secondary hydration product of semi-crystalline Hydroxysodalite Na4Al3Si3O12OH at room temperature. The higher intensity of Nepheline (NaAlSiO4) and Albite (NaAlSi3O8,) phases in the M2 at 800 degrees C represents the Si and Al-rich N-A-S-H corroborated with the observed chemical shift of Q(4)(4Al) in Si-29 MAS-NMR and the resonance peak shift towards 60 ppm Al(IV) from 0 ppm (Al(VI)) in Al-27 MAS-NMR. The symmetric and asymmetric stretch of T-O-Si (T=Si/Al) band in ATR FT-IR spectrum of M1 and M2 compared to verify the geopolymer network.