Model for Characterizing Rheological Behaviour of Fresh Mortar and Conrete

Abstract

<p>Rheology of fresh mortar and concrete affects the flow of the mixture as well as the corresponding rheological properties. The rheological properties, in tum, are known to affect the placement and workability of the fresh mixture, and therefore can be used to control the quality of the fresh material and the properties of the hardened material. Accordingly, constitutive equations for fresh mortar and fresh concrete were developed to characterize the mixture flow and quantify the rheological properties. Moreover, by incorporating the mixture composition into the constitutive model, one can provide the concrete industry with the necessary tools to design and control the quality of concrete.</p> <p>This study presents a constitutive material model for mortar and concrete that employs the cell method and builds on the work of Gang et al. It postulates that the shear stress is the sum of three components: static interaction between particles, dynamic interaction between particles, and collision ofparticles, and that the cell is a representative volume of mixture. For fresh concrete, the effects of particles collision are considered negligible due to high particles concentration, and the resultant constitutive equations become the Bingham model.</p> <p>Two new models were developed to quantify the rheological properties of fresh concrete, namely plastic viscosity and yield stress. The plastic viscosity model postulates that the cell is a representative volume and that the packing density of the mixture can be used to characterize the aggregate's geometric and physical properties. The model is then extended, to model yield stress following the analogy concept. Evaluation of the proposed models was carried out by comparing their predictive capabilities to experimental data as well as to results of rheological models proposed in the literature. Results revealed that the proposed models provide a higher degree of correlation to the experimental data as well as a more consistent and reliable predictions in comparison to the models currently proposed in the literature for concrete and/or dense suspensions.</p> <p>The proposed constitutive equations for fresh mortar were also evaluated using experimental data reported in the literature. The results are found to compare very well and that the difference is within the measurement errors.</p>