Search Results (20)

High-temperature vulcanized silicone rubber (HTV-SR), widely used in composite insulators, experiences performance degradation when subjected to combined stresses such as corona discharge, humidity and temperature fluctuations. This degradation poses significant risks to the reliability of power grid operation. To investigate the aging behavior and mechanisms of HTV-SR under the combined influences of corona, moisture and thermal cycling, a series of multi-factor accelerated aging tests are conducted. Comprehensive characterizations of surface morphology, structural, mechanical and electrical properties are performed before and after aging. The results reveal that corona discharge induces molecular chain scission and promotes oxidative crosslinking, leading to surface degradation. Increased humidity accelerates water diffusion and hydrolysis, enhancing crosslink density but reducing material flexibility, thereby further deteriorating structural integrity and electrical performance. Compared with constant temperature aging, thermal cycling introduces repetitive thermal stress, which significantly aggravates filler migration and leads to more severe mechanical and dielectric degradation. These findings elucidate the multi-scale degradation mechanisms of HTV-SR under the coupling effects of corona discharge, humidity and temperature cycling, providing theoretical support for the design of corona- and humidity-resistant silicone rubber for composite insulator applications. Full article

Global cement manufacturing generated 1.6 billion metric tons of CO₂ in 2022 and relies heavily on non-renewable raw materials. Utilizing agro-industrial waste as supplementary cementitious material (SCM) can help mitigate the demand for these resources. SCMs have been integrated into cement production to deliver both technical and environmental benefits to mortars and concrete. This study examines mortar blends containing blast furnace slag (BFS), Brazilian calcined clay (BCC), and bamboo leaf ash (BLA). While BFS and BCC are already established in the cement industry, recent research has highlighted BLA as a promising pozzolanic material. The SCMs were characterized, and mortars were produced to assess their flexural and compressive strength, as well as durability indicators such as electrical resistivity, chloride diffusion, migration coefficient, and carbonation resistance. The findings reveal significant performance enhancements. Partial cement replacement (20% and 40%) maintained the strength of both binary and ternary mortars, demonstrating statistical equivalence to the reference mortar (p > 0.05). It also contributed to an improved pore structure, reducing the migration coefficient by up to four times in the 20BLA20BCC mix (which replaces 20% of cement with BLA and 20% with BCC) compared to the reference mix. Chemically, the SCMs enhanced the chloride-binding capacity of the cementitious matrix by up to seven times in the case of the 20BCC mortar, thereby improving its durability. Therefore, all tested compositions—binary and ternary—showed mechanical and durability advantages over the reference while also contributing to the reduction in environmental impacts associated with the cement industry. Full article

The composite performance of steel fiber-reinforced concrete (SFRC) is excellent, and its application potential in subsea tunnel engineering has gradually emerged. This paper discusses three types of laboratory testing methods for studying the corrosion of SFRC induced by chlorides: the ion diffusion method, electric field migration method, and pre-corrosion method. The similar relationship between short-term accelerated deterioration tests and the natural corrosion process, as well as the experimental setup for simulating the coupling effect of multiple factors, requires further exploration. Furthermore, the mechanisms of steel fibers influencing the chloride corrosion resistance of SFRC are explored from four aspects: type, coating, shape, and dosage. Finally, by examining practical case studies of SFRC in subsea tunnel applications, the challenges posed by the multi-directionality of chloride ion corrosion, the diversity of corrosion sources, and the uneven distribution of steel fibers are highlighted. Future research should focus on enhancing the application of SFRC in subsea tunnel linings. This study provides a reference and basis for promoting the application of SFRC in subsea tunnel engineering and indicates future development directions. Full article

The widespread adoption of geopolymer concretes in the industry has been slow, mainly due to concerns over their long-term performance and durability. One of the main causes of concrete structures’ deterioration is chloride-induced corrosion of the reinforcement. The reinforcement corrosion process in concrete is composed of two main stages: the initiation phase, which is the amount of time required for chloride ions to reach the reinforcement, and the propagation phase, which is the active phase of corrosion. The inherent complexities associated with the properties of precursors and type of activators, and with the multi-physics processes, in which different transfer mechanisms (moisture, chloride, oxygen, and charge transfer) are involved and interact with each other, have been a major obstacle to predicting the durability of reinforced alkali-activated concretes in chloride environments. Alternatively, the durability of alkali-activated concretes can be assessed through testing. However, the performance-based tests that are currently available, such as the rapid chloride permeability test, the migration test or the bulk diffusion test, are only focusing on the initiation phase of the corrosion process. As a result, existing testing protocols do not capture every aspect of the material performance, which could potentially lead to misleading conclusions, particularly when involving an electrical potential to reduce the testing time. In this paper, a new performance-based test is proposed for assessing the performance of alkali-activated concretes in chloride environments, accounting for both the initiation and propagation phases of the corrosion process. The test is designed to be simple and to be completed within a reasonable time without involving any electrical potential. Full article

