Effect of pozzolans on the hydration process of Portland cement cured at low temperatures

The aim of this paper is to study hydration processes in cement pastes and mortars, blended with either metakaolin (MK) or a catalyst used in catalytic cracking (FCC), and cured at low temperature. The amounts of hydrates and portlandite in pastes have been determined for 3–28 days curing at 5–20 °C. Microstructural study, using thermogravimetric analysis of the pastes, has shown that FCC acts mainly as a pozzolan at low temperatures (5–10 °C), whereas MK also accelerates Portland cement hydration. Mechanical strengths of a control mortar, and mortars made with 15% replacement of cement by these two pozzolans, have been measured. Both mortars containing pozzolans exhibited a relative increase in compressive strength when cured at 5 °C. A limestone filler (LF) has been used to compare the effects of adding inert or pozzolanic materials. Finally, mortars were prepared by partially replacing aggregates with either MK, FCC or LF. The MK and FCC are effective materials even for low curing temperatures, especially when they are used to replace a fraction of the aggregates in mortars.