Understanding the importance of carbonates on the performance of Portland metakaolin cement

Abstract

This study investigates the influence of different carbonate (limestone, dolomite and magnesite) and non-carbonate (fly ash, quartz and metakaolin) sources on the performance of Portland metakaolin cement binder. Mortar and paste specimens were cast for six binders comprising 50% clinker, 30% metakaolin, 5% gypsum and 15% of each of the carbonate and non-carbonate sources at a water to binder ratio of 0.5. Carbolaluminate phases were formed in binders containing any of the three carbonate sources. The beneficial effect of formation of carboaluminates was observed for early age (7 days) compressive strength values, however, the later age (90 days) compressive strength values were similar for all the binders. In the absence of the carbonate ions the formation of strätlingite was prominent, which is speculated to contribute in later age strength development. No appreciable difference was observed in the porosity, electrical resistivity or carbonation resistance between the binders containing carbonate or non-carbonate source at later age.