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This PRISMA-guided scoping review examines the use of waste materials in civil engineering as a sustainable approach to reducing environmental impacts, conserving natural resources, and supporting circular economy principles. The rapid growth of urbanization, industrialization, mining, and agricultural activities generates large amounts of waste materials, including fly ash, ground granulated blast-furnace slag, bauxite residue, mining tailings, waste rock, acid-mine drainage sludge, waste plastics, post-consumer vulcanized rubber, recycled construction materials, and agricultural ashes. The disposal of these materials often creates serious environmental and land-use problems, making their reuse increasingly important. In this context, civil engineering is one of the most promising sectors for large-scale waste valorization because of its high material demand and its ability to use different waste streams into practical applications such as concrete and cementitious systems, pavement and asphalt engineering, geotechnical works, and other infrastructure sectors. This review critically evaluates the global availability, material characteristics, engineering applications, environmental and economic benefits, recent advances, and key challenges related to major industrial, mining, agricultural, polymeric, and construction-derived wastes. Although significant progress has been made in this field, wider implementation is still limited by variations in material properties, technical and environmental challenges, economic constraints, and limited field validation of long-term performance. By bringing together current knowledge from different waste streams and civil engineering sectors, this review highlights important research gaps and future directions to support more sustainable, resilient, and resource-efficient infrastructure development. The effective use of waste materials in civil engineering can play an important role in reducing carbon emissions, improving resource efficiency, and supporting global sustainability.
The empirical Delany-Bazley model and several of its subsequent modifications were evaluated to determine their ability to predict the sound absorption coefficient spectra of porous materials. The study considered three porous materials (foam, mineral wool and samples made from recycled cigarette butt) with different thicknesses. Model performance was assessed by comparing theoretical predictions with impedance tube measurements using the root mean square error (RMSE). Although some models yielded lower prediction errors for specific materials and thicknesses, the results showed that sample thickness-and the associated changes in the shape of the sound absorption spectrum-have a greater influence on model performance than the material itself. No single empirical model consistently provided the best agreement over the entire thickness range. These findings suggest that the applicability of Delany-Bazley-type empirical models appears to be more closely related to the shape of the sound absorption spectrum than to the material for which they were originally developed. These findings provide practical guidance for selecting suitable models for both conventional and recycled porous sound absorbers.
Terahertz (THz) radiation generated through ultrafast transient photocurrent mechanisms has become a cornerstone of modern THz photonics, enabling broadband coherent emission with sub-picosecond temporal resolution. This review provides a comprehensive and mechanism-driven analysis of THz pulse generation via photo-Dember diffusion currents, surface depletion field acceleration, and biased photoconductive antenna architectures. We present a comprehensive comparative analysis of wide- and low-bandgap material platforms, including III-V, II-VI, and group IV semiconductors, as well as two-dimensional materials, topological insulators, and Weyl semimetals, highlighting how their intrinsic properties, such as band structure, carrier mobility, recombination dynamics, doping, and dielectric response, govern their THz emission efficiency, bandwidth, and spectral tunability. Special emphasis is placed on germanium (Ge), which has re-emerged as a highly promising THz source material owing to its high carrier mobility, long diffusion lengths, strain-tunable band structure, and CMOS compatibility. We highlight the roles of doping, strain-induced direct transitions, and several fabrication techniques in controlling the nonlinear photoexcited charge-carrier dynamics in Ge, thereby unlocking enhanced broadband THz performance. Finally, we explore the emerging application prospects of THz radiation, ranging from non-invasive security screening to biochemical sensing and archeological preservation. By bridging fundamental material science with scalable device architectures, this review outlines current challenges, highlights evolving opportunities in novel materials, and charts future directions towards integrated THz technologies.
