Composite fibers in concretes with various strengths

Abstract

Concrete beams reinforced by short composite macrofibers uniformly distributed in their volume were tested mechanically in bending. The short composite macrofibers were a few centimeters long and less than 2.5 mm (0.01 in.) in diameter. Macrofibers were manufactured impregnating glass or carbon-fiber tows by epoxy resin, forming unidirectionally oriented composite material rods later cut in short pieces. Such fibers were designated in the framework of the paper as macrofibers. The length-to-diameter ratios L/d of the glass and carbon macrofibers were equal to 22.9 and 28.2, respectively. The beams were loaded until the opening of the macrocrack reached 5 mm (0.02 in.). The macrofibers bridging the crack were pulled out during opening of the crack. Low-, medium-, and high-strength concretes in the range of 40 to 120 MPa (5800 to 17,405 psi) were used in the experiments. Pullout tests with single fibers were carried out. The volume fraction of the fibers in concrete was 1.5%. Two types of fiber-reinforced concrete beams with glass and carbon fibers were manufactured and tested, and the data obtained were compared with experimental results for steel fiber-reinforced concrete beams. The potential of the composite fibers was analyzed.