Comparison between curing conditions of zeolite and siltstone cement pastes at low W/B ratio after 91 days

Abstract

This study deals with a comparison between water and air cured blended cement pastes at a Water-to-binder (W/B) ratio of 0.3 after ageing for 91 days. Supplementary Cementitious Materials (SCMs) like zeolitic tuffs are widely used to improve compressive strength by the pozzolanic reaction. In this study, mordenite rich tuff, a mixture of clinoptilolite-heulandite-mordenite-calcite, and calcareous siltstone were blended with Ordinary Portland cement (OPC) at levels ranged from 5 to 27.5%. Using quantitative X-ray diffraction (QXRD), Thermal gravimetric analysis-Differential scanning calorimetry (TGA-DSC), as well as density measurements and compressive strength, some hydration parameters such as content of calcium hydroxide (CH), anhydrous cement phases, calcite, and water in hydrates, density and the mechanical performance were determined. The results showed that hydration process of blended cement pastes was uncomplete at ages as late as 91 days regardless of curing conditions. The air cured cement pastes showed a less content of CH, water in hydrates, and compressive strength, but instead a higher density and content of carbonate-like minerals with respect to their water-cured counterparts. The pozzolanic reaction scarcely proceeded at a W/B ratio of 0.3 regardless of curing condition. Among the SCMs, mordenite rich tuff blended cement pastes presented the best compressive strength values, when was cured under water; the others showed better values of compressive strength in air curing condition.