Search Results (4,089)

This study examines the effects of three polymer binders—polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyacrylic acid (PAA) on the mechanical properties and dry–wet cycle corrosion resistance of cement mortar at different dosages (1–4%). Mechanical testing combined with scanning electron microscopy (SEM) and molecular dynamics (MD) simulations was conducted to validate the experimental findings and reveal the underlying mechanisms. Results show that polymers reduce early-age strength but improve flexural performance, and at low dosage, enhance compressive strength. PVA and PAA exhibited a pronounced improvement in mechanical strength while PVA and PEG showed a significant improvement in wet cycle corrosion resistance. SEM observations indicated that polymers encapsulate cement particles, enhancing interfacial bonding while partially inhibiting hydration. MD simulations revealed that PVA and PAA interact with Ca²⁺ via Ca-O coordination, while PEG primarily forms hydrogen bonds, resulting in distinct water-binding capacities (PEG > PVA > PAA). These interactions explain the enhanced mechanism of mechanical and dry–wet cycle resistance properties. This work combined experimental and molecular-level validation to clarify how polymer–matrix and polymer–water interactions govern mechanical and durability, respectively. The findings provide theoretical and practical guidance for designing advanced polymer binders with tailored interfacial adhesion and water absorption properties to improve cementitious materials. Full article

This study prepared alkali-activated cementitious composites using high-whiteness kaolin, sodium water glass, and NaOH as the main raw materials. Multiple methods, including FE-SEM, XRD, whiteness/light transmittance tests, shrinkage rate measurements, DSC-TG, flexural strength testing, and hydrolysis resistance testing, were used to investigate the effects of curing temperature and time on material properties. The optimal parameters were determined as kaolin calcined at 1100 °C, activator modulus 1.25, calcined kaolin-to-activator ratio 1:1, and 2.5% deionized water added for molding. The optimal sample achieved a flexural strength of 23.81 MPa, with the bonding strength to porcelain 60.17 times that of gypsum and 1.90 times that of kaolin-bonded materials. Curing below 100 °C slowed polymerization, while temperatures exceeding 100 °C accelerated it, with violent reaction at 120 °C. Curing beyond 10 h reduced flexural strength. A large number of cage-like, ‘zeolite-like’ structures formed, closely relating to material properties. This study provides references for ceramic restoration materials. Full article

Background: Three-dimensional (3D) printing has emerged as a valuable tool in dentistry for producing provisional restorations with high precision and reduced costs. However, the limited mechanical strength of temporary 3D-printed resins remains a clinical concern. This in vitro study aimed to enhance the mechanical properties of a 3D-printed temporary resin by incorporating functionalized niobium (Nb) nanoparticles and to compare its performance with a conventional resin composite and a permanent 3D-printed resin. Methods: Six groups were evaluated: bisacrylic resin (Protemp), resin composite (Z350), temporary 3D resin (Temp 3D), permanent 3D resin (Perm 3D), Temp 3D + 0.05% Nb, and Temp 3D + 0.1% Nb. Niobium oxyhydroxide nanoparticles were synthesized using a hydrothermal method, silanized, and incorporated into the Temp 3D at 0.05% and 0.1% by weight. The tested variables included flexural strength (FS), elastic modulus (EM), surface hardness (SH), and color stability (ΔE). Results: The Z350 resin showed the best mechanical results. The addition of 0.1% Nb nanoparticles significantly improved the FS, EM, and SH of the Temp 3D, reaching values comparable to the Perm 3D (p > 0.05). Color stability remained unaffected across all groups. Conclusions: These findings suggest that Nb reinforcement at a low concentration is a promising strategy for improving the performance of 3D-printed temporary restorations. Full article

Ultra-high-performance concrete (UHPC) is increasingly employed in long-span and heavily loaded structural applications; however, the accurate prediction of its flexural capacity remains a significant challenge because of the complex interactions among geometric parameters, reinforcement details, and advanced material properties. Existing design codes and single-architecture machine learning models often struggle to capture these nonlinear relationships, particularly when experimental datasets are limited in size and diversity. This study proposes a compact hybrid CNN–Transformer model that combines convolutional layers for local feature extraction with self-attention mechanisms for modeling long-range dependencies, enabling robust learning from a database of 120 UHPC beam tests drawn from 13 laboratories worldwide. The model’s predictive performance is benchmarked against conventional design codes, analytical and semi-empirical formulations, and alternative machine learning approaches including Convolutional Neural Networks (CNN), eXtreme Gradient Boosting (XGBoost), and K-Nearest Neighbors (KNN). Results show that the proposed architecture achieves the highest accuracy with an R² of 0.943, an RMSE of 41.310, and a 25% reduction in RMSE compared with the best-performing baseline, while maintaining strong generalization across varying fiber dosages, reinforcement ratios, and shear-span ratios. Model interpretation via SHapley Additive exPlanations (SHAP) analysis identifies key parameters influencing capacity, providing actionable design insights. The findings demonstrate the potential of hybrid deep-learning frameworks to improve structural performance prediction for UHPC beams and lay the groundwork for future integration into reliability-based design codes. Full article

