Search Results (86)

Normal concrete exhibits poor resistance to chloride penetration, often leading to reinforcement corrosion and premature structural failure. In contrast, ultra-high-performance concrete (UHPC) demonstrates superior resistance to corrosion caused by chloride salts. The chloride diffusion behaviour of UHPC was investigated via long-term immersion (LTI) and rapid chloride migration (RCM) tests. Additionally, this study presents the first development of a time-dependent diffusion model for UHPC under chloride corrosion, as well as the proposal of a performance-based design method for calculating the protective layer thickness. Results show that the incorporation of steel fibers reduced the chloride diffusion coefficient ($D$) by 37.9%. The free chloride content (FCC) in UHPC increased by 92.0% at 2 mm after 300 d of the action of LTI. $D$ decreased by up to 91.0%, whereas the surface chloride concentration ($C_{\mathrm{s}}$) increased by up to 92.5% under the action of LTI. The time-dependent models of $D$ and $C_{\mathrm{s}}$ followed power and logarithmic functions, respectively. An increase in UHPC surface temperature, relative humidity, and tensile stress ratio significantly diminishes the chloride resistance of UHPC. The minimum UHPC protective layer thicknesses required for UHPC-HPC composite beams with design service lives of 100 years, 150 years, and 200 years are 30 mm, 37 mm, and 43 mm, respectively. Full article

In high-humidity environments, the epoxy resin solid insulation materials of high-frequency transformers are prone to aging, resulting in varying degrees of deterioration in the material’s dielectric properties and other aspects. To enhance the adaptability of epoxy resin in high humidity environments, this paper, based on the molecular dynamics simulation method, establishes epoxy resin-based nanocomposites with doped nanofillers: a pure epoxy resin model and three epoxy resin models, respectively, doped with carbon nanotubes, graphene(GR), and SiO₂. Based on the above models, using LAMMPS-17Apr2024, the thermal diffusion coefficients (thermal conductivity and specific heat capacity), glass transition temperatures, and dielectric constants under different moisture contents are calculated. The results show that the various properties of the epoxy resin nanocomposites doped with nanofillers have been improved to varying degrees. Among them, the GR/epoxy resin composite model shows the most significant improvements in thermal conductivity, thermal diffusivity, and glass transition temperature, and the SiO₂/epoxy resin composite model has the best dielectric properties. Considering the high-temperature operation conditions and heat dissipation requirements of the high-frequency transformer, the GR-enhanced epoxy resin becomes the optimal filler choice. Full article

This study investigates a UDETA-modified polyurethane–urea (PUU) self-healing coating for wind turbine blades, focusing on its ability to autonomously repair surface erosion damage under realistic environmental conditions. A multiphysics finite element model was developed to couple temperature, moisture, and stress effects on crack healing, and a Gaussian process regression (GPR) model was trained on 35 experimental data points to predict the mobile fraction and healing thresholds with high accuracy (R² = 0.79, MAE = 0.059). The diffusion coefficient of water in the PUU matrix was determined as 11.03 × 10⁻⁷ mm²/s, and stress-driven moisture accumulation at crack tips was shown to accelerate crack healing. Erichsen cupping test simulations were conducted to reproduce experimental crack patterns, demonstrating brittle behavior in dehydrated coatings with a Young’s modulus of 50 MPa and critical principal strains of 0.48. An exponential healing function was incorporated into the computational model and validated against experiments, predicting significant crack healing within 24 h of humidity exposure. These findings provide quantitative design criteria for self-healing coatings, enabling the selection of UDETA content, thickness, and curing strategies to extend wind turbine blade service life while reducing maintenance costs. Full article

Moisture in porous building materials significantly affects all their technical parameters. For this reason, it is important to accurately determine coefficients that describe moisture transport inside these materials. The main parameters concerning the hygroscopic range are as follows: water vapor permeability δ, water vapor resistance factor μ, and water vapor diffusion coefficient D. Autoclaved aerated concrete (AAC), one of the most popular materials used for the construction of external walls, was tested. The study focused on the four density classes: 400, 500, 600, and 700. Using a modified cup method, measurements of the corresponding coefficients δ, μ, D were carried out in six ranges of relative air humidity: 11–30, 30–54, 54–60, 60–75, 75–85, 85–98%. The results prove that not only the level of humidity tested, but also the structure within the same material group has a significant impact on all parameters, strongly differentiating their values. In this regard, precise numerical simulations concerning moisture transport processes in autoclaved aerated concrete must take into account both its density class and the moisture range in which these processes occur. Full article

