United States Department of Transportation
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BFRP Rebar Characterization and Performance: Testing Protocol and Material Specifications for Basalt Fiber Reinforced Polymer Bars
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2022-07-30
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[PDF-160.88 MB]
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Edition:Final Report 1/18/2019 – 7/30/2022
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Abstract:This research was conducted to evaluate the performance of three commercially available BFRP rebar products and their individual raw material components, before and after exposure to nine different aggressive environments at 60°C for 300d and 600d, to development acceptance criteria specifically for basalt-based fiber reinforced polymer (BFRP) reinforcing bars which can further refine FDOT Specifications Section 932. Three high-quality rebar products from different established FRP rebar producers were selected to evaluate two commonly used rebar sizes (# 3 and # 5) and to fully characterize the relevant material properties. A total of five different physical properties (cross- sectional dimensions, moisture absorption, fiber content, XRF analysis, and glass transition temperature) and four mechanical strength characteristics (transverse shear strength, apparent horizontal shear strength, tensile strength and elastic modulus, and bond-to-concrete strength) were experimentally quantified – for virgin materials, and compared to the aged constituent materials and BFRP rebars. Because acceptance criteria for basalt FRP rebars are not well established in the US, the findings were compared to the prevalent minimum criteria for glass FRP rebars and it was found that BFRP rebars are stronger and more durable than the minimum criteria set for GFRP bars. Performance differences were noted for rebar products from different manufacturers because of dissimilarities in material production and surface enhancement properties. However, basalt fiber rebar products appear to be a viable alternative as a non-corrosive rebar option. A standardized use of such rebars seem feasible based on appropriate acceptance criteria. While the development of acceptance criteria for BFRP rebars has been initiated through this project, and an implementation of this alternative reinforcing technology should be strongly considered by the FDOT, more critical BFRP-specific performance criteria can be developed in future projects to further differentiate the various fiber types and to take full advantage of the available material characteristics. A long-term strength prediction model that estimates the strength retention of FRP bars regardless of exposure environment was developed based on the fib bulletin 40 model. Two new degradation terms, nCl and nt, addressing chloride ion concentration of the exposure environment and exposure time were addressed to determine the environmental degradation factor (CE) for FRP bars. The model was fed with empirical data from BFRP rebar testing in virgin and conditioned state and long-term strength retention was predicted. An interim approach for acceptance of BFRP reinforcing using the current environmental exposure factor CE = 0.7 in design, and a modified Alkaline Resistance test under ASTM D 7957 was proposed.
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