Analysis of tempered bricks: from raw material and additives to fired bricks for use in construction and heritage conservation

Abstract

Throughout history, human civilizations have combined clay soils with additives to produce better brick building material. Recently, bricks have been used as a method of eliminating industrial and agricultural wastes by incorporating the waste into brick raw mixtures. In this paper, the effects of three additives on the clay mixture and the fired bricks have been studied. Clayey soil from Jun (Granada, Spain) was combined with fly-ash, household glass and spent beer grain in manually made bricks fired at 800 ºC, 950 ºC and 1100 ºC. Differences in mineral composition, porosity, water behavior, mechanical resistance and color were analyzed through chemical, mineralogical, textural and physical analyses. The presence of carbonates in the clayey soil favored the formation of Ca (–Mg) silicates such as gehlenite, diopside and anorthite in the fired bricks. Only bricks with fly ash displayed growth of secondary acicular calcite crystals. Overall, the additives altered brick porosity and compactness. Bricks made with added glass were found to be the most compact and resistant bricks while those made with spent beer grain were the most porous and fragile. These results have important implications for the construction industry and for the conservation of architectural heritage.