Performance Evaluation of Recycled Aggregate Concrete Enhanced with Hooked Steel Fibers: Fresh and Hardened Properties

Natural aggregates are finite, and the volume of demolished concrete waste makes recycling an essential alternative to be explored. RCA has been a recognized concept for a long time, but the strength losses associated with it have discouraged its widespread adoption. Therefore, this research aimed to investigate whether adding steel fibers to the mix would be sufficient to address this limitation. Four different RCA levels (0%, 25%, 50%, and 75% replacement) were applied. Fibers were introduced at various levels up to 1.0%. The fresh concrete was evaluated using the slump test, and the samples were examined for compressive, flexural, and splitting tensile strengths at the age of 28 days. The results clearly indicate reduced strength with increasing RCA content, which is an expected outcome. The aggregate is porous, and the bond with the cement paste is relatively weak; hence, the reduction in measured values. The effect of fiber incorporation was more pronounced. At 25% and 50% RCA, a fiber content in the range of 0.4 to 0.6% was sufficient. However, at 75%, it is necessary to increase the fiber content to 1.0% to obtain acceptable tensile and flexural values. Increased fiber content slightly reduced workability, but to a limited extent, as admixtures effectively compensated for this effect. RCA is not ideal; however, the evidence presented suggests it does not necessarily constitute a limiting factor. It is essential to carefully control the fiber dosage. Insufficient fiber content results in reduced strength, whereas excessive fiber content renders the mixture difficult to handle. In fact, matching the fiber dosage to the amount of RCA used may provide structurally sound concrete. This is an important consideration for projects where the reduction of virgin material consumption is required.