Influence Of Steel Slag And Composite Mineral Admixture Containing Steel Slag On The Properties Of Concrete

Steel slag is the by-product of steel-making. The discharge amount of steel slagis10%-15%of the steel output. The unused steel slag not only occupies the cultivatedland, but the heavy metal ions and the alkali metal ion it contains penetrate the soil,which results in water pollution. Thus, the study of the comprehensive utilization ofthe steel slag is of great importance.Steel slag contains some components (e.g. C3S and C2S) with hydraulicity, so ithas certain cementitious properties. Steel slag is a potential mineral admixture forconcrete. This thesis studied the soundness of the steel slag and the mechanicalproperties and durability of concrete with steel slag. The conclusions are reached asfollows.1) The soundness of different steel slag varies significantly. It is mainly becauseof the variety of different f-CaO content. The Ca(OH)2generated by f-CaO has alarger size or specific surface area than that produced by cement hydration, whichtends to lead to the expansion of concrete. Several elements contribute to whether thesoundness of steel slag would influence the micro-structure of steel slag, including theamount of the f-CaO in steel slag, the ratio of steel slag to complex binder and thestrength grade of the concrete.2) Under the condition of constant W/B, increasing the steel slag content tends todecrease many properties of the concrete. The negative effect of steel slag on theproperties of concrete is weaker at lower W/B. With the same compressive strength at28d, the early strength of the concrete with steel slag is weaker than the pure cementconcrete, but the later-strength is slightly stronger. The permeability, drying shrinkageand carbonation resistance of the concrete with steel slag is more or less the samewith the pure cement concrete.3) When the ratio of steel slag and ground granulated blast furnace slag (ggbs) is3:7, the fluidity, strength, elastic modulus of the concrete with steel and iron slag arevery similar to those of the concrete with ggbs. However, the concrete with steel andiron slag has a lower adiabatic temperature rise, smaller autogenous shrinkage anddrying shrinkage and better frost resistance ability. When the ratio of steel slag andggbs is4:6, the early strength and the strength at28d of the concrete with steel aniron slag is weaker than the concrete with ggbs. 4) A small amount of silica fume in the steel slag can greatly improve itsperformance, including the strength of the concrete and the permeability resistance tochloride ion. Steel slag with15%silica fume has similar properties to ggbs. Theinfluence of steel slag-super fine fly ash composite mineral admixture on the strengthof concrete is similar to that of ggbs. Though the concrete with steel slag-super finefly ash composite mineral admixture has a higher permeability than the concrete withggbs at28d, they have a similar permeability at90d.