Investigation on early hydration of ternary Portland cement-blast-furnace slag–metakaolin blends

• Initial hydration of PC–BFS–MK ternary system is influenced mainly by PC and MK.
• MK accelerates the hydration of clinker minerals.
• The third peak on calorimetric curve is related to formation of hemicarbonate.
• Hemicarbonate is formed as a product of conversion of ettringite.

The paper investigates the hydration of ternary blends comprising Portland cement, blast-furnace slag and metakaolin. The isothermal calorimetry and “in situ” X-ray diffraction was used to evaluate the effect of metakaolin and blast-furnace slag on the early hydration of blends. XRD, DTA and SEM were used to analyze the hardened paste after 1 month of hydration. Metakaolin influences significantly the kinetics, mechanism and products of hydration at initial period of hydration causing the rapid formation of ettringite. Hemicarbonate aluminate hydrate is formed as a product of ettringite conversion due to the presence of reactive calcite in Portland cement.