Compressive strength and microstructural characteristics of class C fly ash geopolymer

Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO2/Na2O Was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na2O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were Cured at 75 degrees C for 8 h followed by curing at 23 degrees C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm(-1) have been attributed to asymmetric stretching of Al-O/Si-O bonds, while those at 747 cm(-1) are due to the Si-O-Si/Si-O-Al bending band, The main geopolymeric gel and calcium silicate hydrate (C-S-H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM-EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern. (C) 2009 Elsevier Ltd. All rights reserved.