Thermal behaviours of clay mixtures during brick firing: A combined study of in-situ XRD, TGA and thermal dilatometry

• DOI: 10.1016/j.conbuildmat.2021.124319
• Publication Date: 2021-08-03T12:33:01Z
• Authors: Sen Wang; Lloyd Gainey; Daniel Baxter; Xiaodong Wang; Ian D.R. Mackinnon; Yunfei Xi
• Keywords: Thermal behaviour; Compressive strength; 02 engineering and technology; Clay mineral; In-situ XRD; 624; Phase transformation; 0210 nano-technology; Brick

Abstract The mineralogical transformation of clay material is critical to the firing process for brick manufacturing. In this study, a series of in-situ integrated techniques are used to study the properties of two clay mixtures routinely for production of bricks at a local factory in Queensland, Australia. In-situ XRD, thermal expansion/contraction, thermal weight loss, and microstructural evolution of brick bodies at high temperature have been investigated. Illite/mica persists until 950 °C during the firing process, while K-feldspar transforms into plagioclase with the addition of Ca cations from starting materials. A slower ramp rate decreases the onset temperature of many reactions, including the decomposition of calcite and nucleation/crystallisation of mullite. An increase of firing temperature from 950 to 1150 °C has significantly enhanced the compressive strength of the prepared brick buttons. In addition, six length changing steps have been identified across the temperature range from 30 °C to 950 °C. The contraction of kaolinite between about 420 °C to 850 °C might compensate for the thermal expansion of typical bricks, and may minimise the potential for failure during the α- to β-quartz inversion. However, the rapid shrinkage of metakaolin above 850 °C increases the risk of cracking in manufactured bricks.