Experimental Study on the Effects of Addition of Polypropylene Fibers on Mechanical Properties of High Strength and Normal Strength Concrete

The use of thermoplastic polymers to improve characteristics of concrete has gained attraction over the last couple of decades. Polypropylene fiber is a type of thermoplastic that is considered to have added desirable properties to concrete. In this thesis, the effects of Polypropylene fiber on fresh and hardened properties of normal strength concrete, and high strength concrete were investigated. Different percentages of Polypropylene fiber were added by volume (0, 0.25, 0.50, 0.75, and 1.00 %) to normal strength and high strength concrete, water to cement ratio of 0.5 for normal strength concrete and 0.4 for high strength concrete. Slump and VeBe time tests were performed to analyze the physical properties of fresh concrete, while the effect of polypropylene fibers on the mechanical properties of hardened concrete was executed by performing compressive strength test, flexural and toughness test, splitting tensile strength test, drying shrinkage test, heat degradation test (100 °C, 200 °C), Schmidt hammer test, Ultrasonic Pulse Velocity test (Pundit), water absorption test, and water permeability test. The results show changes in mechanical properties of normal strength concrete and high strength concrete as the percentages of PPF increases. However, improvement in mechanical properties were identified after the analysis. Compressive strength of normal strength concrete decreased at 28 days while that of HSC increased as Splitting tensile strength for both concretes increased as percentage of polypropylene fiber increased at 28 days. There was increase in flexural strength and toughness in both normal and high strength concrete as polypropylene fiber percentage increases, except for 1.00 % which showed decrease. Less penetration depth was observed with the addition of fibers. Pundit test showed results of a good concrete quality with Polypropylene fiber before and after heat exposure. Decrease in compressive strength, splitting tensile strength, and ultrasonic pulse velocity was observed after 100 °C and 200 °C heat exposure. Keywords: Polypropylene Fibers (PPF), Normal Strength Concrete, High Strength Concrete, Mechanical Properties, Shrinkage, Water absorption, Permeability, Heat exposure.