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The structural build-up of cementitious paste with nano-Fe 3 O 4 under time-varying magnetic fields was experimentally investigated using small amplitude oscillatory shear (SAOS) technique. Several modes of magnetic fields, such as constant, sudden-changed and linearly-changed, were applied to the cementitious paste. Results showed that the structural build-up of the cementitious paste depended on the magnetizing time and magnetic field strength. Applying constant magnetic fields improved the liquid-like behavior during first minutes and afterwards the solid-like property was enhanced. Both the sudden-increased and sudden-decreased magnetic fields resulted in a sharp decrease in storage modulus. The linearly increasing magnetic field resulted in a slight increase in storage modulus but higher liquid-like behavior. When the magnetic field was linearly decreased from 0.5 T to approx. 0.25 T, the structural build-up was enhanced significantly, and with the continuously decreasing magnetic field from approx. 0.25 T to 0 T, a decrease in storage modulus was observed. [ABSTRACT FROM AUTHOR]

Polycarboxylate ether surperplasticizer (PCE) has been commonly used and studied to enhance flowability of cementitious materials. However, the effect of PCE addition on thixotropy and flocculation state has not gained enough attention. In this study, Focused Beam Reflectance Measurement (FBRM)-rheometer is coupled. The coupled setup could simultaneously measure both flocculation states in terms of chord length distribution of cement particles/agglomerates and rheological properties including dynamic yield stress and thixotropy. The effect of various PCE additions is explored, firstly by measuring the adsorption of PCE surfactants and the concentration of PCE surfactants in cement pore solution. It is found that the effect of PCE addition on dynamic yield stress, thixotropy and chord length distribution of paste particles/agglomerates are all bi-fold. The turning point is the Critical Micelle Concentration in cement pore solution. Results of more agglomerated flocculation states at low PCE addition are measured for the first time and further discussed. [ABSTRACT FROM AUTHOR]

In view of active rheology control of cementitious materials, nano-Fe 3 O 4 can be added as responsive particles. Following the concept of magnetorheological fluids, it is assumed that magnetic nanoparticles will form chains or clusters in cementitious paste following magnetic field lines. A quantitative experimental validation of this assumption is presented herein. The clustering of nano-Fe 3 O 4 particles under magnetic fields is studied by mapping iron (Fe) element distribution in cementitious paste using energy dispersive X-ray spectroscopy. By means of image analysis, the Fe-element patterns are quantified by the deviation of Fe-elements in a unit area from the mean value expected in case of a uniform distribution, as expressed by coefficient of variation (COV). The magneto-rheological responses of cementitious pastes are evaluated using small amplitude oscillatory shear technique. Results show that the magneto-rheological effect exhibits a linear relationship with the relative change of COV, providing a quantitative validation of magnetic clustering in cementitious paste. [ABSTRACT FROM AUTHOR]