Search Results (539)

Gas nitriding was implemented in the current work at a constant nitrogen potential (K_N) of 2.0 for 8 h to enhance the fatigue properties of SCM 440 steel, and the results were compared with those of the substrate tempered at the nitriding temperature (475 °C). Fine particle peening (FPP) prior to nitriding imposed a refined structure and induced compressive residual stress (CRS) in the near-surface peened zone. The fine-grained structure provided numerous paths to enhance nitrogen diffusion inwards during nitriding. The compound layer formed on the nitrided SCM 440 steel primarily comprised a mixture of Fe₃N and Fe₄N; however, the pre-peened and nitrided (SPN) specimens exhibited a higher proportion of Fe₃N and a thicker compound layer than the non-peened and nitrided (NPN) counterparts. In addition, FPP prior to nitriding increased both the case depth and the magnitude of the CRS field compared with nitriding alone. The fatigue limits of the substrate (SB), NPN, and SPN samples were approximately 750, 1050, and 1400 MPa, respectively. Gas-nitriding at 475 °C significantly improved the fatigue performance of SCM 440 steel. Moreover, pre-peening prior to nitriding further enhanced fatigue strength and life of the treated SCM 440 steel by introducing a deeper case depth and higher CRS field. Multiple cracks initiation at the outer surface of the SB sample accounted for its lowest fatigue limit among the tested samples. Surface microcracks and pits on the surface of the NPN specimen would be crack initiation sites and harmful to its fatigue resistance. These surface dents were considered to be responsible for fatigue crack initiation in the SPN specimens. Therefore, polishing after nitriding to reduce surface roughness and/or microcracks was expected to further increase the fatigue resistance and the reliability of nitrided SCM 440 steel. Full article

Polymer-based product usage in modern society is increasing day by day. Following usage, these inert products and hydrophobic materials contribute to environmental pollution, often accumulating as litter in ecosystems and contaminating water bodies. The rapid socio-economic development in the Kingdom of Saudi Arabia (KSA) has resulted in a significant increase in waste generation. This study was conducted on the utilization of recycled plastic waste (RPW) polymer along with commercial polymer (CP) for the modification of the local binder. The hot environmental conditions and increased traffic loading are the major reasons for the permanent deformation and thermal cracks on the pavements, which require improved and modified road performance materials. The Ministry of Transport and Logistical Support (MOTLS) in Saudi Arabia, along with other related agencies, spends a substantial amount of money each year on importing modifiers, including chemicals, hydrocarbons, and polymers, for modification purposes. This research was conducted to investigate and utilize available local recycled plastic materials. Comprehensive laboratory experiments were designed and carried out to enhance recycled plastic waste, including low-density polyethylene (rLDPE), high-density polyethylene (rHDPE), and polypropylene (rPP), combined with varying percentages of commercially available polymers such as Styrene-Butadiene-Styrene (SBS) and Polybilt (PB). The results indicated that incorporating recycled plastic waste expanded the binder’s susceptible temperature range from 64 °C to 70 °C, 76 °C, and 82 °C. The resistance to rutting was shown to have significantly improved by the dynamic shear rheometer (DSR) examination. Achieving the objectives of this research, combined with the intangible environmental benefits of utilizing plastic waste, provides a sustainable pavement development option that is also environmentally beneficial. Full article

To overcome the limitations of conventional high-viscosity high-elasticity modified asphalt, including high production costs, phase separation, and thermal degradation, this study introduces a novel fast melting Styrene-Butadiene-Styrene modifier (SBS-T) for asphalt modification. The primary novelty of SBS-T lies in its ability to mitigate phase separation and thermal degradation while simplifying the production process, thereby offering a more robust and cost-effective alternative. The viscoelastic properties of SBS-T-modified asphalt were characterized through frequency sweep tests under varying loading conditions, while its fatigue behavior was quantitatively assessed using the Simplified Viscoelastic Continuum Damage (S-VECD) model. The results indicate that the SBS-T-modified asphalt exhibits outstanding viscoelastic performance across a broad range of temperatures and loading frequencies, and can better adapt to the temperature and load changes in complex pavement environments. Among them, the influence of long-term aging on the linear viscoelastic characteristics of SBS-T-modified asphalt is greater than that of ultraviolet aging. The SBS-T-modified asphalt also shows better stiffness and resistance to shear deformation. The fatigue life of asphalt gradually decreases with the deepening of the aging degree, among which the impact of long-term aging on fatigue life is greater than that of ultraviolet aging. Under different aging conditions, SBS-T-modified asphalt has shown good fatigue performance and is suitable for practical engineering applications. Full article

