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This study introduces a constant water pressure seepage rate detection method to assess the impermeability recovery of cracked concrete using crystalline waterproofing agents. The method focuses on quantifying crack repair effectiveness. Tests involve 100mm cubic C35 concrete specimens with induced micro-cracks under uniaxial compression. Three groups are studied: C-0 (reference), S-1.3 (internally-mixed), and P-1.3 (sprayed). Specimens are repaired and submerged in water at 25°C. Seepage rate tests are conducted at 7d, 14d, 28d, and 56d post-crack formation. Seepage rates decrease over time with repair age, notably declining from 7 - 28 days and stabilizing from 28 - 56 days. Application methods significantly affect impermeability recovery, with C - 0 > P - 1.3 > S - 1.3 consistently in seepage rates. By 56 days, rates are approximately 0.8mm/h for S - 1.3, 4.2mm/h for P - 1.3, and 9.8mm/h for C - 0, indicating better long-term stability and anti-seepage effects for the internal mixing method over spraying. The study demonstrates the seepage rate method’s ability to quantitatively track crack leakage evolution and differentiate the repair effects of crystalline waterproofing agents.

The effect of high temperatures up to 800 °C on the physical and mechanical characteristics and fracturing behaviour of Beishan granite is experimentally studied with a combination of acoustic emission (AE), digital image correlation (DIC) and optical microscope observations. The experimental results show that the responses of the P-wave velocity, the effective porosity, Young’s modulus, and the uniaxial compressive strength (UCS) of the granite to temperature are different. The critical temperature for the brittle–ductile transition of Beishan granite is between 500 and 600 °C. The counts, cumulative energy, b value, and waveform from AE and the full-field deformation evolution from DIC are combined to investigate the damage evolution and fracture mechanism in heated granite. It is found that a rise in temperature increases the number of AE events but reduces the cumulative energy release. Tensile microcracking mainly occurs in granite exposed to low temperatures, while shear fracturing gradually dominates in granite exposed to higher temperatures. With increasing temperature from 25 to 800 °C, the failure mode of granite specimens changes from being controlled by longitudinal splitting cracks to a single shear fracture and finally to multiple conjugate shear fractures. Microscopic observation of granite thin sections is conducted to further reveal the essential mechanism driving the physical–mechanical response and fracturing behaviour of heated Beishan granite.

Cracks and cavities belong to two basic forms of damage to the concrete structure, which may reduce the load-bearing capacity and tightness of the structure and lead to failures and catastrophes in construction structures. Excessive and uncontrolled cracking of the structural element may cause both corrosion and weakening of the adhesion of the reinforcement present in it. Moreover, cracking in the structure negatively affects its aesthetics and in extreme cases may cause discomfort to people staying in such a building. Therefore, the following article provides an in-depth review of issues related to the formation and development of damage and cracking in the structure of concrete composites. It focuses on the causes of crack initiation and characterizes their basic types. An overview of the most commonly used methods for detecting and analyzing the shape of microcracks and diagnosing the trajectory of their propagation is also presented. The types of cracks occurring in concrete composites can be divided according to eight specific criteria. In reinforced concrete elements, macrocracks depend on the type of prevailing loads, whereas microcracks are correlated with their specific case. The analyses conducted show that microcracks are usually rectilinear in shape in tensioned elements; in shear elements there are wing microcracks with straight wings; and torsional stresses cause changes in wing microcrack morphology in that the tips of the wings are twisted. It should be noted that the subject matter of microcracks and cracks in concrete and structures made of this material is important in many respects as it concerns, in a holistic approach, the durability of buildings, the safety of people staying in the buildings, and costs related to possible repairs to damaged structural elements. Therefore, this problem should be further investigated in the field of evaluation of the cracking and fracture processes, both in concrete composites and reinforced concrete structures.

O3-type layered oxide for sodium-ion batteries have attracted significant attention owing to their low cost and high energy density. However, their applications are restricted by rapid capacity decay during long-term cycling, with uneven Na + distribution and microcrack formation being key contributing factors. In this study, a customized reconstruction layer integrating a fast ion conductor NaCaPO 4 coating with gradient Ca 2+ doping is developed to enhance the surface chemical and mechanical stability of the layered cathodes. The gradient Ca 2+ doped interphase facilitates uniform phase transformation within the particles, minimizes lattice mismatch, ensures even Na + distribution, and mitigates microcrack formation through a pinning effect. Consequently, the optimized sample exhibits improved electrochemical performance and robust reliability under high-voltage conditions and a broad temperature range (−10 to 50 °C). The practical feasibility of a pouch-type full cell paired with a hard carbon anode is demonstrated by a high capacity retention of 82.9% after 300 cycles at 0.5 C. This scalable interface modification strategy provides valuable insights into the development of advanced oxide cathode materials for sodium-ion batteries. O3-type layered oxides are promising for sodium-ion batteries but suffer from rapid capacity decay. Here, the authors demonstrate that a NaCaPO 4 -derived gradient Ca 2+ -doped reconstruction layer enhances stability by mitigating phase transition-induced lattice stress and homogenizing Na-ion distribution.

