Fire resistance performance of clinker-free cementitious materials produced from phosphorus slag, calcium carbide slag, desulfurization gypsum, and metakaolin

The large-scale accumulation of phosphorus slag not only occupies land but also pollutes the environment. Converting phosphorus slag into building materials is an effective way to achieve its recycling. Studies have shown that utilizing calcium carbide slag and desulfurization gypsum to synergistically activate phosphorus slag, while adding metakaolin to provide additional alumina for the cementitious system, can successfully produce clinker-free cementitious materials with good performance. However, before the clinker-free cementitious materials can be applied in practical engineering, their high-temperature mechanical properties need to be evaluated to ensure that their fire resistance meets the requirements. This study investigates the effects of high temperatures on phosphorus slag-based clinker-free cementitious materials, including four systems: the binary system of phosphorus slag and calcium carbide slag, the ternary system of phosphorus slag, calcium carbide slag, and desulfurization gypsum, the ternary system of phosphorus slag, calcium carbide slag, and metakaolin, and the quaternary system of phosphorus slag, calcium carbide slag, desulfurization gypsum, and metakaolin. After being exposed to high temperatures of 200 ℃, 400 ℃, 600 ℃, and 800 ℃, the compressive stress-strain relationships of different samples were tested. The changes in hydration products were analyzed using techniques such as X-ray diffraction, Fourier-transform infrared spectroscopy, and thermal gravimetric. The results show that after exposure to temperatures above 400 ℃, the mechanical properties of the phosphorus slag-calcium carbide slag binary system deteriorate rapidly, and surface cracking occurs. By simultaneously incorporating an appropriate amount of desulfurization gypsum and metakaolin to the phosphorus slag-calcium carbide slag binary system, not only can the mechanical properties at room temperature be significantly improved, but their fire resistance at temperatures above 400 ℃ can also be effectively enhanced. Overall, the quaternary clinker-free cementitious material has promising application prospects.