This study investigates the fabrication and performance of a novel composite material by infiltrating SnSb11Cu6 babbitt alloy into an open-cell AlSn6Cu-SiC matrix. The composites, produced via a multi-stage liquid-state processing route, were comprehensively characterized for their microstructural, mechanical, and tribological properties. The inclusion of 5 wt.% silicon carbide reinforcement resulted in a significant improvement in tribological performance under dry-sliding conditions. Specifically, the reinforced composite exhibited a 24.8% reduction in wear and a 10.8% reduction in the coefficient of friction compared to its unreinforced counterpart. Crucially, this enhancement in wear resistance was achieved while the bulk compressive mechanical properties and ductile deformation behavior remained virtually identical to the unreinforced material. Microstructural analysis confirmed that the high-hardness SiC particles act as primary load-bearing agents, shielding the softer metallic matrix from severe wear. These findings demonstrate the successful development of a high-performance composite with enhanced tribological durability without a mechanical trade-off, making it a promising candidate for advanced bearing applications. Full article

Moisture damage remains a primary distress mechanism in asphalt pavements, leading to reduced service life and viscoelastic property loss due to weakened asphalt–aggregate adhesion. This study evaluated moisture susceptibility in eight asphalt mixtures combining two aggregates (limestone/granite) and four binders (two neat, two SBS-modified) using dynamic mechanical analysis (DMA). Thin-section specimens underwent DMA temperature sweeps under dry and water-immersed conditions to characterize shifts in viscoelastic properties. Results demonstrated that moisture exposure significantly reduced complex modulus values and shifted characteristic temperatures (T₀, T₁, T₂, T_g) toward lower ranges, indicating compromised performance. Specifically, granite mixtures showed average reductions in T₀, T₁, and T_g of 2.9 °C, 1.8 °C, and 3.7 °C, respectively, compared to 2.1 °C, 1.5 °C, and 1.7 °C for limestone mixtures. The magnitude of these changes—quantified by residual modulus (RM) ratios and characteristic temperature differentials—effectively ranked mixture susceptibility, with granite mixtures and specific binders (A1, B1) showing higher sensitivity. Notably, minimum residual modulus (RM_min) values ranged from 28.2% to 65.8%, and its critical temperature (T_RM) identified the most severe moisture damage conditions (approximately 40 °C for neat asphalt; 60 °C for modified asphalt). The DMA-derived indices correlated with surface free energy-based adhesion work, confirming the method’s reliability for rapid moisture sensitivity assessment. This approach provides an efficient basis for selecting moisture-resistant materials tailored to operational temperature environments. Full article

Microorganisms present in asphalt pavement service environments can alter the composition of asphalt through metabolic activities, thereby affecting its rheological properties. To investigate this influence and compare performance variations across asphalt types, two asphalt-degrading bacterial strains were isolated from in-service pavements. Following 16S rRNA gene sequencing and phylogenetic analysis, the strains were identified as Pseudomonas putida and a putative novel species within the Citrobacter genus. Using a custom-designed thin-film inoculation system, the performance evolution of base asphalt and styrene-butadiene-styrene (SBS) modified asphalt was systematically evaluated after microbial activity periods of 5, 10, and 15 days. Conventional property tests and multi-temperature rheological analyses (temperature sweep, multiple stress creep recovery test, linear amplitude sweep, 4 mm DSR) were conducted. Results demonstrated that microbial action reduced penetration, elevated softening point, and decreased ductility in both asphalt types, with more pronounced changes observed in base asphalt. High-temperature rheological parameters (G*/sinδ), recovery rate, and non-recoverable creep compliance indicated compromised resistance to permanent deformation. SBS-modified asphalt substantially mitigated these detrimental effects. Fatigue life of base asphalt decreased overall with periodic fluctuations, whereas SBS-modified asphalt exhibited superior fatigue stability: after an initial decline at 5 days, performance recovered and stabilized between 10 and 15 days. Low-temperature performance showed slight improvement in base asphalt, while SBS-modified asphalt demonstrated significant enhancement during later activity stages. Full article

