Assessing hydration kinetics and rheological properties of Limestone Calcined Clay Cement (LC3): Influence of clay-mitigating and superplasticizer admixtures

Limestone calcined clay cements (LC3) signify a trend in the construction sector aimed at reducing environmental impacts. However, the fresh state behavior of these cements, especially concerning clay properties and their interaction with chemical admixtures, needs to be better understood and investigated. This study is designed to assess the impact of a polycarboxylate-based superplasticizer (ADV) and a clay-mitigating (CM) admixture, along with exploring the synergistic effects that arise from combining both admixtures on the properties of LC3 cements. Hydration kinetics were evaluated in cement pastes using isothermal calorimetry and in-situ XRD, while fresh state properties were evaluated by rotational rheometry. The calorimetry results showed that the CM admixture provides a delay in the aluminate reactions of all LC3 systems, while it does not significantly affect the hydration of Portland cement pastes, suggesting a pronounced interaction of this admixture with clay particles. The incorporation of the CM admixture did not yield favorable workability conditions in LC3 mixtures when compared to the effectiveness of the ADV. In general, the assessment indicates that the CM admixture lacks effective dispersion capabilities and exhibits a limited influence on the formation of hydrated products in LC3 cements produced with calcined kaolinitic clay.