Energy recovery ventilators are essential for reducing building energy consumption, with the dynamic variation in their efficiency being a significant area of current research. To quickly analyze the parameters affecting the dynamic changes in energy recovery efficiency, this study develops a mathematical model for heat and moisture transfer. The model was validated through computational fluid dynamics (CFD) simulations and experimental data. The validation results showed that the discrepancies between the model’s sensible heat and enthalpy efficiencies and the experimental data were approximately 4%, while the error range for sensible heat efficiency compared to CFD simulations was between 3% and 7%. This model was used to evaluate various factors affecting energy recovery efficiency. The findings show that outdoor temperature and relative humidity have little effect on sensible heat efficiency, whereas latent heat efficiency increases with rising outdoor temperature and humidity. Both sensible and latent heat efficiency improve as airflow decreases, with latent heat efficiency being more sensitive to changes in airflow. Additionally, due to the very thin heat exchanger membrane, the mass diffusion coefficient has a more significant effect on efficiency than the thermal conductivity coefficient. In conclusion, energy recovery efficiency is dynamic, and the proposed model provides rapid predictions of how influencing factors affect the efficiency. Full article

Concrete coating technology is a key measure that enhances the durability of concrete structures. This paper systematically studies the performance, applicability, and impact of different types of anti-corrosion coatings on concrete durability, focusing on their resistance to chloride ion penetration, freeze–thaw cycles, carbonation, and sulfate corrosion. The applicability of existing testing methods and standard systems is also evaluated. This study shows that surface-film-forming coatings can create a dense barrier, reducing chloride ion diffusion coefficients by more than 50%, making them suitable for humid and high-chloride environments. Pore-sealing coatings fill capillary pores, improving the concrete’s impermeability and making them ideal for highly corrosive environments. Penetrating hydrophobic coatings form a water-repellent layer, reducing water absorption by over 75%, which is particularly beneficial for coastal and underwater concrete structures. Additionally, composite coating technology is becoming a key approach to addressing multi-environment adaptability challenges. Experimental results have indicated that combining penetrating hydrophobic coatings with surface-film-forming coatings can enhance concrete’s resistance to chloride ion penetration while ensuring weather resistance and wear resistance. However, this study also reveals that there are several challenges in the standardization, engineering application, and long-term performance assessment of coating technology. The lack of globally unified testing standards leads to difficulties in comparing the results obtained from different test methods, affecting the practical application of these coatings in engineering. Moreover, construction quality control and long-term service performance monitoring remain weak points in their use in engineering applications. Some engineering case studies indicate that coating failures are often related to an insufficient coating thickness, improper interface treatment, or lack of maintenance. To further improve the effectiveness and long-term durability of coatings, future research should focus on the following aspects: (1) developing intelligent coating materials with self-healing, high-temperature resistance, and chemical corrosion resistance capabilities; (2) optimizing multilayer composite coating system designs to enhance the synergistic protective capabilities of different coatings; and (3) promoting the creation of global concrete coating testing standards and establishing adaptability testing methods for various environments. This study provides theoretical support for the optimization and standardization of concrete coating technology, contributing to the durability and long-term service safety of infrastructure. Full article

This study aims to evaluate the drying performance of a multi-stage solar-assisted heat pump drying system for tomatoes. The method involves theoretical calculations based on the optimal drying process and experimental investigations to assess the impact of different drying temperatures and relative humidity on drying characteristics. The results from the theoretical calculations reveal that the multi-stage solar-assisted heat pump drying system outperforms a single-stage system, particularly under lower ambient temperatures or higher fresh air volumes. In spring/autumn, with 25% fresh air, solar energy accounts for 85.12% of the total energy consumption, achieving a performance coefficient of 39.16, a moisture extraction rate of 40.7 kg/kWh, and energy consumption of 0.02 kWh/kg. Carbon dioxide emissions amount to 10.45 kg/year, with a net reduction of 7.88 kg/year. The experimental results indicate that higher relative humidity increases drying time and reduces the diffusion coefficient, which results in higher material temperatures and greater nutrient loss. The optimal drying process is achieved at 70 °C and 20% relative humidity. In conclusion, the multi-stage solar-assisted heat pump drying system demonstrates superior performance in energy efficiency and sustainability compared to single-stage systems. The optimal drying conditions for tomatoes are identified, and the findings contribute to improving drying processes in food preservation while minimizing environmental impact. Full article

