Using alum sludge for clay brick: an Irish investigation

Abstract

Throughout the world, alum sludge is dewatered and the resultant cakes are discarded in landfill. This paper reports a study to investigate the possible incorporation of alum sludge as a partial replacement for clay in clay brick manufacturing. It is the first study of this problem in Ireland. Alum sludge cakes and clay were separately dried, ground and sieved in preparation for making test specimens. Cylindrical clay bricks were made at different temperatures (800, 1000, 1100, 1200 °C), incorporating different percentages (0, 5, 10, 15, 20, 30, 40% by dry weight) of alum sludge. The bricks were then subjected to compressive strength test and submersion. Loss on ignition, water absorption and weight reduction were calculated. It was found that bricks containing up to 20% sludge, fired at 1200 °C, or containing 5% sludge and fired at 1100 °C have met the European and Irish Standards as set out by Eurocode 6 – ‘Design of Masonry Structures’. The firing temperature and the increase in sludge content affected the final clay-sludge brick colour. By increasing the proportion of alum sludge, compressive strength decreased and the final weight of the brick was reduced. Firing temperatures that are too high may result in damage to the bricks during firing. This study has demonstrated the promising potential and prospects for Irish dewatered alum sludge cakes in clay-sludge brick making.