Effect of volcanic ash pozzolan or limestone replacement on hydration of Portland cement

The replacement of Portland cement (PC) with either supplementary cementitious material (SCM) or fillers, such as natural pozzolans (NP) or limestone powder (LP) respectively, is known to affect the chemical properties of concrete, thus influencing its fresh and hardened properties. This study investigated the effects of volcanic ash NP or LP on setting time, normal consistency, hydration, and strength properties of cement paste and mortar while following the chemical changes that were a direct result of the substitution. While both materials were found to increase water demand, NP at 30% and 50% replacement levels increased setting time while LP at 15% replacement level insignificantly influenced the property. At a proportion lower than their replacement levels, both materials reduced the ultimate compressive strength of mortar. Thermal, chemical and microstructural analyses confirmed the participatory roles of NP and LP in controlling reaction kinetics and forming new hydration products.