Audit of a road bridge superstructure using ground penetrating radar

摘要

This paper describes a new application of Ground Penetrating Radar (GPR) in non-destructively assessing the delivered quality of bridge superstructure beams. A case history is described where GPR was used to assess the quality of 180 prestressed concrete beams in relation to the requirements specified in the engineering design. The beams analyzed in this project represent a standard design used in Queensland where several large polystyrene blocks (called 'voids') are cast internally within the deck beams to reduce the mass of the beams. GPR was used effectively to determine the finished location of these voids within the beams and identify any defects associated with the movement of the voids during manufacture of the beams. It was concluded that at least 90% of the beams were out of tolerance due to significant void movement in a vertical direction and there were significant associated defects of air cavities within the concrete, thin top and bottom flanges and longitudinal soffit cracking. Predominantly the voids had moved downwards during the concrete placement process. The accuracy of the GPR survey was determined to be $POM 5 mm where good calibration was obtained and $POM 10 mm for the global set of results of 4860 measurement points.