Mechanical Properties and Structural Behavior of Bridge Deck Slabs Reinforced with Basalt-FRP Bars

Corrosion is the most common structural deterioration mechanism in any concrete structural element exposed to environmental conditions, particularly in severe weather conditions where deicing salt is used. Basalt fiber-reinforced polymer (BFRP) bars have been gaining the attention of researchers due to their corrosion resistance, high tensile strength, and lightweight compared to conventional steel reinforcement. Another advantage of BFRP is the reduction of concrete cover, leading to a shallower cross-section of concrete. Before adopting BFRP as an alternative reinforcing material, it is essential to study the durability of BFRP bars, the mechanical characteristics, and the bridge deck failure modes depending on the bar size, bar spacing, and reinforcement ratio. Basalt fibers are made from igneous basalt volcanic rocks melted at 1400 oC utilizing a technology similar to those used to produce E-Glass and AR-Glass fibers. BFRP bars are a reinforcing material made from basalt fibers with a resin material for fiber bonding and a sand coat at the surface for bonding with concrete. BFRP bar is an environmentally friendly material and has better resistance to corrosion and freeze and thaw cycles than conventional steel reinforcement, which draws attention to the use of this material in special structural applications. There are current specifications for Glass-FRP, Aramid-FRP, and Carbon-FRP per ACI 440.1R and ASTM D7957 (ACI440.1R-15, ASTM D7957). Since Basalt-FRP revealed the same tensile behavior as the other FRP materials, the future version of the FRP specification can include BFRP. However, there is no study in the literature to understand the effects of bar size on the mechanical and durability characteristics of BFRP bars. In this research, the tensile strength, bond strength and corrosion resistance of BFRP bars are studied. The tensile strength of BFRP bars reveals to be 3-4 times higher than conventional steel with a decrease in the tensile strength as the bar size increases. Moreover, the bond strength is a significant factor in introducing BFRP to bridge deck design to ensure the fixation of the embedded rebar in concrete. The required lap length is identified as 40 times the bar diameter for BFRP bars #4, #5, and #6. Furthermore, BFRP bars can be manufactured in different shapes and forms, allowing the bar to be used as a stirrup in concrete beams. Here lies the importance of studying the shear strength of BFRP bars which is expected to be much lower than the tensile strength. The durability study shows that the resin material used in bar manufacturing and the bar size play essential roles in the bar's resistance to harsh environmental conditions, especially alkaline solutions such as deicing salt. A predictive model for the tensile capacity retention was generated and the residual tensile strength after one million hours of exposure (114 years) is 56% and 87% for bars No. 5 and 6, respectively. It is essential to reevaluate the current construction specification to allow BFRP bars as the primary reinforcement in bridge decks. Although a BFRP bar exhibits a lower modulus of elasticity compared to mild steel reinforcement, it can be incorporated in special applications such as bridge decks where deflection is not an issue. The research study includes the following parameters: bar size and spacing, slab length, and continuity on the behavior of the bridge deck reinforced with BFRP bars. A total of six full-scale single-span and two-span continuous bridge deck slabs were cast in place, instrumented, and tested in the newly built high-bay structures laboratory at UIC. Due to the lower modulus of elasticity of BFRP compared to mild steel, the bridge deck slab design calls for an over-reinforced section to control the section's serviceability at cracking. Unlike traditional concrete design, the concrete crushes in the compression zone before the BFRP bars rupture. The bridge decks were tested and monitored for serviceability, including pre-cracking, cracking, and post-cracking up to their ultimate strength (failure). The collected test results included deflection, crack width, concrete and BFRP bars strains, ultimate flexural capacity, and compression-shear failure mode. A new empirical model of the flexural shear strength for a span length-to-depth ratio of less than 12 was developed for bridge deck slabs reinforced with BFRP bars. The research shows that BFRP bars can be replaced as an alternative corrosion-free material for short span bridge decks. This unique model was validated in four research studies from literature and the equation was in good agreement with the experimental results.