Engineering properties of controlled low strength material (CLSM) incorporating red mud

Abstract

Controlled low strength materials (CLSM), known as flow able fill is used as a replacement of compacted soil in cases where the application of the latter is difficult or impossible. The low mechanical requirements compared with concrete enable the use of industrial wastes for the production of CLSM. In general, CLSM mixtures consist of standard materials such as Portland cement, fly ash, fine aggregate and water. However, other industrial by-products and recycled materials are also accepted and encouraged as long as they are considered to be available, cost-effective for specific application and the necessary characteristics of the mixture such as flowability, strength, excavatability, and density are acceptable. The aim of this study is to evaluate the feasibility of incorporating red mud as a partial replacement for Portland cement into a controlled low-strength material (CLSM) made by industrial by-products (e.g., ponded ash and fly ash). A control mixture was initially produced with ponded ash, Portland cement, Class F fly ash, and water. For other mix proportions, red mud was substituted for Portland cement in amounts of 5, 10, 15, 20, 25, and 30 % by weight. The bleeding, flowability, fresh density, initial setting time of fresh CLSM mixtures were measured and the follows were hardened ones including compressive strength, corrosivity. Expectedly, all general properties of CLSM incorporating red mud did fall within the acceptable ranges. They performed well and conformed to the requirements of CLSM in ACI 229 standards with regard to flowability, bleeding rate, initial setting time, corrosivity and unconfined compressive strength. The partial replacement of cement by red mud, possibly up to 30 % in mixtures, would reduce flowability and slightly increase corrosivity evidenced by pH but still meet the requirements. Especially, it was found that an increase in red mud content could lead to an improvement in the stability (bleeding rate) and accelerate the setting process on the performances of the proposed CLSM. Finally, with regard to strength at 28 days, CLSM with highest strength could be produced by an optimum replacement of 15 % red mud to cement. In overall, it is worth noting that red mud could be feasible and potential in use as a partial replacement to Portland cement in CLSM production.