This paper studies the effect of specimen size on the moisture uptake characteristics of pultruded E-glass/vinylester composites exposed to conditions of immersion and 99% RH over a range of temperatures. Four different specimen sizes representative of sizes commonly used for material characterization (tension, short-beam-shear, and dynamic mechanical thermal analysis) as well as moisture uptake are included. It is shown that both exposure conditions and geometry significantly influence uptake behavior, and that the differences, in general, can be elucidated through consideration of surface-to-edge area ratios of the specimens. For the current study, the ratio extends from 2.528 at the lowest level for the short-beam-shear specimens to 16.979 at the highest for the tensile specimens. The overall levels of uptake in the period of exposure, the levels of transition uptake, and the diffusion coefficients are noted to increase with a decrease in the ratio, suggesting an increased influence of the edge effect, which is further enhanced with an increase in temperature. Levels of normalized transition uptake for the specimens with the lowest surface-to-edge area ratio are 12.5 and 8.2 times higher than those for the specimens with the highest ratio at the two extreme temperatures, respectively, when exposed to 99% RH, and are 7.2 and 15.3 times, respectively, under conditions of immersion. Activation energy calculations also highlight differences based on specimen size and the condition of exposure with immersion leading to a lower activation energy than exposure to 99% RH when considering the initial linear regime with the specimens having the largest surface-to-edge area ratios showing 11.3–13.5% higher levels due to exposure to 99% RH, whereas the two specimens with the smaller ratios show a 4.9% increase. The findings highlight the importance of specimen size and exposure conditions and emphasize that the commonly used assumptions could lead to inaccurate results especially when extrapolated. The use of the immersion condition as a means of accelerating field conditions of humidity could significantly overestimate effects. Further, the direct use of uptake characteristics from specimens at one size, or surface-to-edge area ratio, could lead to inaccurate conclusions if extrapolated to specimens that are significantly different leading to design and durability prediction implications. Full article

Deep drawing is a common process for shaping paperboard packages. To improve performance, the paperboard is kept in a room with high humidity before treatment. The surfaces of forming tools that come into contact with the paperboard are heated. A control problem for heating moist paperboard, with evaporation from the pore surface, is considered in this paper. Micro-CT images of three different paperboards are taken, segmented, and parameterized with respect to the specific pore surface in terms of the pore surface per pore volume, pore volume fraction, fiber thickness, average surface contact area between fibers, and unsupported fiber length. Simple averaging formulas are provided to compute the effective coefficients in the coupled water-diffusion and heat-transfer problem with a phase transition. The model is validated by experimental measurements and offers an opportunity for optimal heating control to simultaneously ensure compliance of the paperboard layer, leading to small delamination at its boundary, thereby avoiding folding. Full article

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0–62.9 W/m²∙K and 0.007–0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10⁻¹⁰–8.5 × 10⁻¹⁰ m²/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data ($R^2\ge$ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process. Full article

Geographic patterns determine geogenic radon factors that, changing over the territory, form spatial structures of different scales associated with regional and local variations. The study of these structures is important for assessing the possibility of using limited data to predict geogenic radon potential. Our research focuses on the study of the physical properties of soils (moisture, soil density, porosity and void ratio) in the Kuznetsk coal basin. Their variations are studied using statistical methods, a variogram cloud and spatial autocorrelation of data. Soil moisture and porosity have the greatest variability in space and with depth. We conclude that the assessment of geogenic radon predictors requires consideration of the variation coefficient and autocorrelation indices at different scales. Based on the variability of humidity and the fairly homogeneous nature of the studied soils (loams), to assess the radon hazard, it is necessary to study the influence of climatic conditions, since the permeability of the environment for radon will be determined by soil moisture. With the predominance of substantially clayey soils, it is necessary to study the content of ²²⁶Ra in the upper horizons, since it is assumed that radon is predominantly diffusely transferred, in which its role is dominant. Full article

The moisture transfer coefficient is a key parameter for analyzing the moisture-based physical properties of materials and studying the heat–moisture coupling process within building envelopes. The liquid-water transfer coefficient, as an important aspect of this process, plays a significant role, especially under high-humidity conditions. However, the global research on liquid-water transfer coefficients is still far from complete. To further enhance the research on liquid-water transfer coefficients, this study conducted capillary water absorption experiments on seven traditional and new porous building materials, focusing on testing the moisture transfer coefficients, primarily the liquid-water transfer coefficient. A novel analysis regarding the impact of sealing materials was proposed, based on the experimental results. Based on the experimental data, the concept of a critical value related to the variation in the capillary moisture content and the liquid-water diffusion coefficient was raised, and, building upon traditional empirical models, a completely new computational model was proposed. Data processing was carried out using methods such as variability analysis, correlation analysis, and nonlinear regression for model fitting. The research findings indicate the following: (1) The capillary water absorption rate and capacity of a material are influenced by its density and porosity. (2) In terms of sealing materials, self-adhesive films performed better than non-adhesive films. (3) The concept of critical capillary moisture content was proposed, based on the rate of change in the liquid-water diffusion coefficient. For the threshold of $w$ ≤ 80%, a new calculation model with a higher correlation coefficient was proposed which can meet the calculation requirements of the diffusion coefficient under the vast majority of relative-humidity conditions. Full article

