Copper slag (CS) was considered a major by-product produced from the copper refining industry, which estimates about 2.2 to 3 tons generated during the production of every one ton of copper. At the same time, continuous dumping and improper disposal of this byproduct have led to serious environmental problems, especially due to the leaching of heavy metals into soil and water. This review carefully studies the potential of CS as a sustainable construction material through a clear distinction of its performance, especially when used as a fine aggregate and as a supplementary cementitious material (SCM). Due to the presence of higher content of iron and silica, higher hardness, and very low water absorption, it was found that CS helps in improving the density and durability of concrete. When used as a fine aggregate, CS enhances workability, strength, and durability at an optimum level of about 40%, mainly due to better particle packing and reduced pore connectivity. On the other hand, when used as an SCM, CS contributes to long-term strength through pozzolanic reactions and the formation of C–S–H gel, but its replacement level should be limited to about 20% to avoid loss of early-age strength caused by reduced alkalinity. In terms of durability, the use of CS can reduce water absorption by up to 60%, lower chloride penetration, and improve resistance to sulfate attack. Environmental Life Cycle Assessment studies show that CS can reduce global warming potential by about 12–19% and also decrease overall energy consumption. Statistical validation using multi-criteria decision analysis (MCDA) and separate regression modeling with an R2 value of about 0.965, which supports these optimum replacement levels up to 40% for fine aggregate and 20% for cement, providing a good balance between strength, durability, environmental benefits, and cost. Overall, this review shows that CS is a valuable and multi-functional material that supports circular economy practices when used with a proper mix design based on specific applications.
Vijayan et al. (Wed,) studied this question.