Multi-level diffusion model for manufactured sand mortar considering particle shape and limestone powder effects

Manufactured sand (MS) has been widely applied to concrete production due to the fact that the shortage of natural sand is becoming increasingly severe in China and many other countries. To predict the diffusion coefficient of MS mortar considering MS particle shape and limestone powder effects, a multi-level micromechanical model is proposed in this paper. MS mortar is represented as composite cement, powder-cement paste and MS mortar at three levels based on its multi-level microstructures. Homogenization procedures are performed at each level. The effects of limestone powder, including chemical and dilution effects, are respectively considered at the first- and second-level homogenizations. The shape of MS particles, characterized by its aspect ratio with ellipsoid assumption, is incorporated at the third-level homogenization. For verification, available data from experiments and existing models are employed. Results indicate that the proposed multi-level diffusion model is capable of estimating the diffusion coefficient of MS mortar. Finally, the effects of limestone powder content and MS particle shape on the diffusion coefficient of MS mortar are discussed based on the proposed diffusion model, which shows that the diffusion coefficient decreases with the increasing limestone powder content. Compared with the prolate and oblate shapes, MS mortar demonstrates the highest diffusion coefficient when MS particles are spherical. Oblate particle presents much more remarkable influence on the diffusion coefficient than prolate or spherical ones. (C) 2019 Elsevier Ltd. All rights reserved.