Effect of Steel and Polypropylene Hybrid Fibers on Mechanical Properties of Recycled Aggregate M30 Concrete

This research focuses on studying the mechanical properties of recycled aggregate concrete (RAC) when hybrid fibers (steel and polypropylene) are added. Due to the increasing demand for natural aggregates and the growing problem of construction and demolition waste, recycled aggregates are seen as a sustainable alternative. However, RAC usually has lower strength because of the weak and porous nature of old mortar attached to the recycled aggregate. In this study, M30-grade concrete was prepared by replacing natural coarse aggregate with recycled coarse aggregate in proportions of 25% and 50%. Hybrid fibers were added in 1%, 2%, and 3% by volume. Concrete cubes, cylinders, and beams were cast and tested for compressive, split tensile, and flexural strength at 7, 14, and 28 days. The results showed that adding 2% hybrid fiber and 25% recycled aggregate gave the best strength results. The compressive strength reached close to 48.31 N/mm². Also, the split tensile and flexural strengths improved. This shows that hybrid fibers improve the performance of RAC and make it more suitable for structural use. This study supports the idea that recycled materials when used with fibers, can reduce waste and save natural resources.