Influence of Limestone Powder as Activator on the Enhancement of Early Mechanical Strength and Durability of High Blending Fly Ash Mortar Cured Under Different Temperatures

The early mechanical strength of high blending fly ash (FA) concrete in the hardening process is extremely low and greatly affected by curing temperatures, which seriously affects the construction speed and durability. To solve this problem, the influence of limestone powder (LS) as an activator on the enhancement of early mechanical strength and durability of high blending FA mortars cured under 5, 20, and 50 °C was investigated. The results reveal that LS can increase the early compressive strength of mortars with 30% FA cured under 5, 20, and 50 °C at 3 d by up to 21.0%, 18.2%, and 21.2%, respectively. Meanwhile, FA mortar with LS cured under 20 °C can achieve a maximum resistance to freeze-thaw cycles and chloride ion erosion, followed by under 50 °C and 5 °C. Under high curing temperatures of 20 °C and 50 °C, the nucleation effect of LS is more conducive to the cement hydration in FA mortar to produce more hydration products and the microchemical activity of LS can facilitate CaCO₃ from LS to react with calcium aluminate in cement to form calcium carboaluminate (Mc). However, a low curing temperature of 5 °C will significantly reduce the nucleation effect and microchemical activity of LS, causing LS to act more as a filler in FA mortar. LS as an activator can promote more hydration products in FA mortars and make the inner structure of FA mortar denser. LS can greatly reduce the total porosity of FA mortar cured under 20 °C and 50 °C.