Hydration Products and Reactivity of Blast-Furnace Slag Activated by Various Alkalis

Pastes of blast-furnace slag were cured for up to 90 d using sodium silicate (waterglass), NaOH, and three different mixtures of Na₂CO₃–Na₂SO₄–Ca(OH)₂ to activate reactions. The highest slag reactivity was observed for NaOH activation and the least for waterglass, although nonevaporable water indicated similar amounts of hydration products formed. The main hydration products found using X-ray diffractometry in all systems were calcium silicate hydrate (C-S-H) and a hydrotalcite-type phase. Microanalysis was performed on pastes activated using 50% Na₂CO₃·25% Na₂SO₄·25% Ca(OH)₂, NaOH, and waterglass; the chemical composition of the C-S-H in the waterglass case was different relative to the other two alkalis. For all alkaline agents used, the C-S-H seemed finely intermixed with a hydrotalcite-type phase of Mg/Al = 1.82, on average.