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

• Published in: Journal of non-crystalline solids Vol. 499; pp. 117 - 130
• Main Authors: M., Sivasakthi, R., Jeyalakshmi, Rajamane, N.P., Jose, Rinu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2018
• Subjects: 27Al and 29Si MAS-NMR; Elevated temperature; Fly ash; Geopolymer; Micro silica; XRD; Micro silica; Fly ash; Geopolymer; Elevated temperature; XRD; 27Al and 29Si MAS-NMR
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2018.07.027

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 °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 °C (50% Strength gain). Thermal stability of the composites was studied using TGA/DTA analysis till 1000 °C. The linear dimensional stability of paste and mortar maintained till 800 °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 °C represents the Si and Al-rich N-A-S-H corroborated with the observed chemical shift of Q4(4Al) in 29Si MAS-NMR and the resonance peak shift towards 60 ppm Al(IV) from 0 ppm (Al(VI)) in 27Al MAS-NMR. The symmetric and asymmetric stretch of TOSi (TSi/Al) band in ATR FT-IR spectrum of M1 and M2 compared to verify the geopolymer network.
•Studied the thermal resistance of micro silica (5 &10%) blended fly ash composites•Aluminosilicate network formation analysed by ATR-FT-IR and 29Si, 27Al MAS-NMR•Micro silica addition improves the N-A-S-H gel formation•TGA/DTA, thermal conductivity and thermal strain of composites are evaluated•Geopolymer mortar presented excellent thermal stability up to 800 °C temperature