Effect of rebar geometries on ultrasonic waves propagation in reinforced concrete structures using finite element method

Abstract

Corrosion of steel rebar in reinforced concrete (RC) structures introduces internal stress at the interface between rebar and concrete, ultimately leading to the failure of structures. Detection of early-stage corrosion of steel rebar can significantly reduce maintenance cost and risks. An active photoacoustic fiber optic sensor system had been proposed for early-stage corrosion detection of steel rebars by generating and receiving surface ultrasonic waves. However, the implementation of a corrosion detection method requires knowledge of surface ultrasonic waves propagating at rebar-concrete interface. The objective of this study is to investigate the interaction of surface ultrasonic waves with local geometries (of a number four rebar) and concrete covers using the finite element method (FEM). In this study, seven three-dimensional finite element models were created to simulate surface ultrasonic waves propagating in three different cross-sections of a steel rebar with different concrete cover. Three lug locations and three types of concrete (differed by Youngs modulus) were considered. The pitch-catch mode was adopted, in which one source and one receiver were deployed at each rib of the rebar. 1 MHz sinusoidal pulse was introduced at the source while time domain radial displacements were collected at the sensor. Short-time Fourier transform was used to analyze collected time domain radial displacements. From our simulation results, it was found that high frequencies of ultrasonic waves were affected by lugs more than lower frequencies. Presence of concrete cover suppresses the amplitude of surface ultrasonic waves.