Treated Oil Shale Ashes as a Substitute for Natural Aggregates, Sand, and Cement in Concrete

Oil shales are rocks that contain organic matter and are used as a low-grade fuel for energy production. The oil shale combustion process produces large quantities of ash as combustion wastes. These residues contain a high concentration of calcium anhydrite (CaSO₄) and calcium carbonate (CaCO₃), which can be utilized to neutralize acidic wastes (e. g., wastes from the phosphate industry).Using untreated oil shale bottom ash as partial substitutes for aggregates, natural sand, and cement in concrete mixtures has resulted in a significantly decreased performance of the concrete mixtures. However, by blending the oil shale with acidic materials, the concrete properties improved, as manifested by the development of compressive strength and the workability of the concrete mixtures. In the current study, it was shown that treatment of the oil shale ash with the acidic waste of the Israeli phosphate industry or with phosphoric acid significantly improves the properties of the concrete mixtures, by partial replacement of the natural aggregates and sand by the treated oil shale ash.