Fluorescence microscopic investigation of PCE superplasticiser adsorption in calcined clay blended cement

Global efforts to minimise carbon dioxide emissions are also leading to attempts to use calcined clays (CC) as a partial substitute for cement in concrete. While the hydration mechanism of such CC blended cements is now well understood, the range of effective admixtures like polycarboxylate ethers (PCE) is limited. There are PCE types that promise relatively high effectiveness, but the mechanisms of action are not yet sufficiently understood. For a detailed understanding of the adsorption of such PCEs, spatially resolved studies of the binder were performed using a combination of fluorescence and scanning electron microscopy. In a comparison of two superplasticisers, the investigations have shown different sites of preferred adsorption in a CC blended system and the results can be correlated with flow tests and setting behaviour. The investigations have shown that a certain PCE type has a higher adsorption on CC and other components of a blended system in comparison to other types. Efforts to reduce carbon dioxide emissions globally are driving attempts to use calcined clays as a partial replacement for cement in concrete. Although the hardening mechanism of cements blended with calcined clays is well understood, the range of effective admixtures, such as plastisicing agents, is limited. While some plastisicing agent types show relatively high effectiveness, their mechanisms of action are not yet fully understood. To understand how these plastisicing agents interact with the compounds, fluorescence and scanning electron microscopy has been used to study this interaction. Two different plastisicing agent types have been compared and it was found that they prefer different sites of the compounds to interact with in a blended cement. These results can be correlated with flow tests and setting behaviour. The investigations have shown that one particular type of plastisicing agents has a higher affinity to calcined clay and other components of a blended system compared to other types.