Durability of Cement Paste with Metakaolin

Durability characteristics of cement paste with two types of metakaolin (MK1 and MK2) replacement were examined. "Fluidized bed" calcination produced MK1 which was relatively pure, while "flash" calcination produced MK2, which had a high amount of quartz mixed in. At a 50% replacement after 28 days, porosity increased by 8.9 and 7% for MK1 and MK2 while primary sorptivity decreased. Thermogravometric and XRD analysis showed a decrease in the portlandite content by 79 and 75% for MKI and MK2, while the CaCO3 level did not change significantly. MK2, at an optimal replacement range of 5-30% produced relatively more CSH than MK1. Observed by SEM, metakaolin particles in MK2 were consumed by the pozzolanic activity more thoroughly than the particles of quartz. Metakaolin replacement levels of 20% or more for MK1, and 25% or more for MK2, made the cement paste very susceptible to carbonation ingress. Hydration stopping with propan-2-ol appeared to cause cracking while freeze-drying worked with no apparent problems. M