The research on and application of electric fields to promote the rapid infiltration of ions into cement concrete have been widely explored. Still, there are few studies on the migration of sulfate ions using electric fields. In this paper, a new test method is designed using the principle of electric fields, that is, to accelerate the attack of sulfate into concrete under the action of the electric field, to test the resistance of concrete to sulfate attack. By testing different water–cement ratios, different pulse frequencies, different ages, and different soaking environments, the influence of the electric field on the sulfate resistance of concrete was analyzed. The results show that the compressive strength of concrete in a sulfate attack environment is smaller than that of conventional attack and water immersion environment when the water–cement ratio is 0.3, 0.4, and 0.5 under the action of the electric field and increases with the increase of water in the water–cement ratio. Compared with a 14 day test, the compressive strength of concrete in a sulfate attack environment decreased by 1.9%, 8.6%, and 2.9%, respectively, at 28 days, which was faster than that of conventional attack and water immersion. The compressive strength of the concrete in the sulfate attack environment during the full immersion test and the semi-immersion test is smaller than that of the conventional attack and water immersion, and the semi-immersion test method is more obvious than the full immersion test method. The microscopic morphology of the test group, the water group, and the solution group were compared. From the microscopic morphology comparison, it can be seen that the electric field accelerates the diffusion of sulfate ions into the cement concrete and accelerates the reaction of sulfate ions with the relevant components in the cement concrete. Given the demand for concrete to resist sulfate attack under the action of the electric field, developing new and efficient protective materials is an important research direction. At present, the market lacks protective materials specifically for such an attack environment. This paper provides the theoretical basis and technical support for improving the effectiveness of concrete surface protection technology and engineering practices. Full article

The lithium metal battery is likely to become the main power source for the future development of flying electric vehicles for its ultra-high theoretical specific capacity. In an attempt to study macroscopic battery performance and microscopic lithium deposition under different pressure conditions, we first conduct a pressure cycling test proving that amplifying the initial preload can delay the battery failure stage, and the scanning electron microscope (SEM) shows that the pressure is effective in improving the electrode’s surface structure. Secondly, we analyze how differing pressure conditions affect the topography of lithium deposits by coupling the nonlinear phase-field model with the force model. The results show that the gradual increase in the external pressure is accompanied by a drop in the length of the dendrite and the migration curvature in the diaphragm, and the deposition morphology is gradually geared towards smooth and thick development, which can significantly reduce the specific surface area of lithium dendrite. However, as cyclic charging and discharging continue, the decrease in the electrolyte diffusion coefficient results in higher internal stress inside the battery, and thus the external pressure must be increased so as to achieve marked inhibitory effects on the growth of the lithium dendrite. Full article

Mine tailings have shown viability as the fine–grained layer in a capillary barrier structure for controlling acid mine drainage in a circular economy. Their saturated hydraulic conductivities (k_sat) under wetting–drying cycles and freeze–thaw cycles remain unexplored. In this study, modified tailings with a weight ratio of 95:5 (tailings/hydrodesulfurization (HDS) clay from waste–water treatment) and an initial water content of 12% were used. The k_sat of specimens was measured after up to 15 wetting–drying cycles, each lasting 24 h, with a drying temperature of 105 °C. The k_sat for wetting–drying cycles decreased from 3.9 × 10⁻⁶ m/s to 9.5 × 10⁻⁷ m/s in the first three cycles and then stabilized in the subsequent wetting–drying cycles (i.e., 5.7 × 10⁻⁷ m/s–6.3 × 10⁻⁷ m/s). Increased fine particles due to particle breakage are the primary mechanism for the k_sat trend. In addition, the migration of fines and their preferential deposition near the pore throat area may also promote this decreasing trend through the shrinking and potentially clogging–up of pore throats. This could be explained by the movement of the meniscus, increased salinity, and, subsequently, the shrinkage of the electrical diffuse layer during the drying cycle. Similar specimens were tested to measure k_sat under up to 15 freeze–thaw cycles with temperatures circling between −20 °C and 20 °C at 12 h intervals. Compared to the untreated specimen (i.e., 3.8 × 10⁻⁶ m/s), the k_sat after three freeze–thaw cycles decreased by 77.6% (i.e., 8.5 × 10⁻⁷ m/s) and then remained almost unchanged (i.e., 5.6 × 10⁻⁷ m/s–8.9 × 10⁻⁷ m/s) in subsequent freeze–thaw cycles. The increased fine grain content (i.e., 3.1%) can be used to explain the decreased k_sat trend. Moreover, the migration of fines toward the pore throat area, driven by the advancing and receding of ice lens fronts and subsequent deposition at the pore throat, may also contribute to this trend. Full article