Goat meat has a high nutritional value, since it contains up to 29% protein, as well as iron, potassium and vitamin B12. To prolong the shelf life of this food, a drying process can be applied; however, there is scarce information on the kinetics and drying parameters for this food material. The objective of this work was to characterize the thermal drying process of goat meat, through the mathematical modeling of convective drying kinetics, and its validation with experimental data obtained in a drying tunnel. The experiments were carried out with samples of loin (Longissumus dorsi) of Boer goat meat from the Mixteca region of Oaxaca (Mexico). Meat samples were subjected to air convection drying at 40, 50, 60 and 70 °C (with temperature oscillation), with air velocities of 1 and 2 m/s. Drying kinetics, air and meat temperature profiles, relative humidity and air flow velocity were recorded. Four models were analyzed: two-term, Midilli’s model, Wang and Singh’s model and a heuristic model with temperature dependence. The proposed mathematical models represented drying kinetics with an accurate fitting of experimental data, with standard errors (RMSE) in the range of 0.004–0.029. The estimated diffusion coefficients are consistent with the transport properties in biomaterials. The heuristic model was based on the solution of the effective diffusion equation considering the linearization of the temperature-dependent diffusion coefficient, showing a standard error in the range of 0.007–0.028, satisfactorily representing the temperature oscillations that allows a moisture diffusion reorganization, mainly when drastic temperature changes occur. Full article

Truffles of the Tuber genus (Pezizales, Ascomycetes) are among the most valuable and expensive foods, but their shelf life is limited to 7–10 days when stored at 4 °C. Alternative preservation methods have been proposed to extend their shelf life, though they may alter certain quality parameters. Recently, a hypogeal display case equipped with an ultrasonic humidity system (HDC) was developed, extending the shelf life to 2–3 weeks, depending on the truffle species. This study assesses the efficacy of HDC in preserving Tuber melanosporum and Tuber borchii ascomata over 16 days, using quantitative magnetic resonance imaging (QMRI) to monitor water content and other parameters. Sixteen T. melanosporum and six T. borchii ascomata were stored at 4 °C in an HDC or a static fridge (SF) as controls. QMRI confirmed that T. borchii has a shorter shelf life than T. melanosporum under all conditions. HDC reduced the rate of shrinkage, water, and mass loss in both species. Additionally, the Apparent Diffusion Coefficient (ADC), longitudinal relaxation time (T1), and transverse relaxation time (T2), which reflect molecular changes, decreased more slowly in HDC than SF. QMRI proves useful for studying water-rich samples and assessing truffle preservation technologies. Further optimization of this method for industrial use is needed. Full article

Climate change poses a significant threat to the durability of reinforced concrete (RC) bridges, which are particularly vulnerable to chloride-induced corrosion of steel reinforcements. The main problem for the current research is the increase in the projected maximum temperature values, especially for the high emission scenario in the future because of climate change, applied to the upper part of the RC bridge deck made of geopolymer concrete (GPC) composed of 50% fly ash and 50% slag. This will reduce the corrosion initiation time and the safety and durability of the RC bridge deck structure. Despite extensive research on chloride-induced corrosion, there is a scientific gap in understanding how future climate variations will influence the rate of corrosion in RC bridges. Specifically, comprehensive studies assessing the effect of maximum temperature on the probability of the corrosion initiation process in RC bridge decks made of GPC exposed to chloride environments are lacking. This study used the Monte Carlo simulation method to assess the probability of corrosion initiation (PCI) under various future climate scenarios for Toronto City, Canada. This research examines the impact of the maximum temperature and relative humidity on the diffusion coefficient of chloride ions in concrete. It assesses the PCI for different concrete cover thicknesses in RC decks made of geopolymer concrete composed of 50% fly ash and 50% slag over specified periods, dealing with the sensitivity analysis for this parameter among different parameters defined in the performance function. The results indicate a substantial increase in the PCI for a 40 mm concrete cover compared with a 50 mm cover in various years. Furthermore, maximum temperatures ranging from 40 °C to 45 °C significantly increase the PCI compared with temperatures between 25 °C and 35 °C for a 50 mm concrete cover. Finally, polynomial functions have been deduced to investigate the reliability index and PCI as a function of various coefficients of variations for mean concrete covers made of GPC at various maximum temperature values in different years. These findings provide important information for the design and maintenance of RC structures, ensuring their longevity in the face of climate change. Full article