Iron slag and copper slag are the residues of steel mills after smelting iron ore and copper ore. Fly ash is a ash powdery residue after the burning of raw coal. These so-called wastes have become "treasure" for cement plants.

Over the past decade, the cement and commercial concrete plants of South Cement Group have increased their use of these materials and developed a circular economy. The use of these secondary raw materials brings many benefits, because in addition to saving energy, reducing carbon dioxide emissions, and environmental protection, slag and fly ash are high-quality mixed materials for the production of special cements such as marine cement, cement for bridges, and tunnels. More importantly, these deeply processed blends are very cheap, with only half the price of cement. Therefore, it has become a very popular green energy-saving building material.