To increase the durability of concrete structures, surface coating is widely used as a preventive maintenance strategy against de-icing salts. We investigated the effectiveness of a small amount of surface penetrant for chloride-induced corrosion on concrete structures exposed to low NaCl concentrations. The diffusion coefficient of mortar specimens with and without coating was determined using the electric migration test. The results indicated that even a small amount of Silane-based penetrant was effective against chloride ion penetration. Full article

This study presents a comparison of the protective properties of three concretes of similar composition on the effect of chloride ions. To determine these properties, the values of the diffusion and migration coefficients of chloride ions in concrete were determined using both standard methods and the thermodynamic ion migration model. We tested a comprehensive method for checking the protective properties of concrete against chlorides. This method can not only be used in various concretes, even those with only small differences in composition, but also in concretes with various types of admixtures and additives, such as PVA fibers. The research was carried out to address the needs of a manufacturer of prefabricated concrete foundations. The aim was to find a cheap and effective method of sealing the concrete produced by the manufacturer in order to carry out projects in coastal areas. Earlier diffusion studies showed good performance when replacing ordinary CEM I cement with metallurgical cement. The corrosion rates of the reinforcing steel in these concretes were also compared using the following electrochemical methods: linear polarization and impedance spectroscopy. The porosities of these concretes, determined using X-ray computed tomography for pore-related characterization, were also compared. Changes in the phase composition of corrosion products occurring in the steel–concrete contact zone were compared using scanning electron microscopy with a micro-area chemical analysis capability, in addition to X-ray microdiffraction, to study the microstructure changes. Concrete with CEM III cement was the most resistant to chloride ingress and therefore provided the longest period of protection against chloride-initiated corrosion. The least resistant was concrete with CEM I, for which, after two 7-day cycles of chloride migration in the electric field, steel corrosion started. The additional use of a sealing admixture can cause a local increase in the volume of pores in the concrete, and at the same time, a local weakening of the concrete structure. Concrete with CEM I was characterized as having the highest porosity at 140.537 pores, whereas concrete with CEM III (characterized by lower porosity) had 123.015 pores. Concrete with sealing admixture, with the same open porosity, had the highest number of pores, at 174.880. According to the findings of this study, and using a computed tomography method, concrete with CEM III showed the most uniform distribution of pores of different volumes, and had the lowest total number of pores. Full article

Polyvinyl chloride (PVC) gels have recently been found to exhibit mechanoelectrical transduction or sensing capabilities under compressive loading applications. This phenomenon is not wholly understood but has been characterized as an adsorption-like phenomena under varying amounts and types of plasticizers. A different polymer lattice structure has also been tested, thermoplastic polyurethane, which showed similar sensing characteristics. This study examines mechanical and electrical properties of these gel sensors and proposes a mathematical framework of the underlying mechanisms of mechanoelectrical transduction. COMSOL Multiphysics is used to show solid mechanics characteristics, electrostatic properties, and transport of interstitial plasticizer under compressive loading applications. The solid mechanics takes a continuum mechanics approach and includes a highly compressive Storakers material model for compressive loading applications. The electrostatics and transport properties include charge conservation and a Langmuir adsorption migration model with variable diffusion properties based on plasticizer properties. Results show both plasticizer concentration gradient as well as expected voltage response under varying amounts and types of plasticizers. Experimental work is also completed to show agreeance with the modeling results. Full article

The kaolinite content is principally responsible for the durability performance of Limestone Calcined Clay Cement (LC3), which calls into question its global applicability. The clay supply has a significant impact on the LC3 system’s reduced carbon footprint advantage. The influence of kaolinite concentration from two separate clays (collected in East South-East Europe) on the durability performance of concrete was investigated in this study. The low-kaolinitic clay had 18% kaolinite, while the medium-kaolinitic clay contained around 41% kaolinite. The compressive strength, chloride intrusion, electrical conductivity, surface resistivity, and sorptivity index were measured on concrete after 28 days. Furthermore, the pore structure development of these mixtures was investigated in relation to the kaolinite content of the mixtures. The reactivity test was performed on clays to measure their reactivity levels within the cementitious system. The results show that kaolinite content has a moderate effect on compressive strength, but it has a considerable effect on other durability indices. When compared to the Portland cement mixture, the chloride migration and diffusion coefficients were reduced by 50% and 36%, respectively, in the combination with a medium kaolinite content (more than 40%). The low-kaolinitic clay, on the other hand, achieved 60% of the chloride penetration resistance of the medium-kaolinitic clay. Furthermore, low-kaolinitic clay has been demonstrated to be suitable for low-carbon concrete in moderate exposure conditions. Full article

