This paper presents the results of an experimental study on the microstructure, the thermal and the mechanical properties of a clay-based ceramic used in building applications. The X-ray tomography analysis showed a layered microstructure of clay with 200 µm sheets of porosity after the extrusion process. The gas release from the dehydration, dehydroxylation and decarbonation induced a 7 vol% formation of porosity during the heat treatment of the clay-based ceramic up to 850°C. The porosity increase and the development of metakaolin led to a 38% decrease in the thermal conductivity. On the other hand, the Young's modulus of the clay-based ceramic was conserved due to the formation of smaller pores than the 200 µm sheets of porosity. The densification and the crystallization of amorphous phases also led to a 110% increase of the Young's modulus from 850°C to 1050°C. The Young's modulus of the clay-based ceramic was only decreased by the β→α quartz inversion of the cooling due to sand addition. Hence, this study provided a useful insight into how the microstructure of fired clay bricks can be specifically transformed by the porosity during the heat treatment to control the thermal and mechanical properties.

This research investigated the impact of the particle shape of organic additives on the anisotropy of a clay ceramic and its thermal and mechanical properties. The impact of the particle shape was elucidated by addition in the clay ceramic mixture of Olive Stone Flour (OSF) in the form of powder and Wheat Straw (WS) in the form of fibers. The OSF powder reduced the clay ceramic anisotropy with a formation of round shape pores during the firing process. The flexural strength of the clay ceramic was improved by 13% in case of an 8 wt% addition of OSF. On the other hand, the WS fibers increased the anisotropy by the formation of orientated pores along the extrusion plane. The thermal diffusivity of the clay ceramic was improved by 41% in the direction of the thermal gradient of the walls in case of an 8 wt% addition of WS. Hence, this study proved the particle shape of the organic additives as a useful parameter to control the anisotropy of clay ceramics and improve their thermal and mechanical properties.