Microstructure of the carbon and the polypropylene hybrid fiber reinforced concrete acted by bending and tensile stress

Specimens of carbon and polypropylene hybrid fiber reinforced concrete (C-P HFRC), which acted by the bending and tensile stresses, were tested in a Scanning Electron Microscopy (SEM). Fibers pull-out, fiber debonding from matrix and fiber fracture were dynamically observed. The C-P HFRC's failure morphology and processes were described in detail. Results indicate that, in the tensile district, debonding between the matrix and the fiber occurred at approximately 45° to the tensile direction, and a great number of carbon fibers were pulled out, a small number of polypropylene fibers were greatly deformed and fractured. As the C-P HFRC enduring the bending stress, both the carbon and the polypropylene fibers were debonding from the matrix along the fiber latitude, and some of the fibers were fractured. When the stress state was on relatively high level, the stress was always first transferred from the matrix to the carbon fibers. If the carbon fibers could not bear the stress, the polypropylene fibers would undertake most of them and lead to a large amount of deformation induced failure. In the section, where the carbon and the polypropylene fibers were orthogonal distributed, the fibers perpendiculars to the principal stress were fractured by tensile stress, but the fibers parallel to the principal stress had no damage. As a whole, some hybrid effects on the C-P HFRC's macroscopic properties were examined.