Valorization of phosphate mine waste rocks as aggregates for concrete A. El Machi a,⇑ , S. Mabroum a,b , Y. Taha b , A. Tagnit-Hamou c , M. Benzaazoua b,d , R. Hakkou a,b a Cadi Ayyad University (UCA), Faculty of Science and Technology, IMED-Lab, BP549 Av. A. El Khattabi, Marrakech 40000, Morocco b Mohammed VI Polytechnic University (UM6P), Mining Environment & Circular Economy (EMEC) Program, Ben Guerir 43150, Morocco c Université de Sherbrooke, département de génie civil, Sherbrooke, Canada d Institut de recherche en mines et environnement (IRME) UQAT, Rouyn-Noranda, Canada article info Article history: Received 28 June 2020 Received in revised form 23 July 2020 Accepted 14 August 2020 Available online xxxx Keywords: Phosphate waste rocks Valorization Construction aggregates, concrete Circular economy abstract The phosphate industry produces great amounts of waste-rocks during their mining activities in extrac- tion and beneficiation steps. Waste-rocks are stored immediately on extraction sites or in the vicinity of treatment facilities. Different types of waste-rocks are generated, yet this paper discusses the use of stone-removal waste-rocks as aggregates for concrete. Starting from the chemical and mineralogical composition, those waste-rocks were characterized by different techniques. Common geotechnical tests were performed to assess the aggregates properties. Then, those aggregates were used in concrete formu- lation as a full replacement of natural aggregates in order to test their mechanical behavior in comparison to a reference concrete, using compressive, flexural and splitting tensile strengths as parameters to eval- uate the concrete performance according to the required standards. Those aggregates indicated a 41% Los Angeles coefficient, 43% Micro Deval coefficient and 5.20% Water Absorption coefficient. The WRAM concrete has indicated an average of 12 MPa of compressive strength, 1.3 MPa of flexural strength and 2.65 MPa of splitting tensile strength at 28 days. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of The International Confer- ence on Water Depollution and Green Energy 2019. 1. Introduction The development of infrastructures and civil engineering con- tinue to increase every year making concrete the most used con- struction material in the world compared to steel, wood, plastics and aluminium [1]. Every year, the use of concrete is estimated >11 billion metric tons [2]. Coarse aggregates occupied 60%–80% of concrete volume, playing a crucial role in the development of concrete mechanical properties [3–5]. Beshr et al. stated that fail- ure planes of high resistant concrete cross the coarse aggregates, confirming that compressive and splitting tensile strengths were deeply affected by the nature of these aggregate [6]. The demand of aggregates for concrete industry is continuously increasing lead- ing to the depletion of natural resources. To reduce the dependence on natural aggregates, much researchers studied the substitution of natural aggregates by industrial by-products as an alternative way for the construction industry [7-15]. Large quantities of waste rocks, generated during the open pit mining of the Moroccan phosphate mines, are considered as solid wastes and deposited without sorting in stockpiles in the vicinity of mine sites [16]. These waste rocks represent mainly the interca- lation layers which host the phosphate-rich layers and the over- burden; they are characterized by a mix of wide variety of lithological formations. Phosphate waste rocks are confirmed to have never undergo any chemical treatment; and it is proven that they don’t pollute surface or underground water, but they reduce arable lands, modify topography and disfigure landscapes [17]. Therefore, it should be considered as natural resource of aggregate, and to enhance the idea of aggregates from Moroccan phosphate mines are co-products and not waste rocks. Many solutions have been sought for this major issue in phos- phate mining, and the recycling as construction material is the most interesting option to be investigated. Clays composed of paly- gorskite phase as a clayey mineral from phosphate rocks were used to elaborate fired bricks, revealing that a pressure of 5 MPa and heating temperature at 1050 °C for 2.5 h allowed the maximum mechanical characteristics [16]. While, clays containing montmo- rillonite mineral could successfully be used as an aluminosilicate precursor to synthesize geopolymers materials with a compressive strength of 25 MPa for curing at ambient temperature [18]. In addi- tion, phosphate waste rocks showed promising geotechnical prop- erties as material for road constructions [19]. https://doi.org/10.1016/j.matpr.2020.08.404 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of The International Conference on Water Depollution and Green Energy 2019. ⇑ Corresponding author. E-mail address: aiman.elmachi@ced.uca.ma (A. El Machi). Materials Today: Proceedings xxx (xxxx) xxx Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr Please cite this article as: A. El Machi, S. Mabroum, Y. Taha et al., Valorization of phosphate mine waste rocks as aggregates for concrete, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.08.404