Effects of chopped CFRP fiber on mechanical properties of concrete.

Enhancing concrete's mechanical properties has become a prominent field in recent years. Numerous studies investigated the possibility of enhancing the mechanical properties of concrete by adding additive materials. Few studies investigated the effects of copped CFRP on the tensile strength of normal-strength concrete (NSC) and low-strength concrete (LSC). In this study, the effects of Chopped Carbon Fiber Reinforced Polymer (CCFRP) on the mechanical properties of LSC and NSC were investigated. The method of the study was experimentally investigating the effects of CCFRP on the mechanical properties of LSC and NSC. Different volume fractions (0%, 0.25%, 0.5%, and 0.75%) of chopped carbon fibers were added to the concrete mix for the 13 MPa and 28 MPa concrete grades, and five mix trials were conducted to achieve concrete with 13 MPa and 28 MPa. The ratios (1:1.5:2.5) for the normal strength mix and (1:2.6:4.1) for the low strength mix were chosen. Three tests were conducted to evaluate the effects of chopped CFRP on the mechanical properties of concrete: compressive strength, tensile strength, and flexural strength. A total of 120 pieces were cast, including 24 beams, 48 cubes, and 48 cylinders. The casted cubes were 15 × 15 × 15 cm and the cylinders were 15 cm in diameter and 30 cm in length. Prism beams with a 15 × 15 cm cross-section and a 56 cm length were tested under a single point load. The samples were tested at 7 and 28 days of age, and the sample density was recorded. The results revealed that adding 0.25% CCFRP increased the compressive strength of LSC from 9.5 MPa to 11.2 MPa which is about 10% enhancement and slightly affected the compressive strength of NSC by about 5%. On the other hand, adding 0.25% CCFRP to both LSC and NSC increased split tensile strength from 2.5 MPa to 3.6 MPa which is about 44% enhancement for NSC and 16.6% for LSC. Similar improvements were made in flexural strength of normal strength increased from 4.5 MPa to 5.4 MPa. Whereas the effects on LSC were unremarkable. As such, this study recommends 0.25% CCFRP fiber as the ideal dosage.