*4.2. Compressive Strength of Mortars*

The compressive strength of mortar with GGBFS replacement ratio at each curing temperature is shown in Figure 3. The compressive strength of mortar at an early age is found to be lowest with increasing GGBFS replacement ratio. However, with an increase in curing temperature, the compressive strength is increased. It is reported by Karim et al. that supplementary cementitious materials (SCM) in cement significantly modify the hydration kinetics and gives better performance at higher curing temperature [55]. However, the long term strength of blended cement mortar depends on curing temperature. Moreover, SCM can recover the strength once it cured in high temperature at longer duration. The early strength of higher GGBFS replacement mortar is lower, but it can be improved when it would cure at elevated temperature attributed to the quick cement hydration reaction. At 5 ◦C curing temperature, the compressive strength of 50% GGBFS mortar exceeded the compressive strength compared to 30% GGBFS after 39 days (Figure 3a). In addition, at 20 ◦C (Figure 3b) and 35 ◦C (Figure 3c) curing temperature, the compressive strength of 50% GGBFS mortar exceeded compare to OPC after 28 and 22 days, respectively. As the GGBFS replacement ratio increases, the crossover effect of compressive strength is delayed compared to OPC. However, the crossover effect of compressive strength decreases as the curing temperature increases. Therefore, depending on the replacement ratio of GGBFS, the hydration and degree of hydration of mortar are very sensitive to temperature.

**Figure 3.** Compressive strength of mortar, according to curing temperature and replacement ratio of GGBFS (**a**) 5 ◦C, (**b**) 20 ◦C, (**c**) 35 ◦C.
