Improvement of engineering properties of pond ash based CLSM with cementless binder and artificial aggregates made of bauxite residue

Background Controlled low strength material (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. Methods A study was conducted to investigate the feasibility of newly developed controlled low strength material (CLSM) using industrial wastes (pond ash, artificial aggregate made by red mud) and cementless binder as a full substitute of Portland cement in mixtures. The compressive strength of pond ash based CLSM binded with Portland cement meets in the desirable range of excavatable CLSM while pond ash based CLSM binded with cementless binder, which fully replaces the cement, shows slightly lower strength than excavatable CLSM strength ranges. In order to improve engineering properties of pond ash based CLSM binded with cementless binder, artificial aggregate that was made of Bauxite residues, red mud, was mixed with pond ash. Several mixtures made with binders and aggregates were systematically tested to determine the engineering properties of controlled low strength material such as flow consistency, compressive strength and thermal conductivity. Results Expectedly, particle size distribution analysis result of pond ash was transformed from poorly graded sand to well graded sand mixture in USCS. After the combination of pond ash with artificial aggregate, the engineering properties of CLSM were improved. Conclusion A compressive strength of pond ash-artificial aggregate mixture is remarkably increased and meets the requirement of excavatable CLSM of ACI even though binded with cementless binder. Furthermore, flow consistency of all CLSM mixtures has reached highly flowable range of 200 ~ 300 mm conformed by the American Concrete Institute (ACI 229R). In addition, a significant point for flow consistency is that cementless binder can be a good component material to control the segregation separation of constituents in proposed mixtures. For the purpose of the use of proposed CLSM as a backfill material for underground boreholes and pipes, a thermal conductivity was also measured. Sufficiently high values (over 0.8W/mK) of thermal conductivity found demonstrate that the proposed mixtures are appropriate to the practical application of backfill materials for underground boreholes and pipes.