This study presents a numerical investigation of the dynamic response of a typical low-rise building subjected to recorded mine-induced vibrations, with particular emphasis on the role of construction material type. Several structural variants consistent with the real building configuration were analysed using a validated three-dimensional finite element (3D FEM) model. Seven load-bearing wall materials were considered, including reinforced concrete, lightweight concrete, cellular concrete, standard brick, and selected sand-lime bricks. Dynamic responses were evaluated in terms of displacements and accelerations, including time histories along the building axis, peak component values, resultant responses, and Fourier spectra. The results clearly demonstrate that material properties-especially stiffness-govern the dynamic behaviour of the structure. Low-stiffness materials, such as cellular concrete, significantly amplify both acceleration and displacement responses, increasing susceptibility to vibration-induced effects. Moreover, the dominant vibration frequencies were found to vary depending on the wall material, which directly affects resonance conditions and potential damage risk. A notable sensitivity of the calculated response to the choice of numerical evaluation point within the structure was also observed. The findings highlight the critical importance of material selection in controlling the dynamic performance of low-rise buildings exposed to mining-induced vibrations and provide practical guidance for mitigating paraseismic effects in engineering design.
The CaO-Al2O3-Fe2O3 system is widely encountered in cement production, iron ore sintering, metallurgical slags, and refractory materials. A thermodynamic assessment of the CaO-Fe2O3 and CaO-Al2O3-Fe2O3 systems was carried out in this study based on the CALculation of PHAse Diagrams (CALPHAD) method. The liquid was modeled using the ionic two-sublattice model, expressed as (Ca+2, Al+3, Fe+2) P (O-2, AlO1.5, FeO1.5, Va, O) Q. The Compound Energy Formalism (CEF) was adopted to describe compounds and solid solutions. A self-consistent thermodynamic assessment of the CaO-Fe2O3 and CaO-Al2O3-Fe2O3 systems was achieved, enabling accurate reproduction of phase equilibrium and thermodynamic data. The obtained thermodynamic description provides a useful foundation for the design, optimization, and processing of refractory materials.
This study investigates the environmental potential and viability of replacing natural river aggregates (RAs) with copper slag aggregates (CSAs) in concrete production. The primary objective was to assess the structural performance of these eco-concrete mixtures and determine the optimum copper slag content for structural applications. The experimental program evaluated concrete mixtures with natural river aggregate replacement levels of 20% + 20% and 50% + 100% for the 8/16 mm and 16/32 mm fractions, respectively, using coarse copper slag aggregate (CCA). The results indicate that incorporating CCA increases concrete compressive strength, successfully meeting the requirements for strength class C25/30. The petrographic assessment indicated a shift towards an aggregate mixture, in which the dominant quartzite and a constant quartz-mineral fraction of 16.5% provide a stable structure alongside the CSA grains. However, a significant increase in water penetration depth (up to 22%) was observed, highlighting the enhanced water penetration depth of these concretes. SEM microstructural analysis attributed the improved bond between the cement matrix and CCA grains to a compact interfacial transition zone. Additionally, leaching tests confirmed that heavy metals are effectively immobilized in the cement paste for mixtures with lower replacement levels (up to 20%), thereby meeting environmental standards. The study concludes that copper slag at these controlled replacement levels represents a sustainable, high-quality alternative for construction materials in drainage infrastructure. Incremental analysis in accordance with NEN 7375 showed that the tested material behaves as an insoluble matrix, with no evidence of diffusion-controlled leaching. The cumulative leaching values obtained after 64 days of testing in accordance with NEN 7375 were significantly below the regulatory limits for all components analyzed. These findings indicate a low potential for contaminant release and favorable environmental stability of the 20% replacement mixture, though further leaching evaluation is required for maximum slag contents.
