Influence of Steel Slag Aggregate Gradation on the Improvement of Concrete Properties

Steel slag, as a by-product of the iron industry, is widely produced in the world. In this paper, steel slag from local furnaces is partially replaced as concrete aggregate to compensate for irregular consumption of raw material for concrete and reduce environmental impacts of waste slag. Six mix designs were considered, and three categories of aggregate size were selected to evaluate the aggregate replacement effect in the concrete samples. Sieve analysis, X-ray diffraction (XRD) analysis, aggregate porosity, slump, compressive strength, and microstructure analysis were implemented to investigate aggregates and concrete samples. The results showed that compressive strength and water absorption of the concrete with 20% aggregate replacement were 37.4 MPa and 3%. By 20% aggregate replacement, improvement in the compressive strength and reduction in the water absorption were observed. Increasing aggregate replacement to 40% reduced compressive strength by 62% and increased water absorption. In the concrete containing 62% of the replacement, the required compressive strength of 30 MPa, as design compressive strength, was achieved. However, although the pores in the slag aggregates can affect fresh and hardened properties of concrete, selecting an appropriate range of aggregates from the gradation curve can limit the side effects due to the pores.