Experimental study on the influence of polypropylene and steel fiber on flexural behaviours of high strength concrete beams

Abstract

Many properties of plain concrete are readily enhanced by adding various fibers. Different types of fibers were added to improve its tensile and bending behaviours. In the present experimental study, four different fiber dosages of polypropylene (0.025, 0.050, 0.075, and 0.10%) and steel fiber (0.25, 0.50, 0.75, and 1.00%) considered to determine the optimized content of 0.05% of polypropylene and 0.75% (both by volume of concrete) of steel fiber based on the workability and strength test results. These fiber content were added in controlled concrete of 60 MPa compressive strength to observe the improvements in flexural behaviour. Set of three reinforced concrete beam specimens of dimension 200 × 300 × 2100 mm were casted for considered series: controlled concrete (CC), polypropylene fiber reinforced concrete (PFRC) and steel fiber reinforced concrete (SFRC). Four-point bending test was conducted on all specimens by continuously recording the mid span deflection using liner variable differential transformer (LVDT). Primarily, load vs deflection response was plotted to analyze the improvements in, energy absorption capacity, flexural toughness, ductility and post-peak energy dissipation. The cracking pattern was studied in terms of crack width, spacing and number. Results indicated, increased average load sustaining capacity of CC specimen from 58.4 kN to 70.5 kN and 110.6 kN in PFRC and SFRC respectively at yield point. The magnitude of ultimate load enhanced by 12.1 kN in PFRC and 50.1 kN in SFRC specimens. Normalized flexural toughness values increased by 14.86% and 23.51% in PFRC and SFRC. The total energy absorption capacity of CC samples improved by 689.57 kN-mm due to polypropylene fiber and 2271.89 kN-mm because of steel fiber addition. The CC, PFRC and SFRC series displayed 1892.96 kN-mm, 2184.19 kN-mm and 2956.15 kN-mm of energy dissipation in the post-peak region. Steel fiber inclusion indicated the branching of cracks from the primary cracks.