Title: Understanding the Role of Calcined Clay on Pore Structure and Transport Properties of Cement Composites

Author(s): Yuvaraj Dhandapani

Publication: Web Session

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Date: 10/17/2021

Abstract:
The use of calcined clay as a substitute material has multiple effects on the evolving microstructure and significantly alters the durability performance of concrete systems. In this study, concretes prepared with calcined clay were characterized for resistance to chloride and moisture ingress using non-steady state chloride migration and unidirectional capillary absorption experiments, respectively. The studies were performed on a range of concrete prepared with a lower grade calcined clay (50% kaolinite content) as supplementary cementitious materials (SCMs) in binary and ternary forms along with fine limestone powder. Notably, the interaction of calcined clay positively influenced physical structure at an early age, i.e., 3 days, which was captured by mercury porosimetry and formation factor assessment. The chloride resistance of concretes prepared with calcined clay significantly improved, and the dilution of hydrates due to limestone addition was effectively neutralized by the synergistic interaction between calcined clay and limestone. Long term moisture ingress was studied using capillary absorption experiments for an exposure period of 28 days, and the results reveal that both binary and ternary binders containing calcined clay had a lower absorption rate than the OPC system. Unlike chloride ingress, the moisture uptake profiles were able to capture the difference caused due to limestone addition explicitly. The transport parameters were examined using estimates of pore network parameter, i.e., formation factor and tortuosity. Concrete prepared with calcined clay and the calcined clay-limestone combination had a higher tortuosity value, which explains improved transport properties using a physicochemical framework. The applicability of these pore network parameters could serve as a basis to conceptualize the link between reactivity, microstructural evolution, and transport characteristics in cement composites.