Natural pozzolan with different volcanic glass and zeolite content: Effect on the performance of blended cement

Abstract

Natural pozzolans containing zeolites are widely used as supplementary cementitious materials (SCMs). Zeolites are commonly found as a product of glass alteration in volcanic rocks such as tuffs and ignimbrites and are therefore often associated with these rocks. Volcanic glass is known to have a pozzolanic effect. Consequently, it is essential to understand whether the favourable performance of zeolites as SCMs is attributable to their zeolite content or the presence of volcanic glass. To this end, three natural pozzolans with varying zeolite and glass contents were examined as SCMs. The properties of the blended cements were analysed based on reactivity and hydration parameters to understand the effect of the alteration of volcanic glass to zeolites in natural pozzolans. The properties analysed were flow loss and mortar flow, heat release rate and compressive strength. The reactivity analysis was conducted using the Frattini test, combined water content and microstructural analysis by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The findings indicated that the extent of alteration resulted in a reduction inmortar flow and an acceleration in the hydration of OPC at an early age. Subsequently, the pozzolanic reaction of the glassy fraction serves to compensate for the dilution effect, contributing to the development of compressive strength. However, the zeolite fraction shows a very low pozzolanic reaction at 90 days.