Cementitious sand and gravel (CSG) is commonly used in construction engineering; however, its mix proportion design is complex, and traditional physical experiments face limitations such as long cycles, high costs, and susceptibility to external factors when obtaining high-quality sample data. In this study, a foundational dataset was first acquired through physical experiments: 100 sets of CSG specimens with different mix proportions (cement content 40, 50, 60, 70 kg/m3; water-to-binder ratio 1.0, 1.2, 1.4; sand ratio 0.1, 0.2, 0.3, 0.4; fly ash content 20, 30, 40, 50 kg/m3) were prepared. After 28 days of standard curing, compressive strength and splitting tensile strength tests were conducted using a WAW-1000 electro-hydraulic servo universal testing machine, yielding 100 sets of real mechanical property data. The coefficients of variation for all test groups were below 10%, confirming the reliability and repeatability of the experimental data. On this basis, a data augmentation method based on Conditional Tabular Generative Adversarial Networks (CTGAN) is proposed. Through adversarial training between the generator and the discriminator, the model learns the multi-dimensional distribution characteristics of the original CSG data and generates 100 synthetic samples, which are then merged with the original data to expand the dataset to 200 samples. The quality of the synthetic data is evaluated using Wasserstein distance and correlation matrix heatmaps. Furthermore, a hybrid XGBoost-LSTM prediction model is proposed-XGBoost is used for feature construction to capture nonlinear interactions among mix proportion variables, and the constructed features are then fed into an LSTM network for sequential learning and regression prediction. The results show that the CTGAN-generated data are highly consistent with the original data in terms of kernel density distributions and variable correlations, with Wasserstein distance significantly superior to four comparative methods: Bootstrap, SMOTE, GaussianCopula, and TVAE. After augmentation, the XGBoost-LSTM model achieves a coefficient of determination (R2) of 0.9897 for compressive strength prediction (vs. 0.9793 before augmentation) and 0.9801 for splitting tensile strength (vs. 0.9882 before augmentation, a slight decrease). The mean absolute percentage errors (MAPE) are 4.49% and 4.11%, and the root mean square errors (RMSE) are 0.201 and 0.049, respectively; both error metrics are reduced compared with those before augmentation. Compared with baseline models including XGBoost, LSTM, Random Forest (RF), and Support Vector Regression (SVR), the XGBoost-LSTM model exhibits the best performance across all evaluation metrics, and Wilcoxon signed-rank tests confirm that the performance differences are statistically significant (p < 0.05). The proposed method of CTGAN-based data augmentation combined with the XGBoost-LSTM hybrid model provides an effective solution to the problem of insufficient CSG sample data and offers a reference for data enhancement and performance prediction of other small-sample materials.
Ultralow-reflection electromagnetic interference (EMI) shielding across broad frequency ranges remains elusive as low reflection and low transmission are rarely achieved simultaneously, particularly in lightweight aerogels amenable to scalable manufacturing. Here, a continuous-conductivity-gradient (CCG) aerogel with machine-learning (ML)-assisted optimization is developed via diffusion-controlled in situ oxidative polymerization of pyrrole within an as-prepared, mechanically resilient porous aramid nanofiber scaffold, followed by an energy-efficient, scalable ambient-pressure-drying strategy. The resulting CCG aerogel integrates a continuous through-thickness gradient of polypyrrole (PPy) with a highly porous architecture, enabling a smooth impedance transition and progressive bulk microwave attenuation for ultrabroadband, ultralow-reflection EMI shielding. The optimized CCG aerogel delivers an effective absorption-dominated frequency bandwidth of 29.76 GHz spanning 10.24-40 GHz, with an EMW reflectivity below 0.1, while maintaining an EMI shielding effectiveness above 40 dB across the ultrabroadband frequency range of 8.2-40 GHz, surpassing the shielding performance of existing EMI shielding materials. Mechanistic analyses reveal that the continuous gradient couples efficient front-surface impedance matching with progressive internal dissipation, thereby circumventing the impedance discontinuities inherent to discrete multilayers. Overall, this ML-assisted strategy integrates novel electromagnetic and structural design with robust, scalable all-organic aerogel manufacturing, offering a general platform for ultrabroadband, ultrahigh-absorption, ultralow-reflection EMI shielding across diverse material systems.
