This research employs 3D printing and Digital Image Correlation technology to examine the behavior of rock-like specimens with nonpenetrating long joints under uniaxial compression. It analyzes crack propagation and mechanical mechanisms, revealing joint closure and slip behavior during compression by summarizing surface displacement features. Findings demonstrate the significant influence of the number, penetration depth, and arrangement of nonpenetrating joints on mechanical performance. The displacement X field shows high sensitivity to arrangement type and penetration depth, while displacement Z is particularly sensitive to arrangement. Nonpenetrating joints inhibit displacement X discontinuity locally, globally attenuate displacement Y, and promote displacement Z overall. Pre-existing joints are categorized into main and subordinate joints. Joint closure and slip behavior are not primarily at the tips; the main joints exhibit a top-middle-bottom sequence, while subordinate joints show bottom-middle-top. The nonpenetrating constraint effect on joint closure and slip capacity is influenced by the relative penetration depth of horizontally adjacent joints, both main and subordinate. Consequently, under subordinate joint control, wing extension cracks develop, characterized by a pure tensile mechanism and obliquely parallel cracks exhibiting a tensile-shear mechanism, resulting in four distinct failure modes on the frontal face. Nonpenetrating joints, forming the significant spalling surface, induce noncoplanar extension cracks on the lateral face, exacerbating surface spalling on the back face. The presence of Nonpenetrating joints enhances strength in symmetric specimens but weakens it in asymmetric ones. The joint parameter defined by the penetration rate and type exhibits a monotonic negative correlation with peak strength. This study provides compelling evidence that specimens with nonpenetrating joints replicate layered step path failure surfaces.

In classical mechanical tests, such as tensile tests, elongation and force are measured. Together with the initial length and cross-sectional area, a stress-strain curve is derived. Additional sensors can capture further changes in the material. For example, fractures can introduce elastic waves, which are captured by acoustic emission sensors. We demonstrate how acoustic emission can be applied in mechanical tests using different sensor positions and oscilloscopes. Furthermore, the correlation between mechanical tests and other sensor responses, such as electrical resistivity, temperature, and active ultrasound (combined with coda wave interferometry), is investigated. In the end, we explore the feasibility of controlling the tensile testing process based on sensor signals.

An experimental fracture study was performed on different types of high performance concrete with the objective of measuring the changes in damage and cracking patterns as a function of loading rate. The specimens were 50-mm diameter cylinders prepared with hooked steel fibers, steel wool fibers, and a combination of both. Specimens were loaded in a split-cylinder configuration at three loading rates ranging from quasi-static to drop weight impact. Each specimen was scanned using x-ray computed tomography (CT) both before and after loading such that internal damage could be measured. Fiber orientation relative to the load axis was measured from the CT images, and for each specimen scanned, an “optimum” and “pessimism” orientation was established, the former being the orientation at which the fibers oriented in a way that best resists crack growth, while the latter is the orientation in which the fibers least resist crack growth. Damage measurements were made through a 3D analysis of load-induced crack area using a hybrid edge-detection/connected components analysis. 3D digital volume correlation was applied to measure strains such that damage below the crack detection threshold could be inferred. Results showed that specimens loaded at higher strain rate produced wider cracks, as compared to the lower strain rate specimens. The pessimism fiber orientation specimens also produced larger cracks when compared to its optimum counterpart. It was also observed that cracking was less continuous in steel wool and fiber reinforced specimens than in the purely fiber reinforced specimens. These quantitative measurements of damage could then be compared to the total energy dissipated by the specimen, as determined by load-deformation or impact energy. Optimum oriented specimens dissipated more energy with smaller total crack area, suggesting a larger amount of micro cracking. Indeed, these specimens had higher amounts of residual strain as measured using digital volume correlation.

This contribution studies the evolution of internal damage in fresh cement mortar during the 25 hours of hardening using the in situ timelapse X-ray computed micro-tomography (µXCT) imaging method. During µXCT scans, hydration heat was measured, providing insight into internal damage evolution with a link to the development of hydration heat. The measured hydration heat was compared with an analytical model which showed a relatively good agreement with the experimental data. Using 20 CT scans acquired throughout the observed cement hydration, it was possible to obtain a quantified characterisation of the porous space. Furthermore, the use of timelapse µXCT imaging for 25 hours allowed to study crack growth inside the meso-structure including its volume and surface. Using obtained CT data, a digital volume correlation (DVC) was done to calculate boundary conditions, 3D displacements, and 3D strains. The observed results provide valuable information on the shrinkage of cement mortar.

This paper introduces a novel method for quantitatively assessing fatigue damage in cement mortar by integrating X-ray Computed Tomography (XCT) with Unified Mechanics Theory. Traditional approaches for damage evaluation have relied on empirical equations, lacking mechanistic explanations and requiring extensive experimental data. Computational models offer insight into mechanisms but often lack practical applicability. Unified Mechanics Theory provides a promising alternative, offering a physics-based, non-empirical framework by unifying Newton's laws and the second law of thermodynamics from first principles.

In this study, we compare various damage measures and employ a Unified Mechanics Theory-based model to predict damage, leveraging time-resolved data obtained through XCT. This approach enhances a fundamental understanding of fatigue damage mechanisms in cement mortar. Future research will focus on refining the method and extending its applicability to a broader range of materials and loading conditions.

Corrosion of reinforcement steel in concrete is a common, yet complex, problem. Exposure conditions, such as availability of moisture, chloride, CO₂, and oxygen, and local conditions at the steel-concrete interface, influence corrosion development. Furthermore, as the process takes place inside the concrete, the location of the anodic area is seldom known.

During corrosion, corrosion products, often in form of iron oxides, are produced. Iron oxides occupy more volume than the iron they originated from, leading to internal forces and microcracking. Up to the point when corrosion leads to the formation of corrosion-induced cracks, corrosion is difficult to track.

Observing corrosion development at the steel-concrete interface and the consequent fracture of the concrete is challenging. Destructive tests are by far the most common way to assess corrosion damage, thereby not allowing for the collection of data over time in the same sample. Corrosion potential and current are often used for monitoring the risk and progress of corrosion but can only give a rough estimation of damage distribution.

Imaging techniques have the potential to resolve many of these issues. In this study, the authors will make use of X-ray tomography to study the corrosion development at transverse cracks over time in reinforced concrete specimens. The specimens, containing an 8 mm rebar with varying concrete cover, are first cracked in tension and then immersed in a chloride solution. Multiple scans at different time points are to be conducted to allow for the tracking of the formation of corrosion products and the consequent fracture mechanisms.