On the Use of Sodium Chloride and Calcined Diatomite Sludge as Additives to Improve the Engineering Properties of Bricks Made with a Clay Earth from Jun (Granada, Spain)

Solid bricks manufactured out of clayey earth from a quarry near the city of Granada (Spain) were studied and compared with others to which two additives were added during the kneading of the raw material: Calcined diatomite sludge and sodium chloride. Samples with and without additives were fired at 800 °C, 950 °C, and 1100 °C. New mineral phases were formed in the bricks after firing. These included gehlenite, diopside, and plagioclase, which is gradually enriched in calcium, and microcline, which is transformed into sanidine. Mullite and molysite also appeared in the bricks made with added salt. Porosity increased substantially in the bricks that contained diatomite sludge, while the addition of sodium chloride accelerated the mineralogical transformations and caused sintering at relatively low temperatures of 800 °C. The bricks became more compact and less anisotropic as the firing temperature increased. This behaviour was less evident in the bricks with added diatomite sludge, which alters the orientation of the phyllosilicates. The bricks fired at 1100 °C had the best physical parameters. However, the bricks with added sodium chloride fired at 800 °C reached hygric and compactness values that were at least similar to bricks from the other groups fired at 950 °C