Resource Utilization of Limestone Powder and Steel Slag Powder in Cement-Based Materials at Extremely Low Water/Binder Ratio.

The large-scale resource utilization of limestone powder generated from mining operations and steel slag waste discharged from the metallurgical industry is of vital importance. The effects of limestone powder or steel slag powder on the properties of cement-based materials at an extremely low water/binder (w/b) ratio of 0.16 under standard curing and early high-temperature curing at 60 °C for 3 d were comparatively studied through measuring the compressive strength, hydration degree and microstructure. The results show that limestone powder promotes the early strength development of concrete at an extremely low w/b ratio better than steel slag powder does under standard curing conditions, but steel slag powder promotes the late strength growth better. For concrete containing 10% and 20% steel slag powder, the compressive strength increased by 20.4 and 33.7 MPa, respectively, from 3 to 7 d, and the difference in their compressive strengths was only 0.4 MPa at 90 d. The limestone powder promotes strength more significantly under early high-temperature curing conditions; however, when the dosage reaches 30%, the long-term strength of the concrete containing steel slag powder is marginally greater compared to the concrete containing limestone powder. At 90 d under early high-temperature curing, the chemically bound water contents of the pastes containing limestone powder ranged from 9.05% to 10.53%, compared with 10.64% to 11.85% for the pastes containing steel slag powder. The diffraction peak intensity of ettringite is stronger in the paste with limestone powder due to the stabilizing effect of limestone powder on ettringite. The diffraction peak intensity of Ca(OH)2 is stronger in the paste with steel slag powder, which exhibits a higher hydration degree and generates more hydration products. The pore structure of the sample containing steel slag powder improves, and the microstructure becomes denser at high temperatures.