Mechanical properties of steel-polypropylene fiber reinforced fully recycled coarse aggregate concrete

In this study, the steel fiber and the polypropylene fiber were used to enhance the mechanical properties of fully recycled coarse aggregate concrete. Natural crushed stone was replaced with recycled coarse aggregate at 100% by volume. The steel fiber and polypropylene fiber were used as additive material by incorporating into the mixture. In this test two parameters were considered: (a) steel fiber volume ratio (i.e., 0%, 1%, 1.5%, 2%), (b) polypropylene fiber volume ratio (i.e., 0%, 0.1%, 0.15%, 0.2%). The results showed that compared with no fiber, the integrity of cubes or cylinders mixed with fibers after failure was better. When the volume ratio of steel fiber was 1 similar to 2%, the width of mid-span crack after flexural failure was 5 similar to 8 mm. In addition, when the volume ratio of polypropylene fiber was 0.15%, with the increase of steel fiber content, the static elastic modulus and toughness of axial compression first increased and then decreased, and the flexural strength increased, with a range of 6.5%similar to 20.3%. Besides, when the volume ratio of steel fiber was 1.5%, with the increase of polypropylene fiber content, the static elastic modulus decreased, with a range of 7.0%similar to 10.5%. The ratio of axial compression toughness first increased and then decreased, with a range of 2.2%similar to 8.7%. The flexural strength decreased, with a range of 2.7%similar to 12.6%. On the other hand, the calculation formula of static elastic modulus and cube compressive strength of fully recycled coarse aggregate with steel -polypropylene fiber was fitted, and the optimal fiber content within the scope of the test were put forward.