Growing environmental concerns and the depletion of fossil-based resources have accelerated the demand for sustainable alternatives in engineering and construction materials. Among these, bio-based composites have gained attention for their use of renewable and eco-friendly resources. Macadamia nutshells, typically treated as agricultural waste, possess high strength, brittleness, heat resistance, and fracture toughness, making them attractive candidates for structural applications. Australia alone contributes nearly 40% of global macadamia production, generating significant shell by-products that could be repurposed into high-value composites. This study investigates the development of novel composite cores and sandwich structures using macadamia nutshell particles reinforced in an epoxy polymer matrix. Two weight ratios (10% and 15%) and two particle sizes (200–600 µm and 1–1.18 mm) were employed, combined with laminating epoxy resin and hardener to fabricate composite cores. These cores were further processed into sandwich specimens with carbon fabric skins. Flexural and short beam shear (SBS) tests were conducted to evaluate the mechanical behaviour of the composites. The results demonstrate that higher filler content with fine particles achieved up to 15% higher flexural strength and 18% higher stiffness compared to coarser particle composites. Sandwich structures exhibited markedly improved interlaminar shear strength (8–15 MPa), confirming superior load transfer and durability. The results demonstrate that higher filler content and finer particles provided the most favourable mechanical performance, showing higher flexural strength, stiffness, and shear resistance compared to coarser particle formulations. Sandwich structures significantly outperformed core-only composites due to improved load transfer and resistance to bending and shear stresses, with the 15% fine-particle configuration emerging as the optimal formulation. By transforming macadamia nutshells into value-added composites, this research highlights an innovative pathway for waste utilisation, reduced environmental impact, and sustainable material development. The findings suggest that such composites hold strong potential for structural applications in construction and related engineering fields, especially in regions with abundant macadamia production. This study reinforces the role of agricultural by-products as practical solutions for advancing green composites and contributing to circular economy principles. Full article

The mastic asphalt mixture (MA) is one of the first mineral and asphalt mixtures used in history. Its composition and structure allow it (the mixture) to be produced both in industrial conditions (in mineral and asphalt mixing plants) and in field conditions—in mobile boilers (especially when the produced mixture is used to repair damaged surface). The high proportion of the sand fraction makes the mixture highly workable, allowing it to be laid/incorporated without special equipment. MA, however, also has some drawbacks. The asphalt content is higher than in other mixtures, which can make it prone to plastic deformation. Mastic asphalt requires higher processing temperatures than other “hot” mixtures. Mastic asphalt mixtures are installed as road pavement layers and, because of their high density, as the protective layer on roof felt isolation on bridge decks. The high temperature of embedding creates a risk of damaging the roof felt, as its typical temperature resistance is lower than 180 °C, whereas the temperature of the mastic asphalt mixture is higher. The use of zeolites can enable reconciliation of technological requirements of mastic asphalt and asphalt roof isolation. The mixes MA 8 and MA 11 containing 0 and 5% of two types of zeolites and asphalt binders 35/50 or elastomer-SBS-modified asphalt binder PMB 25/55-60 were used in the research. Laboratory tests revealed that the addition of a 5% amount of zeolite by asphalt mass makes it possible to reduce the mastic asphalt laying temperature by up to 30 °C, which seems to be very important from ecological, economical, and pavement durability points of view. Full article

The durability of asphalt pavements is crucial for sustainable road infrastructures. This systematic review compares the Marshall and Superpave asphalt mix design protocols, with a particular focus on the integration of polymer-modified bitumen (PMB) and rejuvenators. Although the Marshall method remains widely used for its simplicity and cost-efficiency, its empirical basis limits its effectiveness to meet modern pavement performance demands. In contrast, the Superpave system offers improved resistance to rutting, longer fatigue life, and better mitigation of moisture damage. The review traces the evolution of asphalt mix design, identifies current challenges, and emphasizes the need for transitioning toward performance-based frameworks. Special attention is given to the incorporation of polymers such as Styrene–Butadiene–Styrene (SBS), Styrene–Butadiene–Rubber (SBR), and Polyethylene (PE), which significantly enhance the mechanical properties of asphalt mixtures. The role of rejuvenators in restoring aged binders and enabling pavement recycling is also examined. Finally, the manuscript provides strategic recommendations for adopting Superpave to enhance pavement durability and reduce lifecycle maintenance costs. Overall, this comprehensive review advances knowledge on asphalt mix design, fostering innovation and sustainability while promoting long-term resilience in road pavement infrastructures. Full article

