Evaluation on the effects of Cu(II) on the properties of blast furnace slag–cement composites with adding Cu-bearing solid wastes

• Cu(II) species (CuO, CuCl2, CuS) differentially affect the compressive strength and hydration of blast furnace slag–cement composites, with effects varying by grinding method and curing age. • At 3 days, CuO and CuS enhance strength of dry-ground composites but suppress wet-ground ones; at 28 days, the trend reverses, with all three species improving wet-ground composite strength. • CuCl2 reduces hydration degree in dry-ground composites but increases it in wet-ground ones; CuO promotes hydration in both, while CuS inhibits it. • Immobilization efficiency depends on composite type: dry-ground composites better immobilize CuCl2, while wet-ground composites better immobilize CuO and CuS due to finer particles and denser matrix.