Waste and industrial by-products represent a significant percentage of the industrial landfill. The evaluation of these products has a dual effect: it avoids both the landfill (risk of environmental pollution) and limits the use of natural aggregates (depletion of natural resources and landscape fragmentation and the imbalance of the ecosystem). In recent years, applications for industrial waste have been taken into account in the construction of roads with a great interest in many industrialized countries and developing countries. The use of these materials in the construction of the road is a decision based on technical, economic and ecological criteria. In Algeria, the steel plant of El-Hadjar (Annaba), due to its activity generates a significant industrial waste (slag) which creates a storage problem and pollution. For industrialized countries, this product is an abundant raw material at low cost that must be used on a large scale public works. Our study implies the use of slag in the preparation of the subgrade and surface course (as coated). The results of chemical, physical and mechanical analyses of El-Hadjar slag and materials developed, compared to those of natural aggregates, can be used as aggregate in road construction.