Mechanical and microstructural properties of cement-treated marine dredged clay with red mud and phosphogypsum: Fid-Bau Portal

Mechanical and microstructural properties of cement-treated marine dredged clay with red mud and phosphogypsum

Wan, Xing / Ding, Jianwen / Jiao, Ning / Mou, Cong / Gao, Mengying

Abstract Cement-based solidification technology is an ideal solution to convert undesirable marine dredged clay (MDC) to qualified filling materials. Industrial by-products (e.g., fly ash) are commonly added as partial replacement of cement, aiming to reduce carbon emissions and relieve severe stockpiles of industrial wastes. Red mud (RM) and phosphogypsum (PG) are increasingly generated and dumped in China, but have an extremely low utilization rate among various by-products. Potential use of the combined RM with PG in improving cement-treated MDC is experimentally investigated in this paper. A series of laboratory tests, including unconfined compressive strength (UCS) tests, hydraulic conductivity tests, microscopic tests, were carried out. The influence of RM/PG ratio, initial water content and cement content on mechanical and microscopic properties was examined, respectively. The results indicate that the role of 5% RM combined with 5% PG (by dry weight of soils) in improving strength approaches that of 5% additional cement. As cement content reaches 20%, the hydraulic conductivity of stabilized MDC decreases below 1 × $ 10^{–8} $ cm/s with optimum content of wastes. The stabilized MDC with combined RM and PG has a denser microstructure due to mutual promotion between RM and PG. The sulfate ions provided by PG help to break bonds of Si–O and Al-O in the RM and MDC with an alkaline environment, generating more C-S–H, C-A-H and C-A-S–H. The produced C-AH contributes to the formation of ettringite with sulfate ions released from the PG in turn. The combined RM with PG shows promising application in cement-based solidification of MDC.