Study of the mineralogical and textural properties of bricks with volcanic ash temper

Abstract

During the eruption of the Tajogaite volcano in La Palma (Canary Islands, Spain) in 2021, large amounts of pyroclastic material were emitted, which had severe environmental, health and economic impacts on nearby localities. One solution for the disposal of the volcanic ash that settled on the streets, roads, and roofs of La Palma is to use it as temper in brick production, which would also reduce the amount of clay required to make the bricks. Two different sizes (fine and coarse) and three percentages (10, 20, and 30 % by weight) of volcanic ash were added to a clayey sediment from Viznar (Granada, Spain) to produce bricks that were fired at 800, 950, and 1100 °C in an electric oven with an oxidising atmosphere. The chemistry, mineralogy and texture of the samples with volcanic ash were compared to control samples made without it and fired at the same temperature. In the bricks with ash there was a reduction in the phases detected in the control samples (quartz, phyllosilicates, and newly formed gehlenite, and diopside) and augite, a phase present in the volcanic ash, appeared. The volcanic ash fragments in the samples fired at over 950 °C turned red in color, owing to the formation of iron oxides. The increase in the concentration of volcanic ash caused a progressive increase in the vitreous phase and in clinopyroxene. Conversely, there were no significant differences in terms of their mineralogical composition between the fired bricks made with fine or coarse ash, although the samples with coarse volcanic ash apparently showed higher porosity.