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Pull-out Strength of Fiberglass/Epoxy Composite Rebar Manufactured Using a Three-Dimensional Braiding Process



This research demonstrated the ability to produce high quality fiberglass-epoxy rebar using a continuous three-dimensional braiding process. The tensile pull-out strength of the composite rebar embedded in concrete was measured and compared to steel rebar. Fiberglass/epoxy is less likely to corrode than steel rebar, ensuring more sustainable concrete structures in infrastructure applications. The 0.5” diameter composite rebar was produced by pulling hundreds of strands of unidirectional fiberglass/epoxy towpreg to form the core of a cylindrical rod. The rods were consolidated by overwrapping strands of aramid fiber under tension in a spiral fashion, and cured using the manufacturer’s (TCR Composites) recommended 250°F cure cycle. Configurations manufactured and tested included tow variations of aramid overwrap (dry and prepreg) with and without sand coating embedded in concrete cubes (8”x8”x8”). The results are compared to baseline values obtained by testing traditional steel rebar and commercially-available fiberglass composite rebar. The tensile pull-out (bond) strength was quantified using a test fixture in accordance with ACI 440.3R-12. Measurements were collected at both the free and loaded ends of the rebar, with freeend results yielding a more accurate indication of rebar bond stress. The bond strength of the in-house manufactured fiberglass/epoxy rebar was comparable to steel rebar and commercial fiberglass composite rebar. The sand coating increased the surface roughness, improving the bond strength of the composite rebar by margins of 43-58% percent. Fiberglass/epoxy composite rebar consolidated with prepreg aramid tow and subsequently coated with sand resulted in a bond strength slightly higher, but comparable to steel. This study demonstrates the ability to consistently produce high quality fiberglass/epoxy composite rebar using an innovative, low cost, high production rate, three-dimensional braiding process.


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