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

Abstract

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 microscopic 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 properties with the material's carbonate content, and the inability of large quartz with interface cracks to take over any mechanical loads.