Utilization of electric arc furnace oxidizing slag as concrete aggregate

Electric are furnace oxidizing slag (EF oxidizing slag) which is produced as a by-product from the steel-making process is utilized as concrete aggregates. Until now, the slag has hardly been used as concrete aggregates because of deterioration caused by the hydration of free lime and free magnesia included in the slag. In recent years, however, improvements in the electric steel making process have been carried out, and the possibility of applications of the slag has been increased. In this experiment, four types of EF oxidizing slag aggregates made in different cooling processes, i.e., air-granulated (rapidly cooled) slag, water-granulated (semi-rapidly cooled) slag, air-cooled (slowly cooled) slag, and improved slag (iron removed) are used. The chemical and mineralogical test results showed only a very small amount of f-CaO and f-MgO and did not detect unstable minerals. The durability of slag concrete was investigated by the measurement of length change. Air-granulated EF oxidizing slag aggregate concrete does not expand. Water-granulated and air-cooled EF oxidizing slag aggregate concretes expand slightly, but the increase in the expansion becomes flat after about 3 years. The expansion coefficient of the concrete stopped at about 0.03% or less. The strength and modulus of elasticity of the concrete were also investigated, and the results are discussed in comparison with concrete using natural rock aggregates. In the strength development of concrete, there is no significant difference between the slag aggregates and rock aggregates. The application of the slag aggregate as heavy weight concrete was carried out, and actual wave-dissipating concrete block and radiation shielding concrete were made. The results were good. The possibility of utilization of slag has been recognized, because satisfactory results were obtained in various tests for its use as a concrete aggregate.