This research was conducted in cooperation with the Ban San Bun Reung Community Enterprise Group, which produces and distributes common clay bricks throughout northern Thailand. The ongoing aim is to develop thermal–acoustic fired clay bricks. In this study, charcoal was selected as an additive during brick manufacture owing to the ease with which its particle size can be reduced and its tendency to burn out during firing. Four different sizes of charcoal, namely, large (2 mm), medium (1 mm), small (0.5 mm), and fine (0.04 mm), were investigated. The charcoals were added to the clay mixture in various amounts, such as 0, 5, 15, and 30 wt%. The extruded brick specimens were then fired at 900, 1000, or 1100 °C, and their physical, mechanical, thermal, and acoustic properties, mineralogical composition, and microstructure were examined. Subsequently, linear regression and multiple linear regression analyses were applied to model the relationships between the brick properties and one or more explanatory variables. The results obtained revealed that the mechanical properties of the fired clay bricks improved with increasing firing temperature owing to the formation of the mullite phase. However, the mechanical properties rapidly deteriorated as the proportion and size of the charcoal additive were increased. The linear and multiple linear regression analyses demonstrated that the physical properties were correlated with the other properties evaluated in this study. In terms of the physical and mechanical properties, the use of 15 wt% of small charcoal and firing temperature of 1100 °C were the optimal conditions for manufacturing clay bricks satisfying the Thai Industrial Standard. In contrast, the use of 30 wt% of large charcoal and firing temperature of 1100 °C afforded lower thermal conductivity and a higher sound absorption coefficient owing to the more porous nature of the resulting bricks. The current production cost and sale price of traditional clay bricks are 53.58 and 264 THB m−2, respectively. When added with charcoal, the price increases to 55.17, but we expect that thermal–acoustic bricks could attract a higher price.
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Jul 8, 2020
Patcharaporn Chaipattanamatee 
Open Access