The Effect of 30% Steel Slag Utilization and the Addition of Shredded PET (Polyethylene Terephthalate) Plastic on the Shear-Flexural Capacity of Reinforced Concrete Beams with Minimum Reinforcement Ratio

Abstract

This study aims to evaluate the effect of using steel slag (SS) as a 30% fine aggregate substitution and adding shredded Polyethylene Terephthalate (PET) at levels of 0%, 0.4%, and 0.6% on the shear–flexural capacity of reinforced concrete beams with a minimum reinforcement ratio. An experimental laboratory method was employed using reinforced concrete beam specimens measuring 5 × 10 × 110 cm and cylindrical specimens for compressive strength testing. Concrete mix design followed SNI 03-2834-2000 with a target compressive strength of 22.5 MPa. The test results indicate that a 30% steel slag substitution reduced the compressive strength compared to normal concrete; however, the addition of shredded PET improved the mechanical performance and structural capacity of the beams. The optimum performance was obtained with the combination of 30% steel slag and 0.4% PET, which produced the highest shear–flexural capacity and ultimate load among all variations. Increasing the PET content to 0.6% did not consistently enhance beam capacity and, in some cases, resulted in performance reduction due to decreased mix homogeneity. The observed crack patterns showed initial flexural cracking in the tension zone, followed by the development of diagonal tension cracks as a continuation of flexural cracks, leading to sudden shear–flexural failure. This failure mechanism is consistent with the behavior of reinforced concrete beams described by Nawy (2009) and Wang and Salmon (1993). The results demonstrate that steel slag and shredded PET have strong potential as environmentally friendly alternative materials for reinforced concrete beams.