Experimental research on the properties of foamed mixture lightweight soil with red mud

Red mud (RM) is a kind of alkaline waste produced by the extraction of alumina from bauxite. According to statistics, approximately 1.5 billion tons of RM are produced worldwide annually. The existing storage methods of RM not only occupy a large number of land resources but also damage to environment owing to the presence of highly alkaline and trace heavy metal elements. This study converted wasted RM into foamed mixture lightweight soil (FMLS), a type of eco-friendly material primarily made of foam and cement. Investigations were done into the flowability, unconfined compressive strength (UCS), durability, and microstructure of FMLS with RM (FMLSR). 10 %, 15 %, 20 %, 25 %, and 30 % substitution percentages (by weight) of RM for cement were taken into consideration. The results show that the compressive strength of FMLSR was greatest when the RM replacement percentage was 20 %, and the water stability coefficient of FMLSR was greater than 0.7 when the RM replacement percentage was less than 25 %. Although the FMLSR cured for 28d generated more C-S-H gels and had a better microstructure when the replacement percentage of RM was 20 %, the UCS was still lower than that of FMLS without RM due to the relatively low Ca/Si ratio of the generated C-S-H gels. The utilization of RM not only consumes large amounts of waste and reduces environmental pollution but also frees up many land resources and reduces carbon emissions.