Chloride penetration resistance is one of the most important performance measures for the evaluation of the durability of concrete under a chloride environment. Due to differences in theory and experimental conditions, the durability index (chloride diffusion coefficient) obtained from laboratory accelerated migration tests cannot reflect the real process of chloride ingress into concrete in the natural environment. The difference in test methods must be considered and the transfer parameter $k_t$ should be introduced into the service life prediction model when the test results of accelerated methods are used. According to the test data of coastal exposure in South China, the attenuation rule of the chloride diffusion coefficient of different cement-based materials changed with time and was analyzed in this paper. Based on the diffusion coefficient–time curve, the theoretical natural diffusion coefficients of 28 d and 56 d were deduced, which were compared with the chloride diffusion coefficients obtained from the non-steady-state rapid migration method (RCM) at the same age. Therefore, the transfer parameter $k_t$ that expounds the relationship between concrete resistance to chloride permeability under a non-stationary electrical accelerated state and natural diffusion in the marine environment can be calculated; thus, the RCM testing index can be used to evaluate the long-term performance of the concrete structure in the marine environment. The results show that the value of $k_t$ was related to environmental conditions, test methods, and binder systems. Full article

The article presents an oil moistening method, identical to the oil moistening in power transformers. Moistening took place through the migration of moisture from the moistened pressboard to the brand new oil. The AC electrical parameters (admittance, phase shift angle, permittivity, loss tangent and conductivity) of the brand new and moistened insulating oil were tested. All measured parameters were found to be affected by the oil moistening. The greatest changes were observed in the loss tangent and conductivity. Moisturization increases the value of tanδ at a frequency of 10⁻⁴ Hz from about 20 to about 70. With an increase in frequency to about 400–1000 Hz, a minimum is observed, the position of which depends on the temperature. Its value for moistened oil is about six times lower than for brand new oil. This moisturizing increased the activation energy of the conductivity from 0.466 ± 0.0265 eV to 0.890 ± 0.0115 eV. This is likely due to the acceleration of water molecules diffusion from the pressboard into the oil with increasing temperatures. The observed changes in the oil parameters caused by moistening should be taken into account while analyzing the power transformers insulation condition using the FDS method. Full article

With the maturation of silicon-based technologies, silicon solar cells have achieved a high conversion efficiency that approaches the theoretical limit. Currently, great efforts are being made to enhance the reliability of silicon solar cells. When the silicon solar cells are made into modules, potential-induced-degradation (PID) occurs during operation because of the high voltage applied between the frame and the cells, which reduces the efficiency and output power. The diffusion of Na⁺ ions from the front glass and the increased leakage current along the migration path are the major causes of PID. In this work, atomic layer deposition (ALD)-grown amorphous thin Al₂O₃ layers are introduced underneath the front glass to prevent the diffusion of Na⁺ ions and the resulting PID. Accelerated PID tests showed that an ALD-grown Al₂O₃ layer of 30 nm could effectively suppress PID seriously affecting the conversion efficiency or light transmittance. The introduction of an ion-diffusion barrier underneath the front glass is expected to contribute to securing the long-term reliability of silicon-based electricity generation, together with the introduction of barrier layers inside the solar cells. Full article

During the development of a carbon-reinforced mortar interlayer for bridges, the idea of an electrochemical chloride barrier arose. An electrical field is generated between two carbon meshes, and the negatively charged chloride ions are held on the polarized upper carbon mesh to prevent chloride-induced corrosion in the reinforcement. Laboratory tests unexpectedly showed that higher voltages lead to an increase in chloride ions for certain depths of the reference probes. This paper discusses the implementation of analytical and numerical models that finally explain the effect only by the acting diffusion and migration with the help of a finite differences model and finite elements simulations. The effect of the local minimum is limited to positions above the depth of the first carbon layer of the test specimens. It is caused by the lines of the electrical field between the first and second carbon layer. According to the experimental and finite elements simulation results, higher voltages lead to lower chloride concentrations for all positions below the first carbon layer only after sufficient time duration. Therefore, the intended effect of an electrochemical chloride barrier can in general only be observed and confirmed after a certain time depending on position, conditions and parameters. Full article