Experimental Methods to Detect and Quantify Damage in Restrained Concrete Ring Specimens

Abstract

This paper describes the use of three experimental methods to detect shrinkage cracking in restrained ring specimens. These methods include monitoring the strain at the inner surface of the restraining steel ring, using passive acoustic emission, and measuring the electrical resistance of conductive materials that are applied to the surface of the mortar. The methods for detecting cracking are compared and their advantages and limitations are discussed. Both plain and steel fiber reinforced (2% steel fiber by volume) mortar were evaluated in this study. The time of through cracking detected by the three methods corresponds to the time of visible cracking. In the mixtures containing fibers the time of through cracking is delayed significantly when compared to the plain systems. The delay in the age of through cracking can be explained by the role of fibers in arresting the cracks as they develop and their role in transferring stress across the crack width that keeps the cracks from opening. The passive acoustic emission data indicates substantial damage development before a through crack forms. The time of through cracking can be detected using conductive surfaces with a sudden increase in resistance of these conductive elements. Cracking can be detected using conductive coatings when the crack is 0.02 mm or larger. Specimens with different degrees of restraint show through cracking at approximately the same stress level; however, the age at which cracking occurs decreases as the degree of restraint increases. This can be attributed to the increased micro-cracking (i.e., damage and precritical crack growth) as confirmed with acoustic emission data.

A functionally layered sensing skin for the detection of corrosive elements and cracking

“…5 Conductive surface sensors have been recently developed for crack detection in both one-and twodimensional (1D and 2D) settings. 1D sensors are usually made of strips of conductive materials, [5][6][7][8][9][10][11][12][13] while a 2D sensor (also referred to as a sensing skin) consists of a patch of conductive material and an array of electrodes on the patch perimeter. [14][15][16][17][18][19][20][21] While the above-mentioned 2D sensors use EIT to reconstruct the spatial conductivity (or resistivity) distribution, other types of 2D sensors have also been developed.…”

Boundary Deformation Measurement by Mesh-Based Digital Image Correlation Method

“…Thus, the deformation near the curved edges is particularly important in mechanical or failure analyses. For example, for a ring component under diametrical compression, cracks initiate from the hole edge owing to the local stress concentration [5]. From this perspective, the accurate measurement of deformations near or on the curved edges of specimens or structures plays a very important role in practical applications.…”

Electrical impedance tomography-based sensing skin for quantitative imaging of damage in concrete

“…Raoufi et al [30] compared the performance of these 1D conductive surface sensors in crack detection with acoustic emission and image analysis techniques during shrinkage cracking tests, and used these sensors as a method to study the effect of the bonded substrate length on crack opening. Previous studies [30,31] have shown that the time of visible cracking is captured accurately by conductive surface materials. Recently, more advanced methods such as radio frequency identification [32] and frequency selective circuits (FSC) [33] have been used in conjunction with these 1D conductive surface sensors for damage detection in concrete materials and reinforced concrete elements.…”