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In blended cements, superplasticizers may distribute unevenly between the different mineral components, a challenge compounded by the heterogeneity of supplementary cementitious materials (SCMs). While it is understood that this may impact both rheology and hydration kinetics, the topic has not yet been addressed either systematically or quantitatively. This study does this by developing a quantitative framework called Pore Solution Matching (PSM), which enables systematic characterization superplasticizer distribution in multicomponent binders, using limestone calcined clay cement (LC3) as a representative system. This is done by using a polycarboxylate ether (PCE) and a diphosphonate superplasticizers. Protocols are established to conduct adsorption studies on the individual components of LC3, clinker, calcined clay, and limestone, to obtain results that represent an early-age LC3 paste. Integrating such data into a surface-based mass balance model it is possible to reconstruct polymer distributions and surface coverages across the different phases in LC3. As revealed by isothermal calorimetry this has important implications on hydration kinetics. Specifically, it is shown that the retardation response of LC3 varies linearly with the surface coverage of OPC by either of the superplasticizer used. Though demonstrated here for LC3, the methodology and insights presented are applicable to a broad class of SCM-rich binders, offering a generalizable strategy for admixture design in a broad range of cementitious systems, including but not limited to low carbon cements.
Moghul et al. (Sat,) studied this question.