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Plant fiber reinforced polymer matrix composites have attracted much attention in many industries due to their abundant resources, low cost, biodegradability, and lightweight properties. Compared with synthetic fibers, various plant fibers are easy to obtain and have different characteristics, making them a substitute for synthetic fiber composite materials. However, the aging phenomenon of composite materials has been a key issue that hinders development. In natural environments, moisture absorption performance leads to serious degradation of the mechanical properties of composite materials, which delays the use of composite materials in humid environments. Therefore, the effects of moisture absorption performance of plant fiber composite materials on their mechanical properties have been summarized in this article, as well as various treatment methods to reduce the water absorption of composite materials.

Studies were carried out to find a relation between the important physical property, i.e., water absorption and the main mechanical parameter, i.e., compressive strength (fcm), of concretes containing coal fly ash (CFA) in the amounts of 0% (CFA-00), 20% (CFA-20%), and 30% (CFA-30). The methodology of the water absorption tests reflected the conditions prevailing in the case of reinforced concrete structures operating below the water table. The microstructure of all materials was also assessed. Based on the conducted studies, it was found that both the fcm of concretes with the addition of CFA and its water absorption depended on the percentage of waste used, whereas both analyzed parameters were closely related to the structure of the cement matrix and interfacial transition zone area between the coarse aggregates and the paste. It should be stated that at the content of 20% CFA in the binder composition, an increase in the fcm of the material is observed, with a simultaneous increase in its water absorption. On the other hand, the addition of 30% CFA results in a significant decrease in both the strength of the composite and its water absorption. Thus, it was found that in the case of concretes with the addition of CFA, the strength of the material is directly proportional to the level of its water absorption. Moreover, the concrete including 30% CFA may increase the durability of reinforced concrete structures subjected to immersion conditions. From an application point of view, the obtained research results may be helpful in understanding the impact of the CFA additive on the level of water absorption in cement concretes with this waste.

Development and commercialization of self-healing concrete is hampered due to a lack of standardized test methods. Six inter-laboratory testing programs are being executed by the EU COST action SARCOS, each focusing on test methods for a specific self-healing technique. This paper reports on the comparison of tests for mortar and concrete specimens with polyurethane encapsulated in glass macrocapsules. First, the pre-cracking method was analysed: mortar specimens were cracked in a three-point bending test followed by an active crack width control technique to restrain the crack width up to a predefined value, while the concrete specimens were cracked in a three-point bending setup with a displacement-controlled loading system. Microscopic measurements showed that with the application of the active control technique almost all crack widths were within a narrow predefined range. Conversely, for the concrete specimens the variation on the crack width was higher. After pre-cracking, the self-healing effect was characterized via durability tests: the mortar specimens were tested in a water permeability test and the spread of the healing agent on the crack surfaces was determined, while the concrete specimens were subjected to two capillary water absorption tests, executed with a different type of waterproofing applied on the zone around the crack. The quality of the waterproofing was found to be important, as different results were obtained in each absorption test. For the permeability test, 4 out of 6 labs obtained a comparable flow rate for the reference specimens, yet all 6 labs obtained comparable sealing efficiencies, highlighting the potential for further standardization.

Invisible orthodontic aligners (IOAs) have been introduced in the orthodontic field as an innovative alternative for fixed brackets, in relation to their ability to be easily inserted/removed from the oral cavity without affecting the chewing ability and the aesthetic of the patients. The paper provides a complete physicochemical and mechanical characterization of thermoplastic materials in the form of disks used for commercial IOAs. A wide palette of specific techniques is considered, from tensile tests and dynamic-mechanical analysis, to X-Ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR-ATR) analyses and water absorption tests. The disks are investigated before and after immersion into staining beverages (red wine, coffee, nicotine and artificial saliva), in terms of colour variations, transparency, and microscopic surface modifications by means of colorimetry, UV-VIS absorbance and scanning electron microscopy (SEM). Among all the samples, polyurethane (PU) exhibited the highest crystallinity and the highest values of mechanical and thermal resistance, while the poly(ethylene terephthalate)-glycol (PETG) samples presented better transparency and less ability to absorb water. Moreover, red wine and coffee give noticeable colour variations after 14 days of immersion, together with a slight reduction of transparency.

The present study deals with the fabrication of epoxy composites reinforced with 50 wt% of date palm leaf sheath (G), palm tree trunk (L), fruit bunch stalk (AA), and leaf stalk (A) as filler by the hand lay-up technique. The developed composites were characterized and compared in terms of mechanical, physical and morphological properties. Mechanical tests revealed that the addition of AA improves tensile (20.60–40.12 MPa), impact strength (45.71–99.45 J/m), flexural strength (32.11–110.16 MPa) and density (1.13–1.90 g/cm3). The water absorption and thickness swelling values observed in this study were higher for AA/epoxy composite, revealing its higher cellulosic content, compared to the other composite materials. The examination of fiber pull-out, matrix cracks, and fiber dislocations in the microstructure and fractured surface morphology of the developed materials confirmed the trends for mechanical properties. Overall, from results analysis it can be concluded that reinforcing epoxy matrix with AA filler effectively improves the properties of the developed composite materials. Thus, date palm fruit bunch stalk filler might be considered as a sustainable and green promising reinforcing material similarly to other natural fibers and can be used for diverse commercial, structural, and nonstructural applications requiring high mechanical resistance.

