Continuum micromechanics model for fired clay bricks: Upscaling of experimentally identified microstructural features to macroscopic elastic stiffness and thermal conductivity

Quantification of elastic stiffness and thermal conductivity of fired clay bricks is still often limited to empirical rules and laboratory testing, which becomes progressively more challenging given the large variety of raw materials used to optimize the properties of modern brick products. Applying a continuum micromechanics multiscale approach, we herein aim at upscaling of microstructural features to quantify the bricks' macroscopic properties. Microstructural features such as assemblage and morphometry of mineral phases (quartz, feldspar, and micas), of pores, and of the binding matrix phase, respectively, as well as thermoelastic phase properties are provided by recently published results from extensive micro-scopic testing including electron microscopy imaging, mercury intrusion porosimetry, nanoindentation, and scanning thermal microscopy. These results are incorporated into the micromechanics model by introducing spheroidal phases with characteristic orientation distribution at two observation scales. The homogenized macroscopic stiffness and conductivity agree very well with independent results from novel macroscopic tests for all seven studied brick compositions. This corroborates the microstructure-informed multiscale model approach and its assumptions: the linear increase of the binding matrix prop-erties with the material's carbonate content, and the inability of large quartz with interface cracks to take over any mechanical loads. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Automated summary

In this study, a continuum micromechanics multiscale approach was employed to upscale microstructural features to quantify the macroscopic properties of fired clay bricks. By introducing spheroidal phases with characteristic orientation distribution at two observation scales, the homogenized macroscopic stiffness and conductivity matched well with independent results from novel macroscopic tests for all seven studied brick compositions. This validates the microstructure-informed multiscale model approach and its assumptions, such as the linear increase of binding matrix properties with carbonate content and the limitations of large quartz with interface cracks in bearing mechanical loads.