Thermal treatment and pozzolanic activity of Na- and Ca-montmorillonite

Samples of both untreated and calcined (at about 730, 830 and 930 degrees C) Na- and Ca-montmorillonite, before and after having reacted with Ca(OH)(2) in the presence of simulated cement pore solution, were studied with XRD, SEM, EPMA and for chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the (un)calcined montmorillonite-cement mortars were studied with rheological properties and compressive strength tests after reaction for 2, 7, 28 and 91 days. The study indicates that the montmorillonites are fairly good pozzolanic materials and calcination substantially improves their pozzolanic activity. A clear optimum calcination temperature is 830 degrees C for both Na- and Ca-montmorillonite.