Flexural Performance Evaluation of Fiber-Reinforced Concrete Incorporating Multiple Macro-Synthetic Fibers

Abstract

Fiber-reinforced concrete (FRC) is a promising construction material mainly because of the crack-controlling mechanisms that discrete fibers can impart to inherently brittle concrete. Macrofibers, in particular, have been proven effective for providing post-crack ductility and toughness, while synthetic fibers are a promising solution to avoid corrosion-related durability issues. To assess the performance enhancement provided by macro-synthetic concrete fibers, this study performs flexural tests on FRC beams containing three different types of macro-synthetic fibers. The selected fibers include polypropylene (PP), polyvinyl alcohol (PVA), and alkali-resistant glass (ARG) macrofibers mixed at volume fractions of 0.5%, 1.0%, and 1.5%. Static and dynamic fresh properties are monitored using the vibrating Kelly ball (VKelly) test. Beam specimens are then placed under a third point bending configuration, as per ASTM C1609 Standard, to measure load versus mid-span deflection. Strength and toughness parameters are derived from the load–deflection data to assess the flexural performance of the FRC composite systems under consideration. The parameters of interest include first peak strength (pre-crack flexural strength) and post-crack residual strength and toughness provided by fiber addition. Of the mixtures tested, ARG fiber mixtures show the highest residual strength and toughness values, followed by PP and PVA fiber mixtures. ARG fibers produce the most workable mixtures at all fiber volumes, while PVA fibers show a tendency to encounter dispersion issues at higher volume doses. The outcome of this study is expected to facilitate the selection of fibers by giving insight into their relative contribution to fresh and hardened flexural properties of FRC.

State-of-the-Art Review of Capabilities and Limitations of Polymer and Glass Fibers Used for Fiber-Reinforced Concrete

“…However, this was found highly dependent on fiber dimensions and the mixture design. Dopko et al [ 5 ] had a similar observation, indicating that PP macrofiber additions above 1.0% fiber volume greatly reduce the workability of FRC. In a comparison between PP and nylon fibers (used with a similar dosage in concrete), it was reported by Heo et al [ 107 ] that the addition of PP fibers has a notable effect on the workability of FRC.…”

“…The cited study was able to achieve satisfactory workability characteristics with 3.0% PVA fiber volume. Dopko et al [ 5 ] reported difficulties when mixing macro PVA fibers in concrete at volumes over 1.0%, indicating that the fibers tend to re-aggregate and form clumps once a critical volume is reached. The cited study also found that PVA fibers decreased workability and caused dispersion issue at the same fiber volume of PP fibers, even though the PP fibers had a higher aspect ratio than the PVA fibers.…”

“…Noushini et al [ 138 ] showed that 0.25% PVA fiber addition increases the compressive and splitting tensile strengths of FRC, while any further increase in the fiber content can have counter effects on the strength. The splitting tensile and flexural strengths of FRC have been reported by several studies to remain the same or experience an increase with the addition of PVA fibers [ 5 , 108 , 109 , 137 ]. However, Yeganeh et al [ 136 ] reported a drop in the flexural strength of FRC, although an increase in the splitting tensile strength was noted.…”

“…Several studies have reported significant increase in the post-crack residual strength and toughness of FRC, as a result of macro PP fiber addition [ 5 , 144 , 146 , 180 ]. Cengiz and Turanli [ 181 ] tested the toughness, energy absorption, and ductility of shotcrete panels reinforced with steel mesh, steel fibers, and high-performance PP fibers (with a low modulus).…”

“…Due to the micro-scale reinforcement action provided by microfibers, it is generally accepted that they most significantly affect the strength properties of FRC prior to full crack formation, as characterized by the stress-strain curve prior to the peak stress. Ultimate strength gains in both compression and tension have been reported for FRC with microfiber [ 3 , 4 , 5 ], depending on the fiber and matrix properties. Considering that concrete strength increases over time, even low-modulus microfibers can be effective at increasing the strength at an early age.…”