Production of asphalt mixes with copper industry wastes: Use of copper slag as raw material replacement

Abstract

Copper slag is a waste obtained from copper production and it has a limited use, being mainly accumulated in landfills on a massive scale. This material presents a high hardness and it has hydrophobic properties, so it can be used as aggregate replacement in the production of asphalt mixtures. However, each size of copper slag behaves differently when used in asphalt mixes, especially under changing conditions of moisture or temperature. Precisely these climatic factors directly affect the service life of asphalt pavements. In this research, semi-dense graded asphalt mixtures were produced with copper slag as replacement of aggregates, varying the particle sizes used in the range from 2.5 to 0.08 mm to determine the size of copper slag with the best performance. Indirect tensile strength tests were used to analyze samples subjected to different moisture and temperature conditions and ageing degrees. The results show that copper slag can be used as aggregate replacement in asphalt mixes when the proper size is selected. The strength of the asphalt mixture increased as the size of the copper slag increased, especially under variable moisture and ageing conditions. Superior behaviour compared to a reference mixture was obtained when replacing the size of aggregate No. 8 with copper slag, increasing its indirect tensile strength and retained strength, reducing its stiffness under all the ageing periods, and being equally effective at the different temperatures, which results in mixtures with improved durability and delayed cracking. Furthermore, it would help to reduce between 15 and 20% of the virgin aggregate needed to produce asphalt mixes and it would also allow reducing the accumulated volume of this waste, decreasing the environmental impact of both industries.