Surface-modification of fly ash and its effect on strength and freezing resistance of slag based geopolymer

The surface of Grade III fly ash particles was modified by addition of gypsum and mineralizing agent (anhydrous calcium chloride) at 960 degrees C for 2 h. The mineral phase formation, structure and chemical compositions of the modified fly ash were analyzed by XRD, FESEM and EDS. Moreover, the influences of surface-modified fly ash on the compressive strength and freezing resistance of slag based geopolymer were also investigated in this work. The results showed that the beta-2CaO center dot SiO2 (beta-C2S) and 3CaO center dot SiO2 (C3S) phases were formed on the surface of fly ash particles after surface-modification. When adding modified fly ash into slag based geopolymer, due to the filling effect and functions of active agents (beta-C2S and C3S), the strength and freezing resistance were improved markedly compared with that of the geopolymer added with original fly ash. (C) 2018 Elsevier Ltd. All rights reserved.