Rheology of low clinker concretes with tailored superplasticizer polymers - Control and modelling of viscosity and thixotropic structural build-up

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To understand the fundamental mechanisms of properties of fresh cementitious materials, systematic research is required on the relationship between microstructure and the rheological properties of fresh cement paste. The aim of this research is to examine the effect of superplasticizer / particle interactions on the microstructure, viscosity and thixotropic structural build-up of cementitious suspensions.Understanding the internal structure of cementitious suspensions is not an easy task due to polydispersity, opaqueness, high solid fraction and hydration reactions. Thus, there is a lack of fundamental understanding of the intrinsic structure of fresh cement paste which is of great importance for the workability of concrete. Furthermore, the initial fresh state microstructure affects the microstructure of the hardened paste and consequently strength and durability [1]. The microstructure of a cementitious suspension is determined by the interparticle interactions. In simple terms, particles agglomerate when attractive interactions exceed repulsive interactions. Therefore, understanding the effect of superplasticizer on microstructure and obtaining a reliable estimate of the interparticle interactions in cementitious suspensions is a crucial step towards understanding the rheological properties.In this research, pastes and mortars will be prepared using specifically polymerized superplasticizers with either phosphonate or polycarboxylate functional groups and variations in backbone length, side chain length and side chain density. Viscosity and thixotropic build-up will be determined using rotational rheometry. Simultaneously, the evolution of microstructure is observed with an in situ laser backscattering measurement device (Dynamical Optical Reflectance Measurement with Selective Multi Depth Focus). Whereas, the kinetics of structural break-down in dependence of shear load is not addressed in this research. Finally, the effect of superplasticizer technology on microstructure as well as viscosity and thixotropic structural build-up will be discussed on the basis of colloidal surface interactions, hydration kinetics and a microstructural model.