Assessing the Suitability of Phosphate Waste Rock as a Construction Aggregate

Abstract

Phosphate waste rock (PWR) is gaining attention as a potential alternative aggregate for concrete. Its valorization could reduce the environmental impacts of quarrying natural resources and stockpiling phosphate mining waste. This study comprehensively investigated the properties of fine and coarse aggregates produced from three rock types selected from PWR in Morocco: Flint, Phosflint, and Dolomite. A range of techniques was used to study their characteristics, including microstructural observations up to the microscale and X-ray computed tomography (X-CT), mineralogical and chemical compositions, physical and geotechnical properties such as Los Angeles (LA), micro-Deval (MDE), flexural strength, real dry density, and total porosity. The results showed that the coarse fractions of Flint, Phosflint, and Dolomite are code A or B of NF P 18-545 and exhibit good shape, density, and water absorption properties. Flint aggregates had the highest wear and fragmentation resistance with the lowest and finest porosity. They contained mainly quartz but also small proportions of Dolomite and fluorapatite. Phosflint aggregates had high resistance, shown by code A in LA and MDE values, and flexural strength equal to 17.1 MPa. They contained phosphate microfacies with a Ca/P atomic ratio equal to 1.8, cemented by cryptocrystalline silica. Dolomite aggregates’ mineralogical make-up consisted mainly of dolomite with the presence of quartz particles in addition to impurities. They also displayed significant total porosity (10–12%), as confirmed by X-CT. These findings were discussed to develop insights for the use of three types of PWR as alternative aggregates for concrete production. This investigation contributes to unveiling the properties of PWR as concrete aggregates and encourages circularity between the mining and construction sectors.