Performance of Self-Compacting Concrete Containing Recycled Aggregates and Recycled Steel Fibers

Since the inception of self-compacting concrete, there has been a growing interest in integrating waste materials into its composition. This study explores the performance of self-compacting concrete and fibered self-compacting concrete, incorporating recycled aggregates sourced from the demolition and crushing of previously tested specimens. Additionally, it investigates the influence of steel fibers, both of commercial origin and those recycled from waste tires. The analysis spans both the fresh and hardened states, encompassing twelve concrete mixtures to assess workability (through measurements such as slump flow, T500, and L-BOX), segregation resistance, compressive strength, and flexural strength. Furthermore, the durability of these concrete mixtures is evaluated by examining mass loss and compressive strength after 56 days of exposure to acidic environments (HCl and H2SO4). The study is organized into three distinct series of concrete mixtures. The first series explores concrete without any fiber additives, focusing on replacing filler limestone with recycled concrete powder and/or substituting coarse aggregates with recycled concrete aggregates. In the second series, commercial fibers are introduced at a dosage of 30 kg/m³. The third series replaces the commercial fibers with recycled fibers with hooked ends. The assessment of the hardened state reveals enhanced mechanical properties in the case of fibered self-compacting concrete (compressive strength increased by more than 9%, and flexural strength increased by more than 8%). Notably, the results highlight that recycled aggregates exhibit improved resistance to HCl acid attack. Interestingly, the replacement of commercial fibers with recycled fibers does not substantially affect the concrete's resistance to acid exposure.