Effects of recycled scrap alumina on the physical and mechanical properties of calcium sulfo-aluminate cement products

This work aims to resolve the environmental problem caused by alumina scrap by studying the effects of its partial replacement on physical and mechanical properties of calcium sulfo-aluminate (CSA) cement products. To this effect, mixtures obtained from a partial replacement of bauxite with respectively 0, 10, 20, 30 and 40% of recycled alumina scrap were studied. After processing the various raw materials (bauxite, limestone and alumina scrap), they were mixed together, pressed at 2 MPa and heated at 1200 °C. The resulting clinkers were crushed and mixed with 15% of commercial gypsum to obtain the various CSA cement powders used to produce testing specimens. The raw materials as well as the synthesized products were characterized. Globally, it appears that the addition of 30% of alumina scrap enhances both physical and mechanical properties of CSA cement products. After 28 days, CSA cement products obtained with the addition of 30% of alumina scrap show a densified structure with the lowest porosity and the highest compressive strength (40 MPa) as compared to those obtained without addition. Also, the addition of 30% of alumina scrap enables to obtain CSA cement products endowed with short setting time (3 to 8 min) and containing greater amount of ye’elimite (54.54%) as compared to those obtained without addition (45.34%). Indeed, alumina scrap promotes the formation of ye’elimite which is progressively transformed into ettringite with curing time and thereby contributing for the hardening of specimens. Hence, the recycling and using of alumina scrap in certain amount (30%) to substitute bauxite during the synthesis of CSA cements, is a suitable process to obtain sustainable binders endowed with improved physical and mechanical properties. These CSA cements can be technologically used to produce mortars and concretes for the construction of bridges and other related civil engineering applications. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.