Dimensional Change and Strength of Mortars Containing Fly Ash and Metakaolin

The length change and strength of mortar containing metakaolin (MK) and fly ash (FA) were investigated. Cement was partially replaced with 0–10% MK and 0–60% FA. Mortar specimens were subjected to water and mist curing at $20°\text{C}$ and air curing at $20°\text{C}$ and 60% relative humidity. The results show that there is noticeable shrinkage in mortars subjected to air curing, especially during the first 28 days. Beyond that age, there is little change in length. Increasing FA content under air curing reduced shrinkage. The incorporation of both 5% and 10% MK with varying amounts of FA further reduced shrinkage especially at 10% MK. As what can be expected, all mortars subjected to water curing exhibited an increase in length. Expansion was reduced when FA was present in the mix. However, mortars containing MK exhibited an increase in expansion under water curing with and without the inclusion of FA. Generally, for specimens subjected to mist curing, an expansion occurs during the first 15–30 days and beyond this age, shrinkage begins to take place. Replacing cement with 5% or 10% MK increases the compressive strength of mortar. The pozzolanic reaction of FA seems to get reduced as a result of preferential MK activity.