Resource utilization of solid waste from steel industries in cement-based cementitious materials: Mechanical properties, hydration behaviors, and environmental impact

With the increase in solid wastes from the steel industry, it is becoming increasingly important to increase the utilization of these. This study investigated the synergistic effect of granulated blast furnace slag (GBFS), steel slag (SS) and steel slag mud (SSM) in P.I Portland cement (PC) to improve their utilization. GBFS was used at three different levels (70%, 60% and 50%), and SS and SSM were both used at four different levels (10%, 20%, 30% and 40%). First, the physicochemical properties and activities of raw materials were analyzed. Second, the pozzolanic activity of ternary composite powder (TCP) was evaluated by isothermal calorimetry, X-ray diffraction and thermogravimetric analysis. Finally, TCPs were used as supplementary cementitious materials (SCMs), and their mechanical properties, hydration products, microstructure and environmental impacts were discussed. The results show that the addition of aluminate in SS retards the hydration of C3S in cement, and SSM almost does not affect the hydration of cement. In TCP system, the addition of SS and SSM promotes the formation of C-S-H and AFt at 3 d, but the C-S-H content in the specimens with high GBFS content is higher after curing for 28 d. When using TCP as SCMs, the content of GBFS should be ensured to be above 70%, a small amount of SS can improve the 3-d compressive strength of the specimens, and SSM needs to be added to avoid the aluminates in SS to delay the hydration of cement. The utilization rate of SS and SSM can be improved and the dependence on cement can be reduced to decrease CO2 emissions through the synergistic effect between GBFSSS-SSM without the addition of chemical additives, but the problem of heavy metal leaching remains to be resolved.