Properties of quicklime(CaO)-activated Class F fly ash with the use of CaCl2

This study reports the significant effect of CaCl2 on strength improvement in CaO-activated Class F fly ash system. In these systems, the presence of CaCl2 promotes (1) a higher degree of fly ash dissolution, (2) increasing C-S-H formation, and (3) an overall reduction of pore size and volume, resulting in increased strength. However, while more C-S-H, which is responsible for strength increase, was produced with higher CaCl2 content, extreme doses of CaCl2 resulted in strength degradation; more importantly, the best quantity of CaCl2 for the greatest strength was dependent on the water-to-binder weight ratio (w/b). This dependency was closely related to the formation of calcium oxychloride, which generally causes severe expansive cracking and depends on w/b.