Assessing the Hybridization Effect of Fibers on the Mechanical Properties and Durability of Concrete

Abstract

Fiber-reinforced concrete has gained wide attention in the past years. The need for a high-performance and ductile construction material led to the advance in research and application of fibrous concrete. Fibers are short filaments that can be natural, metallic, glass, or polymers (like polypropylene or polyvinyl alcohol). The addition of one type of fibers could improve the performance of concrete. Yet, the incorporation of more than one fiber type in the concrete mixture can create a synergetic effect that could further enhance concrete’s properties. A multi-phase research program was conducted at the American University of Beirut to study fiber-reinforced concrete. The first phase examined the properties of single-fiber-reinforced concrete with variable fiber types and dosages. Four master students worked on that phase and reported the results in their theses. Based on the findings of the first phase, a second phase was designed in which seven mixtures incorporating different combinations of hybrid fibers were tested for: (1) mechanical properties including compressive strength, splitting tensile strength, flexural strength, and elastic modulus; (2) durability properties including resistance to rapid freezing and thawing, thermal conductivity, and water absorption; and (3) shear strength, bond strength, and ductility of the mode of failure of structural members. The fiber types included in the study are Basalt (B), Steel (S), Polyvinyl alcohol (PVA), Polypropylene Econo-Net (PP), and Glass (G). Test results of the hybrid fiber-reinforced concrete mixtures were analyzed and compared with the plain concrete and single fiber concrete mixtures. This thesis reports on Parts 1 and 2 of the above-described scope. Results indicated that whereas hybridization of fibers imposed a negative effect on the compressive strength, however it significantly enhanced the tensile and flexural strengths and remarkably improved the durability of the tested concrete specimens.