Conference Agenda

The three-dimensional images made possible by techniques such as x-ray computed tomography continue to provide us with new insights into fracture processes in concrete. Over the past 30 years, advances in both image acquisition and image analysis have improved to the point in which CT-based experiments are becoming relatively commonplace. In this work, we review some image analysis advancements and how they can be used to quantify the internal mechanisms that contribute to the complex problem of energy dissipation. The case study presented features a high-performance concrete with hybrid reinforcing consisting of conventional steel fibers, micro (steel wool) fibers, and a hybrid combination of both. 50-mm diameter specimens were loaded in a split-cylinder configuration at quasi-static and low-velocity impact rates. The 3D image analysis broke the crack measurement problem into two parts: macro-cracking and micro-cracking. In this case, macro-cracks were defined as those visible in the images, while micro-cracks were those not visible. An edge detection algorithm was employed to measure macro-cracks, while a digital volume correlation method was used to estimate micro-cracking. Results showed a shift in micro-crack to macro-crack ratio as strain rates increased, although the result are highly dependent on the nature and orientation of the fiber reinforcements.

In recent years, local Digital Image Correlation has become a standard method to monitor cracks in concrete samples during laboratory tests, aiding the understanding of fracture mechanisms. The significant challenge is to efficiently and accurately evaluate crack characteristics from the DIC displacement field. Most existing methods, when they do not employ machine learning techniques in the middle, start with crack extraction. This is usually based on DIC residuals, strain analysis or image processing. The discontinuity kinematic can then be evaluated using points on both sides of the crack and usually require prior crack local frame computation in addition. This paper applies a streamlined method for crack measurement to four-point bending tests on RC beams. The method bypasses the need for crack geometry extraction, local frame calculation and point selection, directly analyzing the full displacement gradient field. Taking advantage of the rather simple displacement field around cracks, the local crack kinematics—such as opening, slip, and orientation—are continuously calculated at all displacement points. The opening and slip measures are maximal along cracks, allowing easy crack extraction after crack kinematic evaluation. RC beams with varying shear reinforcement ratios are studied, demonstrating the method’s capability to analyze complex crack patterns. Furthermore, this procedure can be easily adapted for 3D Digital Volume Correlation (DVC) displacement fields obtained from microtomography with minimal modification, offering broader applicability to both experimental and numerical displacement fields, an advantage over conventional methods.

Cables in engineering structures are essential to the integrity of the structure. However, they are subject to damage in specific areas, particularly at the cable entry into the anchor base. Currently, there are no non-destructive testing techniques available for examining this area. The aim of this work is to study the feasibility of defect detection using acoustoultrasounds. These combine ultrasound and acoustic emission. Tests on suspension bridges have shown that the technique is sensitive to the state of health of the bases. However, in order to quantify the nature of the defect and determine its severity, a study is being carried out on ”model” anchor bases, manufactured on a real scale: two bases without defects and four reproducing defects observed during inspections of bridges (mechanical failure and corrosion of the cable’s external wires, presence of a void in the fusible material). The first step was to optimise the choice of sensors for transmission and reception and their position. Then, a detailed analysis of the descriptors extracted from the signals is carried out to determine the presence of a defect and assess its severity.

This study presents the transformation of acoustic emission (AE) waveforms from time domain to frequency domain using fast fourier transform (FFT) to understand the mechanisms underlying the fracture of cementitious composites. The motivation of the study is to introduce a real-time monitoring method based on frequency content of AE. The mode I fracture experiments are performed on plain concrete (PC) and steel fiber reinforced concrete (SFRC) in the laboratory. The fracture mechanisms of PC and SFRC are analyzed using the centroid of the frequency spectrum obtained from spectral analysis. The results indicate that there is no change in the frequency centroid spectrum (FCS) until the onset of microcracking in mode I crack deformation. After the microcracking begins, the slope of the FCS continuously decreases, indicating the rate of material damage over time. An accelerated crack growth denoted by slope of mean FCS is 2.7 times higher for PC when compared with SFRC. The slope of the mean FCS is nearly the same for both the initial and final regions of fracture mechanisms in PC. In SFRC, this rate is 29.2% lower due to fiber bridging mechanisms. A damage parameter, based on the FCS, is proposed to assess the damage and validated with the existing damage parameters. These observations suggests that FCS of AE waveforms may be used for real time damage monitoring of concrete structure.