Portland metakaolin cement containing dolomite or limestone - Similarities and differences in phase assemblage and compressive strength

The scarceness of high-quality limestone obliges the cement industry to consider alternative supplementary cementitious materials (SCMs) for the production of blended cements. This study investigated the potential usage of dolomite instead of limestone as an addition to Portland metakaolin cement by measuring the development of the compressive strength and phase assemblages at 5 °C, 20 °C or 38 °C. Laboratory grade materials were used to identify potential differences in the impact of the carbonate on the phase assemblages. As with limestone, a strength increase was observed when dolomite is added at temperatures >5 °C due to the formation of additional carbonate AFm phases and the stabilization of ettringite. Differences were observed in the amount and type of the carbonate AFm and AFt phases formed. Thermodynamic modelling in combination with the experimental results indicate that the dolomite and limestone affect Portland metakaolin cement in a similar way, with the reactivity being the major difference between the two carbonate sources. This indicates that with regard to the strength development up to 90 days dolomite can be used instead of limestone to replace parts of a Portland metakaolin cement.