The Use Of Slag, Tailings Autoclaved Brick

Steel slag is a solid waste produced in the process of steelmaking. Because of high content of f-CaO and f-MgO, volume expansion will occur when steel slag contacts with water, which greatly restricts its resource utilization. Stacking of steel slag will not only occupy land, but also result in severe environment pollution. Therefore, it is imperative to realize resource utilization of steel slag.First of all, In order to reduce costs and simplify treatment process stability, we made comprehensive analysis of steel slag properties and a lot of experiments. Modifier A(phosphate) and C(sodium carbonate and sodium hydroxide) were selected to improve the soundness of steel slag with the dosage of 1.2 % and 1.8 %(based the mass of steel slag) respectively. These two additives are can effectively improve the volume stability and activity of autoclaved brick from steel slag and tailings. Considering performance and cost, we chose modifier A for use in autoclaved brick.Secondly, we investigated the process conditions and curing regime of brick. The optimal conditions for producing autoclaved brick were obtained: ratio of water to solid 9 %; reaction temperature 140-180 ℃; forming pressure 20 MPa; autoclave time 2~4 h. The optimal material proportioning is: steel slag 25 %, cement 5 %, tailings 69.7 %, modifier 0.3 %. The autoclaved brick produced conforms to JC239-2001(fly ash brick) with the strength grade of Mu10.XRD and SEM were used to analyze hydration products and microstructure of brick in order to explore hydration-hardening mechanism of the autoclaved brick. The results showed that the main hydration products in this system are some gel materials like tobermorite, hydrate garnet and hydrated calcium aluminates. These hydration products contribute most for the mechanical strength of the autoclaved brick.In order to evaluate the durability of this product, we studied the freezing-thawing and drying shrinkage of autoclaved brick. It was showed that the loss of compressive strength and mass after freezing-thawing process, as well as drying shrinkage value, can all conform to JC239-2001(fly ash brick) with the strength grade of Mu10. Because of good durability, the products can be used for ordinary wall and load-bearing buildings.