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

Abstract

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.

Neutralization of Acidic Industrial Wastes and Fixation of Trace Element by Oil Shale Ash: Formation of a Green Product

“…As can be clearly seen in Figures – and compared to the SEM images of the untreated ash (see in the Supporting Information, Figure S1), the appearance and shape of the particles changed after the chemical treatment, probably, as a result of post-treatment dissolution of calcium minerals and other soluble minerals.…”

“…Their freshness and their degree of hardening were tested and compared. The mixing procedures as well as the freshness and hardening properties of the concrete were described by Nov et al 24 As was shown, the workability (slump) of the concrete containing untreated OSBA as a partial substitute was significantly reduced from 160 to 20 mm. However, the development of the compression strength was increased due to the pozzolanic reaction of OSBA with Ca(OH) 2 .…”

“…Treatment of OSBA. In a recent study, 24 it was found that treatment of OSBA with green acid (mixing the slurry of the solid OSBA in a solution of the acid for 15−20 min, filtering, and drying at room temperature overnight) via a ratio of 1:2.5 OSBA/green acid produces a treated upgraded version of OSBA. This treated OSBA is a product that is suitable to be used as a partial replacement for cement in concrete mixtures.…”

“…26 SEM Analysis. In addition, the SEM images in the treated OSBA in various OSBA/green acid ratios, compared to the non-treated OSBA 24 are presented in Figures 7−10, respectively.…”