Hydration characteristics of metakaolin—lime—gypsum

The hydration characteristics of some metakaolin—lime—gypsum mixtures were studied by the determination of their hydration products using XRD as well as DTA techniques. The effect of the phase constituents on the compressive strength of the hardened pastes was also investigated. The results revealed that at all ages of hydration the compressive strength increases with the increase in gypsum content up to 10% and then decreases. Generally, the compressive strength of these pastes increases with curing time. Pastes with 15 and 20% gypsum show an increase in strength for seven days and then deteriorate. The gehlenite hydrate is formed in pastes with small amounts of gypsum (5–10%), whereas the presence of enough gypsum (15–20%) prevents the formation of gehlenite with an increase in the ettringite phase.