Effects of water-to-binder ratios (w/b) and superplasticizer on physicochemical, microstructural, and mechanical evolution of limestone calcined clay cement (LC3)

This study investigated the effects of water-to-binder ratios (w/b) and a commercial polycarboxylate ether (PCE)-based superplasticizer on various characteristics of limestone calcined clay cement (LC3). Zeta potentials, rheology, hydration kinetics, and chemical, microstructural, and mechanical properties were assessed. A low w/b of 0.25 significantly reduced the hydration of the LC3. LC3 attained a more negative zeta potential in water due to negatively charged clay. The admixture dosage requirement was higher for LC3 than Portland cement, attributed to a high surface area and water uptake for saturation of the calcined clay. The admixture slowed the early-age hydration, yet the resulting enhanced particle dispersion compensated the heat evolution at the w/b of 0.25. LC3 reaction products were mainly characterized as C-(A-)S-H, portlandite, ettringite, monosulfate, and carboaluminates. Their morphologies at the low w/b were less apparent due to space confinement and associated constriction on crystal growth. Despite a higher mesopore content, an LC3-based high-performance concrete could be designed to achieve a strength of more than 100 MPa.