Influence of Calcined Clay on Workability of Mortars with Low-carbon Cement

The second-largest industrial global emitter of CO2 (Carbon dioxide) is the cement sector. The technology roadmap of low carbon transition for cement industries includes the introduction of calcined clay (CC) as supplementary cementitious material. A new type of alternative binder, called Limestone Calcined Clay Cement (LC3), was recently proposed. This cement can reduce CO2 emissions of cement production by up to 40% and it is prepared using limestone (LS) and clay which are globally available. Many scientific studies aimed to investigate the hydration of LC3 to understand the contribution of CC to the development of the compressive strength. However, recent studies showed that other cement properties, like workability and water demand, are highly impacted by calcined clay. Despite some papers state that an increase in superplasticizer (SP) dosage compensate this effect, such concrete is usually sticky, and hard to handle and deal with. In this sense, a proper understanding of the mechanisms regulating rheology of LC3 is needed. The objective of this study is to analyze workability of CC-based cement pastes and mortar, specifically investigating the role of free water in particle suspensions. Preliminary results show that CC highly influences workability of mortars and pastes. The flow table test results highlight a need to increase SP dosage to achieve target workability with CC cements. Differential scanning calorimetry (DSC) and 1 H time domain-nuclear magnetic resonance (TD-NMR) results clarify that the capillary unbound water is rapidly consumed by CC, being thus unavailable to fluidify cement pastes. This multi-method approach provides a further step in understanding CC impact on workability of mortars with low-carbon cement and opens new ways to understand paste, mortar, and concrete workability.