Comparative study of accelerated decalcification process among C3S, grey and white cement pastes

Abstract

This study compared the resistance of Triclinic-C3S, grey (OPC) and white (WOPC) Portland cement paste to decalcification induced by accelerated leaching in concentrated ammonium nitrate solutions. Paste microstructure was studied with scanning and backscattering electron microscopy (SEM and BSEM) and nitrogen BET surface area techniques. Ca2+ leached content was quantified by ICP, XRD and FTIR techniques were used to study phase mineralogy. The conclusions drawn from the findings were that calcium leaching-induced decay in the cementitious materials studied (C3S, OPC and WOPC), accelerated by immersion in ammonium nitrate, affected the main calcium phases in the samples (CH, C–S–H gel and ettringite), i.e., both the anhydrous and the hydrated phases. The present study showed that the Ca/Si ratio of C–S–H gels declines on a gradient from the sample core outward. Specimen surface area and nanoporosity rose in cementitious materials after Ca leaching-induced decay and subsequently declined as a result of the collapse of the structure of the hydrated cement, and in particular of the C–S–H gel. C3S paste was impacted more quickly and intensely by leaching than the WOPC and OPC pastes. Further to the findings of this study, the leaching resistance of these three materials, in descending order, is: OPC > WOPC > C3S.