Performance evaluation of clinoptilolite-rich zeolitized tuff before and after thermal calcination in cementitious systems

The increasing demand for sustainable construction materials has driven the development of supplementary cementitious materials (SCM) that can reduce the environmental footprint of portland cement. Clinoptilolite-rich natural zeolites are promising SCM due to their high silica and alumina content, yet their high porosity and variability can negatively affect fresh-state properties. This study examines the effect of thermal calcination (600 °C) on a zeolitized tuff to improve its performance as an SCM. The treatment temperature was selected based on TGA–DTA analysis. Both raw and calcined zeolites were characterized by XRD, FTIR, and SEM, and incorporated at 25 wt% cement replacement in blended systems. The experimental program included mini-slump tests, rotational rheometry, Fratini analysis, hydration kinetics, compressive strength, and electrical resistivity measurements. Calcination reduced yield stress by approximately 50%, improving paste workability, and produced a modest increase in compressive strength (up to 15.6%) without significantly altering pozzolanic reactivity. These findings indicate that calcination primarily enhances the rheological performance of natural zeolites while maintaining their chemical reactivity, providing a simple and effective route to optimize their use in sustainable cementitious systems.