Evaluating Prestressing Strands and Post-Tensioning Cables in Concrete Structure Using Nondestructive Methods.

摘要

The objectives were to evaluate the ability of different NDE methods to detect and quantify defects associated with corrosion of steel reinforcement and grout defects in post-tensioning applications; and to evaluate the effectiveness of selected NDE methods to detect and quantify the deterioration. The study included side-by-side box beam bridges for evaluation of the condition of prestressing strands and web reinforcement. Decommissioned box beams were tested in the laboratory to relate the quantified deterioration to the measured residual flexural capacity. Also a segmental bridge was included for evaluation of the condition of the web reinforcement and post-tensioning ducts. Laboratory specimens simulated debonding and voids around steel reinforcement, loss of cross section area of steel reinforcement, and various grouting challenges. The NDE methods used were (1) ultrasonic testing for delamination/void detection; (2) electrochemical measurements for assessing the corrosive environment; and (3) magnetic flux leakage (MFL) to estimate loss of cross sectional area of embedded steel. Ultrasonic echo-pulse tomography was able to detect debonding of the steel reinforcement and to detect internal voids and delamination. The method was able to quantify the depth of the defect but not the defect length. Electrochemical testing isolated the areas with high chance of corrosion. The MFL pilot demonstration showed that MFL can detect changes in the area of the steel reinforcement in laboratory and field applications. Presently, the calibration overestimates the steel loss. There was good agreement between estimated beam flexural capacity based on NDE results and the measured capacity of full scale box beams.