Effects of adding slags on strength and leaching properties of soft soil

Dredged soils are typically mixed with additives to improve their mechanical properties and reduce the risks of leaching toxic elements. An evaluation of blast furnace slag and steelmaking slag as additives is presented here. For this study, Kasaoka clay was used to simulate soft soil. It was mixed with 10, 30, or 50% of slag and cured for several days. Each soil–slag mixture contained only one type of slag. Unconfined compression strength tests were conducted to discuss the soil’s strength characteristics. Batch tests were used to evaluate the leaching behavior of laboratory-prepared arsenic-contaminated soils. Steelmaking slag had a discernible impact on the soil’s strength, but blast furnace slag had no significant effect. When more steelmaking slag was added to the soil, and the mixture cured for longer periods, the soil’s strength dramatically increased. A 28-day cured soil–slag mixture containing 50% slag had a strength of ~ 250 kPa. The contaminated soil leached 1.9 mg/L of arsenic without adding slag. When it was mixed with blast furnace slag and steelmaking slag, the leaching concentrations were < 1.0 and < 0.02 mg/L, respectively. The soil complied with Japan’s 0.01 mg/L leaching limit for contaminated soils after adding 30% or more of steelmaking slag.