Effect of curing conditions on hydration reaction and compressive strength development of fly ash-cement pastes

Fly ash is one of the pozzolanic materials which has been widely used to effectively improve the various properties of concrete. The reaction between pozzolan and calcium hydroxide is referred to as the pozzolanic reaction. The product of the pozzolanic reaction, calcium silicate hydrates (C-S-H), is highly efficient in filling up large capillary spaces due to its lower density which is lower than that of C-S-H produced from the reaction of Portland cement and water. Thus, it improves the strength and impermeability of cementbased materials. The term for curing of concrete stands for procedures devoted to hydration reaction of cement and pozzolanic reaction of the fly ash, consisting of control of time, temperature, and humidity conditions. Several studies have undergone to understand the influence of curing on the compressive strength of the fly ash concrete. In addition, it has been reported that the fly ash concrete is more sensitive to curing conditions and requires a longer curing period than that required by OPC concrete. However, the mechanism on the effect of curing conditions on the strength development is yet to be ascertained. Due to their hydration characteristic, both pozzolanic reaction and the reaction of Portland cement require water to complete their reaction. The prevention of rapid and excessive loss of water occurring during the evaporation process in the early age is necessary for the adequacy of water for the slower pozzolanic process.