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Microstructure-at-rest evolution and steady viscous flow behavior of fresh natural pozzolanic cement pastes

Abstract:

Portland cement without any class of admixtures and additives was substituted with a mixture of volcanic ash (VA) and pumice powder (PP) to obtain volcanic Portland cement (VPC) with four different compositions. Three water/binder ratios were considered (0.40, 0.45, and 0.50). A non-destructive rheological test was used to determine the evolution with the rest time of the microstructure-at-rest build in each cement paste. Steady flow curves showed that VPC pastes are non-linear viscoplastic materials, the non-linearity being depending on the water/binder ratio and the binder composition. After a discussion on different models, the modified Bingham model was used for fitting the experimental data. A maximum shear rate for the stable flow field is pbkp_redicted. A new physical meaning for the plastic viscosity was proposed, and the segregation resistance was instead quantified with the apparent viscosity evolution with shear. Stronger and faster built microstructure-at-rest was observed when the cement substitution in VPC pastes is higher. The yield stress, the plastic viscosity, and the second order coefficient increased with cement substitution. These results were justified on basis of the different specific surface area and density of Portland cement and volcanic pozzolan used in this study.