Evaluating the long-term durability of fiber reinforced polymers via field assessments of reinforced concrete structures

Abstract

Fiber Reinforced Polymer Composites (FRP) are an attractive repair option for reinforced concrete structures, however their long term performance in field environments is not well understood. Laboratory durability tests have indicated that FRP generally performs quite well, but these laboratory tests cannot model the synergistic effects that occur when the FRP is in-service on a bridge (or other structure). Field assessments of FRP properties are very rare in the literature. This thesis describes an effort to collect in-situ data about a FRP repaired concrete arch bridge. The Castlewood Canyon Bridge on Colorado state highway 83 was reconstructed in 2003. The reconstruction included replacement of the deck and spandrel columns and repair of the existing concrete arches with externally bonded FRP. The FRP had been in service for 8 years when its condition was assessed for this project. Assessment efforts started with collection of as much information as possible about the materials and techniques used for repair. Unfortunately only limited amounts of initial or baseline data were recovered. Based on available information a tentative plan for site assessment activities was prepared, including testing locations at the base and crest of the arch. The field assessment of the bridge was completed on location during July, 2011. The complete extrados of the east arch was inspected for voids between the concrete and FRP using acoustic sounding and thermalgraphic imaging. Voids that were previously identified during a routine bridge inspection in 2007 had grown significantly larger by the 2011 assessment. Pull-off tests were used to test the bond strength at the base and top of the arch. Pull-off strengths were on average lower and represented different failure modes from pull-off tests conducted at the time of repair. Large debonded regions of FRP were cut from the structure to use in laboratory testing. Damaged regions were repaired with new FRP. Materials brought back from the bridge were used for tensile and Differential Scanning Calorimetry (DSC) testing. The tensile tests showed that the FRP strength was well below the specified design strength, but the lack of initial data makes it difficult to tell if the material has deteriorated over time, or if the material started off with lower strengths due to field manufacture techniques. The DSC tests showed that the glass transition temperature of the composites was near the value suggested by the manufacturer. The field assessment was used as a case study in collecting durability data about FRP. From this case study numerous recommendations are made to improve the available information about the durability of FRP repairs in field environments. A specific process to be followed in collecting this data is also proposed.