Latent stripping has become increasingly apparent in asphalt pavements, particularly in highway rehabilitation and international construction projects supported by Official Development Assistance (ODA) from the Government of Japan. Stripping accelerates structural deterioration, making countermeasures essential. However, in ODA projects, securing high-quality aggregates or evaluating local materials is often difficult due to environmental and budgetary constraints. This study focused on Surface Free Energy (SFE) as a small-sample evaluation method and developed ten types of styrene–butadiene–styrene (SBS) polymers to enhance interfacial adhesion by targeting aggregate surface functional groups. The SFE of each Polymer-Modified Bitumen (PMB) and thirteen aggregates was measured, and the work of adhesion and moisture sensitivity index (MSI) were calculated for all combinations. Twenty-one Hot-Mix Asphalts (HMA) were then prepared and evaluated using the Hamburg Wheel Tracking Test (HWTT) based on load cycles to stripping initiation (LC_SN) and to 12.5 mm rut depth (LC_ST). The developed PMBs showed a higher work of adhesion, a lower MSI, and substantially increased LC_SN and LC_ST values. Strong negative correlations were observed between MSI and both HWTT indicators, confirming the utility of SFE-based MSI for material screening. This study demonstrates that interface-targeted PMBs can improve stripping resistance, thereby promoting the use of lower-quality aggregates in durable pavements. Full article

This work reports a low-cost, microwave-assisted wet chemistry synthesis of zinc antimonate (ZnSb₂O₆) powders with a trirutile structure, yielding highly homogeneous, nanometric particles. X-ray diffraction (XRD) confirmed the formation of the trirutile phase with lattice parameters of a = 4.664 Å and c = 9.263 Å, and an estimated crystallite size of 42 nm. UV–vis spectroscopy revealed a bandgap of 3.35 eV. Scanning electron microscopy (SEM) showed that ethylenediamine, as a chelating agent, formed porous microstructures of microrods and cuboids, ideal for enhanced gas adsorption. Brunauer–Emmett–Teller (BET) analysis revealed a specific surface area of 6 m²/g and a total pore volume of 0.0831 cm³/g, indicating a predominantly mesoporous structure. The gas sensing properties of ZnSb₂O₆ pellets were evaluated in CO and C₃H₈ atmospheres at 100, 200, and 300 °C. The material exhibited high sensitivity at 300 °C, where the maximum responses were 5.86 for CO at 300 ppm and 1.04 for C₃H₈ at 500 ppm. The enhanced sensitivity at elevated temperatures was corroborated by a corresponding decrease in electrical resistivity. Furthermore, the material demonstrated effective photocatalytic activity, achieving up to 60% degradation of methylene blue and 50% of malachite green after 300 min of UV irradiation, with the process following first-order reaction kinetics. These results highlight that ZnSb₂O₆ synthesized by this method is a promising bifunctional material for gas sensing and photocatalytic applications. Full article

Today, several conventional wastes (fly ash, ground granulated blast furnace slags, etc.) are used as valid precursors for geopolymer synthesis. However, there are several new wastes that can be studied to replace geopolymer precursors. This study investigates the behavior of four industrial wastes—suction dust (SW1), red mud (SW2), electro-filter dust (SW3), and extraction sludge (SW4)—as 20 wt.% substitutes for metakaolin in geopolymer synthesis. The objective is to assess how their incorporation before alkali activation affects the structural, thermal, mechanical, chemical, and antimicrobial properties of the resulting geopolymers, namely GPSW1–4. FT-IR analysis confirmed successful geopolymerization in all samples (the main Si-O-T band underwent redshift, confirming Al incorporation in geopolymer structures after alkaline activation), and stability tests revealed that none of the GPSW1–4 samples disintegrated under thermal or water stress. However, GPSW3 showed an increase in efflorescence phenomena after these tests. Moreover, compressive strength was reduced across all waste-containing geopolymers (from 22.0 MPa for GP to 12.6 MPa for GPSW4 and values lower than 8.1 MPa for GPSW1–3), while leaching tests showed that GPSW1 and GPSW4 released antimony (127.5 and 0.128 ppm, respectively) above the legal limits for landfill disposal (0.07 ppm). Thermal analysis indicated that waste composition influenced dehydration and decomposition behavior. The antimicrobial activity of waste-based geopolymers was observed against E. coli, while E. faecalis showed stronger resistance. Overall, considering leaching properties, SW2 and SW3 were properly entrapped in the GP structure, but showed lower mechanical properties. However, their antimicrobial activity could be useful for surface coating applications. Regarding GPSW1 and GPSW4, the former needs some treatment before incorporation, since Sb is not stable, while the latter, showing a good compressive strength, higher thermal stability, and leaching Sb value not far from the legal limit, could be used for the inner reinforcement of building materials. Full article

