# Experimental Crack Width Quantification in Reinforced Concrete Using Ultrasound and Coda Wave Interferometry

## TL;DR

This study uses ultrasound and coda wave interferometry to measure crack widths in reinforced concrete under tension, offering a new method for infrastructure health monitoring.

## Contribution

The first direct proportional relationship between ultrasonic velocity changes and crack widths in reinforced concrete is established.

## Key findings

- A direct proportional relationship between ultrasonic velocity change and crack widths was found during crack formation and stabilized cracking.
- Linear correlations between velocity change and average strain, as well as specimen length, were observed in the non-cracked state.
- The study enhances understanding of ultrasonic signal behavior in reinforced concrete during cracking.

## Abstract

For the first time, comprehensive investigations into the tensile load-bearing behavior and crack formation of reinforced concrete based on ultrasound are presented. Uniaxial tensile tests are performed on reinforced concrete tension members equipped with embedded ultrasonic transducers. Key mechanical parameters across all ranges of tensile behavior are continuously quantified by recording ultrasonic signals and evaluated with coda wave interferometry. The investigations include member configurations of different lengths to cover different numbers of cracks. For reference, crack patterns and crack widths are analyzed using digital image correlation, while the strain in the reinforcement is monitored with distributed fiber optic sensors. For the first time, a direct proportional relationship between the relative velocity change in ultrasonic signals and crack widths is established in the ranges of crack formation and stabilized cracking. In the non-cracked state, linear correlations are found between the velocity change and the average strain, as well as the length of the specimens. The experimental results significantly enhance the general understanding of the phenomena related to ultrasonic signals in flexural reinforced concrete members, particularly concerning cracking in the tensile zone. Consequently, this study contributes to the broader objective of employing coda wave interferometry to evaluate the condition of infrastructure.