Abstract
The road construction sector is a worldwide high consumer of natural aggregates. The use of unusual industrial by-products in road techniques can contribute to the conservation of non-renewable natural resources and the reduction of wastes produced by some industries. Phosphate waste rocks could be considered as potential alternative secondary raw materials in road construction. The use and valorization of these wastes is currently limited according to the Moroccan guide for road earthworks (GMTR). The guide has classified these materials as waste products, which consequently, cannot be used in road construction. However, phosphate waste rocks are sedimentary natural rocks which have not been subjected to any transformation other than mechanical fragmentation. The goal of this paper is to discuss key-properties of various phosphate mine waste rocks (PMWR) to be used as road materials. Samples were taken from different stockpiles in the phosphate mine site of Gantour in Morocco. The different waste rocks samples were characterized in terms of their physical, geotechnical, chemical, mineralogical and environmental properties using international testing norms. The obtained results showed that the studied PMWR presented satisfying characteristics; the specific (particle) density: ρs > 26 kN/m3, Los Angeles abrasion: 45% < LA < 58%), methylene blue value MBV < 1 g/100g, organic matter: OM < 1% and plasticity index: PI < 20%. All PMWR were confirmed as possessing the requested geotechnical properties to be used as materials for embankments. Moreover, leaching tests showed that none of them released any contaminants. In field application, these materials have been also successfully used in in situ experimental pilot testing. Therefore, the PMWR have to be classified in the category of natural aggregates that are similar to conventional materials.
Highlights
Various stakeholders in the road construction sector have to deal with the increased demand of raw materials used in road infrastructures
The aim of this paper is to focus on phosphate mine waste rocks (PMWR) and its use in the construction of road embankments and to discuss their status in Moroccan Guide for Road Earthworks
The results showed that the maximum dry density corresponding to 19.5 kN/m3 was recorded for the compaction energy of four passes, the reference dry density is taken equal to 19.5kN/m3 .The calculation of the compaction rates makes it possible to show that the application of a compaction energy of two passes does not satisfy the required compaction levels for embankments contrary to four and eight passes (Table 5)
Summary
Various stakeholders in the road construction sector have to deal with the increased demand of raw materials used in road infrastructures. An increasing attention has been given to the potential use of alternative aggregates, in the road construction sector [1]. Several factors must be considered before using a waste or by-product in road engineering. The use of industrial wastes as secondary and alternative materials in the infrastructure sector depends on their availability, on the transport costs and their physical, geotechnical and chemical properties. The use of alternative materials in road construction provides several economic and ecological advantages. When waste materials with acceptable properties are available, it is possible to avoid the costs related to the extraction, and to minimize the transport distance, energy consumption and the greenhouse gas emissions [3]
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