This study presents the electrical and optical properties of 35P₂O₅–xV₂O₅–(65–x) Sb₂O₃ glasses for 0 ≤ x ≤ 65 mol%. The direct current (DC) resistivity was measured by the Van der Pauw method and optical absorption spectra were taken in the Ultraviolet–Visible-Near-Infrared (UV–VIS–NIR) range. Electrical transport is attributed to simultaneous hopping of small polarons (SPs) between V⁴⁺ and V⁵⁺ (vanadium ion) sites and small bipolarons (SBPs) between the Sb³⁺ and Sb⁵⁺ (antimony ion) sites. The resistivity exhibits a non-linear dependence on the ionic fraction of vanadium (n_v), whereas the resistivity exhibits a minimum in the composition range 0 ≤ n_V ≤ 0.3, and a resistivity maximum was observed in the range 0.3 ≤ n_V ≤ 0.5. On further increasing n_v, the resistivity exhibits a monotonic decline. In the composition range 0 ≤ n_V ≤ 0.3, where the hopping distance between V ions decreases, while that between the Sb ions increases, the resistivity minimum has been shown to be the consequence of decreasing tunneling distance of SPs between the V⁴⁺ and V⁵⁺ ion sites. In the composition range 0.3 ≤ n_V ≤ 0.5, the resistivity, activation energy for DC conduction, glass transition temperature, and density exhibit their respective maxima even though the separation between the V⁴⁺ and V⁵⁺ sites continues to decrease. This feature is explained by enhanced localization of electrons on account of increased disorder (entropy) among the SPs and SBPs, like that of Anderson localization. This argument is further supported by a shift in the polaronic optical absorption bands associated with the SPs and SBPs toward higher energies. The transport behavior of all the glasses except the x = 0 composition has been explained by adiabatic transport, principally, by the SPs on V ions while the Sb ions contribute little to the total transport process. The results provide a clear relation between composition, polaron/bipolaron contributions, and conduction in these glasses. Full article

The NRAMP (Natural Resistance-Associated Macrophage Protein) family plays a pivotal role as membrane transporters in plants’ responses to heavy metal stress. This study identified 12 NRAMP genes in Sorghum bicolor (sorghum) and performed a comprehensive bioinformatics analysis. The SbNRAMP genes are distributed across seven sorghum chromosomes. In-depth analyses of gene structure, conserved motifs, collinearity, and phylogeny indicated that the SbNRAMP family is divided into three subfamilies, each exhibiting unique structural and motif characteristics. Collinearity analysis suggested that large-fragment duplications, rather than tandem duplications, were responsible for the expansion of the SbNRAMP family, resulting in a greater number of genes compared to Arabidopsis thaliana and rice. Transcriptome analysis of the aboveground and underground parts of sorghum seedlings under saline–alkali stress revealed that SbNRAMP5 is a key hub gene exhibiting tissue-specific expression. Furthermore, qRT-PCR analysis following exposure to Cd, Mn, or Zn treatments revealed differential expression among the SbNRAMP genes. Subcellular localization predictions indicated that all twelve NRAMPs are primarily located in the plasma membrane, with nine to twelve transmembrane domains, consistent with their function in metal ion transport. Experimental evidence confirmed that SbNRAMP6 is localized in the plasma membrane. These findings establish a foundation for a deeper understanding of the structure and function of the sorghum NRAMP gene family. Full article

This study examined the synergistic effects of Styrene–Butadiene–Styrene (SBS) polymer and nanoclay on asphalt concrete mixture performance through a systematic experimental program using 4.5% SBS with varying nanoclay concentrations (0–8%). Performance evaluation included Indirect Tensile Strength (ITS), Indirect Tensile Resilient Modulus (E_RI), and Hamburg Wheel Tracking Tests (HWTT), along with novel quantitative analysis of visco-plastic and moisture resistance indices. Results demonstrated that 4.5% SBS with 6% nanoclay (4.5S6N) yielded optimal performance, achieving 38% increase in dry ITS, 68% improvement in wet ITS, and enhanced moisture resistance with Tensile strength Ratio (TSR) improving from 79.53% to 97.14%. The E_RI value increased by 39%, while rutting resistance improved by 39.3%. At this optimal concentration, nanoclay’s uniform dispersion and layered silicate structure created an effective reinforcement network, enhancing stress distribution and interfacial bonding with the SBS polymer network and asphalt components. However, exceeding 6% nanoclay content led to performance deterioration due to particle agglomeration. These findings demonstrate that optimized SBS–nanoclay modification effectively addresses both mechanical and moisture-related performance requirements for modern pavement applications. Full article