Detection and evaluation of heat damage in reinforced concrete beams using linear and nonlinear guided waves

Abstract

This study utilizes the linear and nonlinear features of guided waves (GWs) for detecting and evaluating heat damage in reinforced concrete (RC) beams. The RC beams with embedded sensors attached at rebar ends are experimentally studied using longitudinal GW at 200 kHz after heating the specimens in a furnace from 100°C to 300°C. For the studies investigating the effect of heat damage on the RC beams beyond 300°C, the rebar ends are exposed outside the concrete so that the longitudinal transducers can be attached there. These specimens are then experimentally studied using GW with an excitation frequency of 100 kHz. In this study, the RC beams are prepared as fully bonded and debonded specimens. The experimental study shows that heat damage in the RC beams causes debonding between rebar and concrete enabling GW signal to generate second harmonics. The experimental study also discussed the linear features of GW, which shows that the amplitude of the GW signal increases with elevated temperatures in the RC beams. To distinguish material nonlinearity and contact nonlinearity, two types of nonlinear parameters are defined in this study. The nonlinear parameter due to the contact acoustic nonlinearity effect in the RC beams is defined as β, whereas the nonlinear parameter due to material nonlinearity is defined as β m. The study shows that β m is negligible in comparison to β at relevant heated temperatures. With the increase in temperature, the nonlinear parameter β is significantly increased at elevated temperatures. The peak amplitude of the nonlinear parameter β is observed at the maximum heated temperature 800°C for both bonded and debonded specimens.

Experimental study of heat damage evaluation using nonlinear ultrasonic guided waves

“…The measured time domain signals can then be transformed to frequency using the Fast Fourier transform. Using the frequency domain data, a nonlinear parameter b can be defined to evaluate the debonding between the rebar and the concrete [14].…”

“…The dimension of the reinforced concrete specimen is 400 mm ´ 75 mm ´ 75 mm, and the rebar is 300 mm long with 24 mm diameter. 20 mm diameter and 2 mm thick PZTs are attached to both ends of the rebar using conductive epoxy [14]. This study used high temperature epoxy resin to protect the PZTs and the ceramic fiber thermocouple cables are used to establish an electrical connection between the equipment and PZTs The guided wave excitation and measurement are initially conducted on the specimen at room temperature.…”

“…This study used high temperature epoxy resin to protect the PZTs and the ceramic fiber thermocouple cables are used to establish an electrical connection between the equipment and PZTs The guided wave excitation and measurement are initially conducted on the specimen at room temperature. Subsequently, the reinforced concrete specimen is heated with regular intervals in an electric furnace to desired temperatures, maintaining it for 2 hours before gradually the temperature is reduced to 100°C at 10°C/min [14]. The heated temperatures considered in this study are 100°C, 200°C and 300°C.…”

“…They proposed to use the combinational harmonic generation of the Rayleigh wave due to the contact nonlinearity at debonding between the CFRP and concrete for damage detection. This paper aims to provide a summary of the key results of a recent study [14], which focused on using second harmonic generation due to longitudinal guided wave interaction with debonding between the rebar and concrete caused by heat damage in a reinforced concrete beam.…”