Effect Of Micro-powder Mixture Of Steel Slag And Granulated Blast Furnace Slag On Cement And Concrete Properties

Presently, China is a country with the largest crude steel output of 5 billion tons in the whole world. According to calculation, our country produces 1.5 billion tons blast furnace slag and 0.65 billion tons steel slag annually. How to utilize the metallurgical solid wastes is related to the economy development and circular economy level of our country.Based on the physical and chemical properties of steel slag and blast furnace slag, cement mortar experiments were conducted with different proportions of micro-powder mixture substituting for 50% cement. Effect of mechanical activation of the micro-powder mixture on the mortar activity index and fluidity ratio was investigated. Results showed that when equivalent substitution for cement occurred, the slurry water demand decreased with the increasing dosage of steel slag micro-powder in mixture. In addition, 28-day activity index of the micro-powder mixture decreased more significantly than 7-day activity index However, when steel slag micro-powder with different size fraction and a specific surface area ranging among 400～505m2/kg substituted for cement equivalently, no significant difference in water demand was found. In addition, the fluidity ratio of the micro-powder mixture increased slightly with the increasing of steel slag size.Three different kinds of active agents were used in this study to chemically activate the micro-powder mixture. Influences of the active agents on the activity index and fluidity ratio of the mixture were investigated. Results showed that the chemically activated mixture presented a much larger water content of pastes at standard consistency than the non-activated mixture. The alkaline active agent exhibited better activation effect on micro-powder mixture than the acidic active agent. However, the active agents contributed little to the enhancement of fluidity ratio of the mixture.Based on the cement mortar experiments, concrete experiments were performed using micro-powder mixture with different dosage and different steel slag micro-powder proportions to substitute for cement. Effect of micro-powder mixture on the concrete strength and durability was investigated. Results indicated that when concrete dosed 20%-80% micro-powder mixture was activated by KYH-10 active agent, its early compressive strength was increased significantly. Furthermore, the concrete exhibited good workability within the required slump range to meet the design strength requirement. Concrete mixed with large amounts of micro-powder mixture presented such good impermeability, drying shrinkage, frost resistance and resistance to chloride ion permeability that it can be used widely in concrete construction such as in ocean engineering.According to the laboratory studies, C30 concrete was prepared dosed micro-powder mixture with 60% steel slag to substitute for 50% cement and the concrete was used in industrial application test. Results showed that C30 concrete prepared by micro-powder mixture substituting for cement can meet the engineering construction requirements within the the required slump range.Moreover, the stabilization of steel slag was also studied. Especially, effect of steam and carbon dioxide on the content of f-CaO in steel slag was mainly investigated at different steel slag temperatures. Results indicated that the presence of liquid water was helpful to the reaction of f-CaO in steel slag. When steam and carbon dioxide were pumped in, the main reaction products were magnesium hydroxide, calcium hydroxide and calcium carbonate; however, when only steam was present but liquid water was absent, even if there existed carbon dioxide, it was difficult to produce calcium carbonate but magnesium hydroxide and calcium hydroxide.