AbstractIn this study, to evaluate the effects of using copper slag on the fresh and hardened properties of different cementitious composites, a total of 33 different mix designs were prepared for self-compacting lightweight concrete (SCLC), self-compacting concrete (SCC), and fiber-reinforced cementitious composite (FRCC). Replacing cement with silica fume and copper slag lowered the amount of cement consumption and improved the strength characteristics of concrete. By increasing the amount of copper slag from 0% to 30% of SCLC cement weight, the slump flow diameter increased by about 19% and d500 time decreased by about 37%. It should be noted that in SCC, like SCLC, increasing the copper slag level improved the workability of concrete. Adding copper slag up to 15% of cement weight increased the strength of SCLC up to 19%. Using 15% copper slag in the mix design increased the compressive, tensile, and flexural strengths of SCLC by about 17%, 19%, and 12%, respectively. Moreover, using 15% copper slag in SCC improved the compressive, tensile, and flexural strengths by about 21%, 25%, and 17%, respectively. The best-performing FRCC sample was found to be a hybrid sample containing 15% copper slag and 15% silica fume. In this case, the compressive, tensile, and flexural strengths of the FRCC increased by about 35%, 33%, and 28%, respectively. Therefore, in all three types of the mixes, increasing copper slag in the range of 15% to 20% of cement weight improved the mechanical properties of the specimens and more than that reduced it.