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This study intends to establish the mechanical properties of polyamide fiber reinforced shotcrete (PAFRS) in terms of compressive and flexural strengths, in accordance with ASTM C1609/C1609M-12. The mechanical properties identified the influence of polyamide fiber content on the PAFRS strength. This study evaluated the toughness of PAFRS and proposed additional toughness level criteria to better represent organic fiber performance. In addition, the fiber rebounding rate and PAFRS performance in tunneling application were evaluated based on a tunnel application in Korea. PAFRS with 0.6%~0.8% volume content in tunneling shotcrete could significantly improve flexural ductility, toughness, and ultimate load capacity. Fiber rebounding tests exhibited a low rebounding rate (8.5%) and low fiber drop (63.5%). Therefore, PAFRS applied to a tunnel exhibited stability and constructability.

This study developed a macro-sized polyamide (PA) fiber for concrete reinforcement and investigated the influence of the PA fiber on flexural responses in accordance with ASTM standards. PA fibers are advantageous compared to steel fibers that are corrosive and gravitated. The macro-sized PA fiber significantly improved concrete ductility and toughness. Unlike steel fibers, the PA fibers produced two peak bending strengths. The first-peaks occurred near 0.005 mm of deflection and decreased up to 0.5 mm of deflection. Then the bending strength increased up to second-peaks until the deflections reached between 1.0 and 1.5 mm. The averaged flexural responses revealed that PA fiber content did not significantly influence flexural responses before L/600, but had significant influence thereafter. Toughness performance levels were also determined, and the results indicated more than Level II at L/600 and Level IV at others.

A concrete shear wall system is an ideal structural system that can effectively resist large horizontal cyclic loads such as earthquakes. In particular, a significant increase of the ductility in fiber reinforced concrete shear walls can prevent a brittle failure and thus can enhance seismic resisting capacity significantly. This study investigated the shear resisting capacity of shear wall specimens, which are constructed with steel fibers or polyamide fibers reinforced concrete, by comparing hysteresis curves obtained from reversal cyclic tests. The shear resisting force in the steel fiber reinforced concrete specimen was larger than those in plain and polyamide fiber reinforced concrete specimens, but the increase was not great. The shear resisting capacity of the polyamide fiber reinforced concrete specimen was larger than that of plain concrete specimen, but smaller than that of steel fiber reinforced concrete specimen.

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