Use of flint from phosphate mine waste rocks as an alternative aggregates for concrete

Abstract

Waste rocks resulting from phosphate mining extraction operations are characterized by a mix of lithological formations variety occurring within the phosphate sequence. Among this variety of co-products, flint is omnipresent in important quantities and considered as waste. This study investigates the feasibility of using flint as full aggregate replacement of natural gravel in concrete mixes. Several tests were carried out to determine their physical, chemical, mineralogical properties and mechanical performances according to European standard for concrete.Flint aggregates consist mainly of quartz and traces of dolomite and fluorapatite. Their geotechnical and physical properties are similar to natural aggregates used for concrete. Dry and wet abrasion values measured by Los Angeles and Micro-Deval tests are respectively 19 and 9.8. Flint-based concrete was prepared alongside a control concrete made of natural aggregates targeting a B25 concrete category (25 MPa), and it indicated an average of 29 MPa at 28 days versus 34.4 MPa at 28 days for the reference sample. Flint-based concrete has also indicated higher performances in terms of flexural strengths, reaching an average of 4.90 MPa. In addition, SEM microstructural characterization confirms that the Interfacial transition zone (ITZ) is stronger in the case of flint-based concrete compared to control concrete. Those performances mean that concrete based flint from phosphate mine waste rocks can successfully substitute the ordinary concrete in the civil engineering constructions, which will enhance the circular economy concept, and contribute as a solution to achieve a greener mining activity.