Nickel-based alloys are promising structural materials for molten salt systems; however, secondary-phase formation during long-term high-temperature exposure may introduce local corrosion susceptibility because secondary phases have compositions and redox stabilities distinct from the matrix. Here, we combine CALculation of PHAse Diagrams (CALPHAD)-based phase prediction with redox thermodynamic analysis to assess phase-specific corrosion susceptibility in Inconel 625 (IN625) and SA508 low-alloy steel under molten chloride conditions. Equilibrium phase constitutions at 1000 K were predicted using Thermo-Calc, and redox equilibrium potentials were calculated for representative-phase dissolution reactions of major metallic elements in each phase. The dominant α and γ phases in SA508 exhibited similar Fe-ionization potentials of -1.728 and -1.768 V vs. Cl2/Cl-, respectively. In IN625, the γ matrix exhibited a Cr-ionization potential of -1.964 V vs. Cl2/Cl-, whereas the P phase showed the most negative potential of -2.132 V vs. Cl2/Cl-, 0.168 V more negative than the matrix, identifying the P phase as the primary local thermodynamic weak point. These results show that phase-specific metal-ionization susceptibility cannot be inferred solely from nominal alloy composition or matrix behavior. The proposed framework provides a thermodynamic screening approach for identifying susceptible secondary phases in multicomponent alloys under molten-salt conditions.
To address the challenge of simultaneously achieving broadband absorption, multi-mechanism tunability, and angular stability in terahertz multifunctional devices, this paper proposes a MoS2/VO2 composite terahertz metamaterial absorber based on an asymmetric multi-nested C-shaped structure. The device adopts a three-layer configuration consisting of a MoS2/VO2 composite plane-SiO2 dielectric-Au reflector layer. Unlike conventional symmetric structures, which are limited by selection rules and symmetry-protected dark modes that hinder the excitation of higher-order resonances, this design effectively breaks structural symmetry protection through geometric asymmetry. This induces strong mode hybridization between originally orthogonal dark and bright modes, enabling broadband high absorption exceeding 96.7% across the 1.88-3.52 THz frequency range (61% RBW). Notably, the device demonstrates synergistic tuning advantages: the macroscopic on/off switching of broadband absorption characteristics via the phase transition of VO2, combined with fine blind-spot compensation and enhancement in absorption peaks using the electrical tunability of MoS2. Furthermore, thanks to its sub-wavelength unit cell design, the structure maintains excellent performance stability over a wide incident angle range from 0° to 60°. This study reveals a synergistic enhancement mechanism combining the asymmetric unit cell and hybrid materials, providing a systematic physical solution for resolving the trade-off between bandwidth extension and dynamic reconfigurability.
When metal oxides are employed as anodes in lithium-ion batteries, their practical application is often constrained by sluggish reaction kinetics. Structure optimization and heterointerface regulation are effective strategies for improving the aforementioned issue. Herein, a series of Co3O4/ZnCo2O4 heterostructured materials with hollow structures is prepared. The effects of the two-phase ratio on the interfacial activity and electrochemical performance are systematically investigated. Among them, the optimized Co3O4/ZnCo2O4-2 material exhibits enhanced interfacial interactions and abundant oxygen vacancies, which optimize the local electronic environment and facilitate charge transfer. Electrochemical test results indicate that the Co3O4/ZnCo2O4-2 anode maintains a reversible capacity of 582.4 mAh g-1 after 1000 cycles at 1 A g-1, demonstrating good cycling stability. Furthermore, the full cell assembled with a LiFePO4 cathode maintains a discharge capacity of 115.9 mAh g-1 after 100 cycles at 0.2 C, validating the practical application potential of the material. This work reveals the key role of interface regulation in boosting Li+ diffusion kinetics of transition metal oxides, providing new insights for the rational design of heterostructured anodes.
Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer electrolytes suffer from low ionic strength and poor mechanical performance. Meanwhile, lithium lanthanum titanate (LLTO) fillers exhibit severe agglomeration and weak interfacial compatibility with the polymer matrix. To solve these problems, 3-glycidoxypropyltrimethoxysilane (KH560) at four different concentrations (1 wt%, 2 wt%, 3 wt%, 4 wt%) was loaded onto polydopamine-modified LLTO (PDA@LLTO). The modified materials were mixed with PVDF-HFP, and composite solid electrolytes were fabricated by the solution casting method. The epoxy groups in KH560 undergo ring-opening reactions with amino and hydroxyl moieties on PDA, while its trimethoxysilane groups crosslink with the polymer matrix, forming a robust "LLTO-PDA-KH560-polymer" interfacial structure. This dual modification markedly improves the dispersion of PDA@LLTO, strengthens interfacial adhesion, and enhances the mechanical and electrochemical properties of the composite electrolyte. All KH560 loadings suppress LLTO agglomeration, and the 3 wt% grafting ratio yields the optimal performance: a uniform and dense microstructure, a room-temperature ionic conductivity of 5.92 × 10-4 S cm-1, an electrochemical stability window extended to 4.88 V, and a tensile strength over 50% higher than the ungrafted sample. The modified electrolyte effectively inhibits lithium dendrite growth and enhances the cycling stability of solid-state batteries. This work demonstrates that KH560-PDA synergistic modification enables comprehensive performance optimization of composite electrolytes, offering a viable strategy for designing high-performance electrolytes for solid-state lithium-metal batteries.
Growing environmental concerns over petroleum-based plastics have increased interest in sustainable and biodegradable alternatives such as polyhydroxybutyrate (PHB). PHB is a naturally produced biopolymer synthesized by microorganisms and is widely recognized for its biodegradability, biocompatibility, renewability, and thermoplastic properties. Despite these advantages, PHB use remains limited by brittleness, high crystallinity, low thermal stability, a narrow processing window, and high production costs. This review discusses the production, properties, biodegradation behavior, and applications of PHB, with a focus on strategies to improve its performance. Modification approaches, including copolymerization, polymer blending, filler reinforcement, plasticization, and hybrid composite formulation, are critically reviewed to evaluate their effects on the thermal, mechanical, and processing behavior of PHB-based materials. The review also highlights recent developments in additive manufacturing, particularly fused deposition modeling/fused filament fabrication (FDM/FFF) for the extrusion of biodegradable PHB composite filaments. In addition, the biodegradation of PHB under various environmental conditions, including soil, compost, freshwater, marine, aerobic, and anaerobic environments, are discussed. Current challenges, research gaps, commercialization barriers, and future opportunities related to sustainable feedstocks, advanced composites, additive manufacturing, and circular economy integration are addressed. Overall, PHB shows strong potential as a sustainable alternative for packaging, biomedical, agricultural, and three-dimensional (3D) printing applications.
Single-point incremental forming (SPIF) produces localized plastic deformation, resulting in thickness reduction, geometrical deviation, and microstructural evolution. To establish the relationship between forming quality and microstructural response, this study develops a cross-scale analysis framework integrating finite element simulation, Kocks-Mecking (K-M)-based statistically stored dislocation (SSD) density inference, metallographic observation and electron backscatter diffraction (EBSD) characterization. Applied to an Al 1060 truncated-cone part, the framework converts the simulated equivalent plastic strain (PEEQ) into SSD density via the K-M model calibrated using the Voce hardening model and the Taylor relation. The inferred SSD density distribution is then spatially correlated with thinning rate, geometrical deviation, grain size, grain-boundary misorientation, kernel average misorientation (KAM), and geometrically necessary dislocation (GND) density across different forming regions. The inferred SSD density rapidly approached a saturation level of 1.55 × 1013 m-2, while the high-SSD density region progressively expanded during forming. This regional evolution was qualitatively consistent with the EBSD observations. The average grain size decreased from 30.4 μm to 21.9 μm, and the medium-angle grain-boundary fraction increased from 10.3% to 34.5%. Regionally, thickness reduction correlates strongly with PEEQ accumulation, SSD storage, and grain refinement, whereas geometrical deviation is more closely related to early-stage deformation heterogeneity. These findings provide a physically based route for predicting and controlling SPIF accuracy.