All-solid-state batteries with a Li anode and ceramic electrolyte have the potential to deliver a step change in performance compared with today’s Li-ion batteries 1 , 2 . However, Li dendrites (filaments) form on charging at practical rates and penetrate the ceramic electrolyte, leading to short circuit and cell failure 3 , 4 . Previous models of dendrite penetration have generally focused on a single process for dendrite initiation and propagation, with Li driving the crack at its tip 5 – 9 . Here we show that initiation and propagation are separate processes. Initiation arises from Li deposition into subsurface pores, by means of microcracks that connect the pores to the surface. Once filled, further charging builds pressure in the pores owing to the slow extrusion of Li (viscoplastic flow) back to the surface, leading to cracking. By contrast, dendrite propagation occurs by wedge opening, with Li driving the dry crack from the rear, not the tip. Whereas initiation is determined by the local (microscopic) fracture strength at the grain boundaries, the pore size, pore population density and current density, propagation depends on the (macroscopic) fracture toughness of the ceramic, the length of the Li dendrite (filament) that partially occupies the dry crack, current density, stack pressure and the charge capacity accessed during each cycle. Lower stack pressures suppress propagation, markedly extending the number of cycles before short circuit in cells in which dendrites have initiated. Analysis of dendrite initiation, owing to filling of pores with lithium by means of microcracks, and propagation, caused by wedge opening, shows that there are two separate processes during dendrite failure of lithium metal solid-state batteries.

The paper presents results of tests on the effect of the addition of fly ash (FA) in the amounts of 0%, 20%, and 30% by weight of cement on the interfacial microcracks in concrete composites subjected to dynamic loads. The analyses were carried out based on the results of the microstructural tests using a scanning electron microscope (SEM). The average width of the microcracks (Wc) in the interfacial transition zone (ITZ) of coarse aggregate with cement matrix was evaluated. During the studies beneficial effect of the addition of FA on reduction of the size of Wc in the ITZ of concrete composites under dynamic loading were observed. Based on obtained test results, it was found that using the 20% FA additive causes favorable changes in the microstructure of mature concrete. In this composite, the average value of Wc was lower by more than 40% compared to the result obtained for the reference concrete. In contrast, concrete containing 30% FA additive had greater microcracks in the ITZ area by over 60% compared to the material without additive. In all analyzed composites, an increase in the Wc value by almost 70% to over 110% in the case of occurrence of dynamic loads was also observed. This was the most evident in the case of concrete with a higher content of FA.

Realizing improved strength–ductility synergy in eutectic alloys acting as in situ composite materials remains a challenge in conventional eutectic systems, which is why eutectic high-entropy alloys (EHEAs), a newly-emerging multi-principal-element eutectic category, may offer wider in situ composite possibilities. Here, we use an AlCoCrFeNi 2.1 EHEA to engineer an ultrafine-grained duplex microstructure that deliberately inherits its composite lamellar nature by tailored thermo-mechanical processing to achieve property combinations which are not accessible to previously-reported reinforcement methodologies. The as-prepared samples exhibit hierarchically-structural heterogeneity due to phase decomposition, and the improved mechanical response during deformation is attributed to both a two-hierarchical constraint effect and a self-generated microcrack-arresting mechanism. This work provides a pathway for strengthening eutectic alloys and widens the design toolbox for high-performance materials based upon EHEAs. Producing in situ composite materials with superior strength and ductility has long been a challenge. Here, the authors use lamellar microstructure inherited from casting, rolling, and annealing to produce an ultrafine duplex eutectic high entropy alloy with outstanding properties.

To address the problem of incomplete extraction for microcracks due to low contrast and blurred edges in metal-bearing roller line microcrack images, a detection algorithm for low-contrast line microcracks based on global contrast enhancement and threshold region growth segmentation is proposed. A global contrast enhancement algorithm is constructed by analyzing low-contrast characteristics in metal-bearing roller line microcrack images. Defining a multi-scale Gaussian function for contrast stretching and adjusting contrast parameters to complete contrast enhancement, combined with the metal-bearing roller microcrack edge blurring problem, the seeds are selected according to the gradient criterion. Meanwhile, the region growth of the gray value criterion is designed to complete the extraction for line microcracks. The results show that the metal-bearing roller line microcrack images are enhanced by global contrast. The enhanced images achieve an SSIM value of 0.9590 and a mean error of 0.008. The extraction precision of the metal-bearing roller line microcrack is 98.503%.

To address the insufficient sensitivity of conventional ultrasonic testing techniques in detecting surface microcracks on aircraft skins, this study proposes a micro-damage detection method based on the principle of Coda Wave Interferometry (CWI). By establishing a multi-physics coupled micro-damage scattering model, high-precision extraction and quantitative characterization of coda wave signal features are realized. The results of theoretical analysis and experimental validation reveal that, under the condition of microcracks with varying sizes, the relative wave velocity variation of coda wave signals exhibits a significant linear correlation with damage dimensions. Through the establishment of such a mapping relationship, this method breaks through the near-surface resolution limitation of traditional ultrasonic testing techniques and enables quantitative detection of submillimeter/micrometer-scale surface microcracks.

The inherent quasi-brittleness of cement-based materials, due to the disorder of their hydration products and pore structures, present significant challenges for directional matrix toughening. In this work, a rigid layered skeleton of cement slurry was prepared using a simplified ice-template method, and subsequently flexible polyvinyl alcohol hydrogel was introduced into the unidirectional pores between neighboring cement platelets, resulting in the formation of a multi-layered cement-based composite. A toughness improvement of over 175 times is achieved by the implantation of such hard-soft alternatively layered microstructure. The toughening mechanism is the stretching of hydrogels at the nano-scale and deflections of micro-cracks at the interfaces, which avoid stress concentration and dissipate huge energy. Furthermore, this cement-hydrogel composite also exhibits a low thermal conductivity (around 1/10 of normal cement) and density, high specific strength and self-healing properties, which can be used in thermal insulation, seismic high-rise buildings and long-span bridges. Despite widely used in the construction sector, Portland cement’s high brittleness and low toughness still pose challenges in some applications. Here, authors apply an ice-templating method to fabricate a cement-hydrogel composite with alternating layered microstructure resulting in significantly increased toughness.