| Steel slag is the inevitable product of the steelmaking process, and its generation amount is about 12% to 14% as steel production. Huge amount of steel slag is deposited, directly leading to environmental pollution and landfilled. In addition, it’s a great waste of resources. Steel slag contains cementitious minerals similar with Portland cement clinker as C3S and C2S. Thus it can be regarded as building material resources. However, the total amount of C3S and C2S is less than cement clinker and crystalline morphology is different, which leads to a worse cementitious activity than cement. There will be f-CaO in the slag without stabilizing treatment, resulting in poor volume stability. So the large-scale application of slag is restricted. In this paper, coke was used to reduce iron oxide in the steel slag to recover a part of iron. Then single modification materials were added to change the composition and crystalline structure. Thereby steel slag’s cementitious activity was improved and its application in the building materials industry is promoted. The utilization rate can be improved ultimately.In this paper, the convert slag of Tangshan Xinbaotai was selected as raw material, coke as reducing agent, lime as calcareous modification material and bauxite as aluminum modification material to remelt and modify the steel slag. The chemical and mineral composition were identified via chemical analysis, scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. Hydration process and products’microstructure characteristics of cement-based composite cementitious materials with slag after curing for 3d,7d,14d were researched via heat of hydration, differential thermal analysis, X-ray diffraction and scanning electron microscopy. Then the mechanical properties of cementitious materials were tested. Through exploring the influence of different types of modified material on slag composition in different dosage conditions, theoretical foundation and technical support were provided to realize industrialization experiment. The main results achieved in this paper are the following aspects:(1)30% cement is replaced by remelt slag to prepare mortar test blocks. The compressive strength increases by 20% to 40% after curing for 3d; 29% mostly increases after 7d; 100% can be reached after 28d. Hydration evolution of cement based composite cementitious materials can be promoted by steel slag. The hydration exothermic rate increases by 25% to 30%. The amount of chemically combined water is 9.20% more than cement after curing for 14d.(2)The cementitious properties of steel slag are improved to varying degrees with 1%,5%,10%,20% lime addition as calcareous modification material.3d,7d, 28d compressive strength of modified slag mixed with 5% lime increases by 62%, 42%,22% respectively, which has basically reached the performance of cement. Through the modification process above, slag’s hydration evolution is promoted at the same time. When the slag is modified with 5% lime, hydration heat for 168h is increased approximately by 63%.(3)Remelt and modify slag with bauxite. Slag’s hydration is promoted. The hydration rate of exothermic is significantly accelerated. The second exothermic peak appears 21h earlier than original slag and the peak reaches 2.75×10-3w/g, who is increased by 63%. Compared to original slag, the 3d,7d,28d compressive strength of modified slag with 1% bauxite is increased by 34%,23%,9% respectively.The experiments show that the slag modified with 5% coke and 5% lime has the best performance. The iron oxide content is decreased to less than 5%. The compressive strength of 3d,7d,28d are 28.8MPa,40.0MPa,52.5MPa respectively, which is basically reached the strength index of cement. |
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