Pozzolanic activity and alkaline reactivity of a mordenite-rich tuff

A natural mordenite-type zeolite from Palmarito ore deposit (Cuba) was studied along the reaction with a saturated lime solution at 40 °C in order to determine its pozzolanic activity. Ca(OH)2 is an alkali activating agent that simulates the release of lime from ordinary portland cement during the hydration reaction. Formation of C–S–H-like phases with very low Ca/Si ratio (below 0.8) was observed in agreement with previous studies, however, the transformation of the original mordenite into a heulandite–clinoptilolite-type secondary zeolite was also detected. A thermodynamic approach was used to evaluate the stability of the zeolite minerals and showed that clinoptilolite is the most stable zeolite that forms under the experimental alkaline conditions. The results indicate that not all Ca2+ consumed from solution is used in the pozzolanic reaction. Calcium aluminates hydrates were not detected as products of the alkali-activated reaction.