Potential of InfraRed Thermography for delamination detection in hybrid concrete structures

Abstract

The concrete bridges constructed in the 1960s and 1970s lack shear reinforcement, rendering them non-compliant with current design regulations. To potentially enhance their shear capacity, the proposed approach involves applying a layer of ultrahigh-performance fiber-reinforced concrete (UHPFRC) on both sides of the normal strength concrete (NSC) beams supporting the bridge deck. A crucial aspect of this method is ensuring a high-quality connection between the UHPFRC layer and the NSC beam to transfer shear stresses effectively. Therefore, the report explores the feasibility of employing active infrared thermography (IRT) as a non-destructive testing (NDT) method to identify delaminated areas within this interface.
The primary objective of this report is to answer the question: "Is it possible to detect and quantify delaminated areas, within the connection between a NSC beam and a layer of UHPFRC of a certain thickness in an objective way, with data gathered by an infrared camera in a lab environment?"
The report outlines the chosen approach for detecting delaminated areas, establishes a standardized testing methodology, and formulates an analytical model to process the data gathered during experiments conducted based on the established standards. The data collection process involves utilizing an infrared camera to measure the temperature of every pixel in each frame of a recording.
From literature review and a qualitative comparison of different methods to detect delaminated areas, the signal-to-noise ratio (SNR) method is chosen in this report. The SNR method compares the temperature in a specific area to that of a sound area while considering the standard deviation of temperature in sound areas, accounting for environmental factors.
The analytical model developed in the report identifies delaminated areas when infrared camera recordings are available. To ensure objectivity, a standardized approach for heating and cooling the specimens is established. Heating is achieved with a heat flux of 1750 W/m² on the UHPFRC layer's surface for 1500 seconds, followed by recording the cooling process with an infrared camera. The analytical model selects the optimal frame for analysis based on this data together with data gathered from a finite element analysis performed in the software COMSOL Multiphysics 5.6.
The report distinguishes between two situations: one where the location of a sound area is known, and another where it is not. The analytical model produces promising results for both scenarios, with simulated delaminated areas visible in the test samples. However, in cases where the location of sound areas is unknown, the model may underestimate the size or extent of delamination, especially in nearly fully delaminated structures. Further research is recommended to assess the accuracy and applicability of the method in situations where sound area locations are unknown and to determine the model's minimum detectable delaminated area.