Performance of FRP-strengthened reinforced concrete beams subjected to low temperature

Abstract

The use of Fiber Reinforced Polymer (FRP) to repair and strengthen existing concrete structural elements (beams, columns, beam-column connections, and slabs) has become globally accepted and popular. FRP can be used for this application in several forms, such as externally applied wrapping, Near Surface Mounted (NSM) bars, lamination, and sheets. The strength to weight ratio of this material is one of the main criteria that makes this material approved and desired by engineers and researchers for this application. Also, FRP is corrosion resistant and requires less installation time compared to other repairing techniques such as jacketing, section enlargement, and external post tensioning. The performance of FRP repairs has been studied extensively at conventional, non-extreme temperatures; however, little research has been conducted on the performance of these repairs at cold temperatures. The research discussed herein aims to fill this gap in knowledge so that FRP repairs can be more widely used in cold temperature environments, such as for bridge repairs in the state of Montana. In this work, six beams (6 in. x 8 in., 10 ft long) were constructed and tested in four-point bending at two different temperatures (room temperature and -40 °C). For each temperature, there were three beam types: 1) a control beam, 2) a longitudinal strengthened beam, and 3) a longitudinal + transverse strengthened beam. Overall, the results showed that low temperatures have a generally positive effect on concrete strength and beam performance. The average concrete compressive strength of frozen cylinders at -40 °C was observed to be 87.18% higher than the cylinders tested at room temperature. For all beam types, the ultimate load carrying capacity of the low temperature beams exceeded the capacity of the counterpart beam tested at room temperature. Additionally, at lower temperatures the strengthened beams showed delayed FRP delamination (occurring at higher displacements). Further, the initial stiffnesses of the cold beams were found to be significantly higher than the room temperature beams. Overall, the results of this study are promising for the potential of use of FRP for repairs in cold environments and future research is warranted.