Effect of Fiber Type and Length on the Mechanical Properties of Recycled Aggregate Concrete

Substantial volumes of concrete waste are generated every day from construction and demolition activities, and this has become a global concern from an environmental perspective. Recycled aggregate generated as a by-product of construction and demolition waste can be used as an alternative to natural aggregates, which are being depleted in many countries, including Bangladesh. Although recycled aggregate has lower density, higher water absorption, and lower mechanical properties compared to natural aggregate, the incorporation of fiber in recycled aggregate mixes can improve the mechanical properties. This study investigates the physical and mechanical properties of recycled aggregate concrete reinforced with 0.51 mm diameter galvanized iron and 12 mm diameter polypropylene fibers. The test variables are fiber type and galvanized iron fiber length (15 mm, 26 mm, and 36 mm). Four different concrete mixes with 0.5% fiber content (by volume) are considered, along with one mix without fiber. Slump value, compressive strength, splitting tensile strength, flexural strength, and stress–strain behavior are analyzed and compared. The results indicate that the inclusion of fiber significantly reduces the workability of concrete. However, it enhances the mechanical properties of recycled aggregate concrete compared to the control concrete. Concrete mixtures containing galvanized iron fibers with lengths of 26 mm and 36 mm show the highest strength among the five mixes under study. However, concrete mixtures reinforced with shorter lengths of fibers are found to be more workable.