Effect of cement type on metakaolin efficiency

It is acknowledged in the literature that the performance of supplementary cementing materials such as fly ash or silica fume often depends on the characteristics of the cement used. This work aims to show that this dependence also concerns metakaolin. Compressive strength tests were carried out between 2 days and 2 years using one flash metakaolin and a panel of 11 cements having a wide range of characteristics. At 28 days of age, the difference in terms of strength activity index could reach 0.4 between the most and the least efficient cements. The hydration of MK pastes followed by XRD and thermal analysis showed that the pozzolanic reaction involving MK was postponed with low-C3A cements, as characterized by a delay of portlandite consumption and stratlingite formation. Several mechanisms are reviewed and discussed with the aim of explaining the role of cement in the development of the pozzolanic activity of MK.