Hydroxypropyl cellulose-g-poly (acrylicacid-co-2-acrylamido-2-methyl-1-propane sulfonic acid)/laterite (HPC-g-P (AA-co-AMPS)/laterite) with excellent water (salt) absorbency, water retention performance, re-swelling property, and fast water absorption rate was prepared by free-radical polymerization. The structure and morphology of the synthetic materials were characterized by FTIR, SEM, and TGA. The water absorbency of superabsorbent resin in different salt solutions was studied, and it was proved that the superabsorbent resin was more sensitive to salt solutions. The swelling kinetic mechanism of superabsorbent resin was explained by pseudo-second-order swelling kinetic model. The effects of the ratio of laterite to loess on water evaporation and the content of superabsorbent resin on soil water evaporation and shrinkage of soil crust were studied.

As a building material, limestone is affected salt and acid solutions resulting from intense weather conditions over time. In the present study, variations in capillary water absorption, porosity, physical changes, and internal rock decomposition mechanisms caused by salt crystallization and air pollutants (SOx and NOx) in sedimentary limestone from the Antalya region were explored. The mineralogical–petrographical and geochemical properties of the limestones were determined using polarizing light microscopy, scanning electron microscopy (SEM), and X-ray fluorescence methods. The variations in the capillary water absorption coefficient, weight, and pore distribution and size were also determined by mercury porosimetry (MIP). An increase in weight was observed in the salt and SA (150 ± 10 mL deionized water and 500 ± 10 mL H2SO3 acid) weathering tests, but a reduction in weight was found under the action of NA (150 ± 10 mL deionized water and 500 ± 10 mL HNO3 acid). The reaction of SA with the limestones influenced the presence of calcium sulphite hemihydrate and gypsum on the rock surface, which affected weight gain. A decrease was observed in the weights of the limestones under the action of NA, and the porous structure seen in the microscale examination from SEM analysis supported a loss of material. The values for capillary water absorption increased in the limestones exposed to salt, SA, and NA. According to MIP analysis, the pore size distribution curves became multimodal, and the pore sizes varied in the studied limestones exposed to salt, SA, and NA. The findings of our study serve as an important guide for the use of limestone as a natural stone in regions with severe weather conditions.

The water-weakening effect is a significant cause of large deformations and damage in rock engineering. In order to accurately describe the stress–strain relationship during the rock damage process, a constitutive model based on statistical distribution has proven to be effective. However, most rock microelements strength is characterized by the Drucker-Prager or Mohr–Coulomb criterion, which fails to account for the influence of the damage threshold on the rock damage metric and presents inconsistencies in the linear stress–strain relationship at low stresses. To address these shortcomings, this study proposes a new statistical damage constitutive model based on the Hoek–Brown criterion that considers the water-weakening effect. The proposed model divides the rock damage process into two stages: water-weakening and stress loading. The rock damage is represented by infinite microelements, with the elastic part following Hooke's law and the damaged part retaining the remaining strength. The strength of the rock microelements follows the Hoek–Brown criterion, and the relationship between rock microelement strength and damage variables is derived using the strain equivalence hypothesis. The proposed model is validated using triaxial test data from representative rock samples subjected to the water-weakening effect and triaxial stress loading under different confining stresses and water absorption rate degrees. Results indicate that the proposed model can accurately express the entire stress–strain curve of rock without exceeding the experimental accuracy, particularly at low confining pressure. Overall, this study demonstrates that the new statistical damage constitutive model has significant potential in accurately describing the stress–strain relationship during the rock damage process, particularly for the presence of the water-weakening effect.

The utilization of a novel monolithic superhydrophobic cement material effectively prevents water infiltration and enhances the longevity of the material. A method for improving superhydrophobic concrete was investigated with the aim of increasing its strength and reducing its cost by compounding superhydrophobic substances with water repellents. The experimental tests encompassed the assessment of the compressive strength, contact angle, and water absorption of the superhydrophobic cementitious materials. The findings demonstrate that an increase in the dosage of isobutyltriethoxysilane (IBTES) progressively enhances the contact angle of the specimen, but significantly diminishes its compressive strength. The contact angle of SIKS mirrors that of SIS3, with a superior compressive strength that is 68% higher. Moreover, superhydrophobicity directly influences the water absorption of cementitious materials, with a more pronounced superhydrophobic effect leading to a lower water absorption rate. The water absorption of cementitious materials is influenced by the combined effect of porosity and superhydrophobicity. Furthermore, FT−IR tests unveil functional mappings, such as -CH3 which can reduce the surface energy of materials, signifying successful modification with hydrophobic substances.

Paving blocks might encounter diverse environmental conditions during their lifespan. The durability of paving blocks is determined by their capacity to endure various exposure conditions. Synthetic fibers have been used in mortar and concrete to improve their properties. This research investigates the influence of including banana fiber (BF) on the physical and mechanical characteristics of mortar. Five different mortar mixes were developed, with varying amounts of BF ranging from 0 to 2% by volume. Testing included ultrasonic pulse velocity, compressive strength, flexural strength, total water absorption, and sorptivity. Specimens were cured for up to 90 days. The results indicate that using 0.5% BF resulted in an improvement in compressive and flexural strength compared to the control mix. There was an increase in total water absorption and the water absorption coefficient in the presence of fibers. There appeared to be good correlations between the compressive strength and the other properties examined.