Activation of LC3 binders by C-S-H nucleation seeding with a new tailored admixture for low-carbon cements

Abstract

The use of supplementary cementitious materials is currently the most favorable strategy for reducing CO₂ emissions in cements. Limestone Calcined Clay Cements, LC³, are a type of cement that allows the reduction of CO₂ emissions up to 40%. The proportions of the mixtures can vary, but the most investigated combination, LC³-50, contains about 50 wt% clinker, 30 wt% calcined kaolinitic clay, 15 wt% limestone and an optimised calcium sulphate content. However, the mechanical strengths of LC³ at early ages are not good enough and they should be improved. One way of doing this is by employing commercial strength-enhancing (accelerator) admixtures based on C-S-H nucleation seeding. For this work, LC³-50 cements were prepared with clays with varying kaolinite contents. Mortars and pastes were fabricated using a new PCE-based superplasticizer developed to avoid the loss of fluidity at early ages typical of LC³ binders. The selected accelerator for this study was Master X-Seed STE53. The results show that the loss of fluidity of LC³ mortars during the first hours could be solved by a recently developed PCE-based superplasticizer. The compressive strengths at 1 day for LC³ mortars strikingly improved by using the C-S-H seeding admixture and this behavior was maintained for up to 28 days.