This study examines the effects of incorporating recycled carbon fibers obtained from decommissioned wind turbine blades into cementitious composites. An extensive experimental program was carried out, varying fiber content (0–8 kg/m³), fiber length (25, 38, 50 mm), water-to-cement ratio (0.4, 0.5), and cement type (CEM I 42.5, CEM II 42.5R/A-V). The mechanical properties of the fiber-reinforced concretes, including compressive strength, flexural strength, splitting tensile strength, and modulus of elasticity, were evaluated. The addition of recycled carbon fibers significantly improved flexural and splitting tensile strengths, with increases exceeding 60% and 100%, respectively, at the highest fiber dosage (8 kg/m³), attributed to efficient crack-bridging capability. Compressive strength was mainly influenced by the water-to-cement ratio, while the modulus of elasticity showed slight reductions in some mixes due to fiber clustering and increased micro-porosity. Regression analysis indicated that shorter fibers (25 mm) were more effective in enhancing flexural strength, whereas longer fibers (50 mm) improved splitting tensile strength. Classical predictive models generally underestimated the flexural capacity of recycled-carbon-fiber-reinforced concretes, highlighting the need for recalibration. Optical microscopy confirmed uniform fiber dispersion at lower dosages and a dominant pull-out failure mechanism. The findings demonstrate the feasibility of using recycled carbon fibers to enhance the mechanical performance of concrete while supporting sustainability through waste diversion and circular economy strategies. Full article

Port maintenance causes large quantities of dredged sediment throughout the world. The disposal of this material in authorised landfills is economically disadvantageous, as well as being at odds with a circular economy model with a reduced impact on the environment. The application of stabilization/solidification treatment to dredged marine sediments allows an improvement of their physical and mechanical properties, together with the production of cement-based materials that can be used for road construction, as well as for making blocks and bricks. In this study, an experimental laboratory investigation is carried out on two samples of sandy sediments collected from the Mola di Bari harbour (Southern Italy), to identify sustainable management options for recovering materials that will be dredged. To assess the influence on mortars made from sediments with variable organic matter content and seawater, these were characterised from a chemical–physical point of view before and after washing treatment and oxidative processes. The products of the Stabilization/Solidification (S/S) treatment were evaluated in terms of workability, flexural and compressive strengths, and, furthermore, a microstructural study was conducted using SEM-EDX and optical microscopy to analyse the internal structure of the materials. The mechanical performance evaluation clearly demonstrated organic matter’s negative impact on strength development, resulting in a 16% reduction. Pre-treatments, such as sediment washing, effectively improved the performance of treated sediments (e.g., 24% increase in compressive strength). This study aims to demonstrate the benefits of recycling marine sediments in cement-based materials, highlighting how this process can enhance circularity and sustainability while reducing the environmental impact of dredging activities. Full article

This study explored the use of Borassus fruit fiber as reinforcement for earthen matrices (BFRC). The experimental results of the testing carried out on the structural properties were used to generate a primary dataset for training and testing machine learning (ML) models. Linear regression (LR), Decision tree regressor (DTR), and gradient boosting regression (GBR) were used to build an ensemble learning (EL) model during the prediction of the hygroscopic properties, Young’s modulus, and compressive strength of the BFRC. Fiber content, activation concentration, curing days, dry weight, saturated weight, mass, flexural vibration, longitudinal vibration, correction factor, maximum load, and cross-sectional area were the various inputs considered in the structural properties prediction. The performance of both EL and single models (SMs) was appraised via three performance metrics—mean square error (MSE), root mean square (RMSE), and the coefficient of determination (R²)—to comparatively ascertain the model’s efficiency. Results showed that all models exhibited high accuracy in predicting Young’s modulus and compressive strength. Ensemble learning outperformed single models in predicting these properties, with MSE, RMSE, and R² of 0.01 MPa, 0.1 MPa, and 99% and 3,923,262.5 MPa, 1980.7 Pa, and 99% for compressive strength and Young’s modulus, respectively. However, for hygroscopic behavior, linear regression (LR) demonstrated superior performance compared to other models, with MSE, RMSE, and R² values of 0.13%, 0.36%, and 99%. Full article

Background: The addition of chlorhexidine in dental restorative materials is a promising strategy to reduce the recurrence of tooth decay lesions. However, the main challenge is to develop materials with antimicrobial activity in the long term. Objective: This study analyses the effect of filler type and concentration of resin composites supplemented with chlorhexidine loaded in carrier montmorillonite particles (MMT/CHX) regarding their chemical, physical, and short- and long-term antimicrobial proprieties. Materials: Experimental composites were synthesized with 0, 30, or 60% filler in two ratios, 70/30 and 80/20, of barium glass/colloidal silica, respectively, and 5 wt% MMT/CHX. Conversion was measured using near Fourier-transform infrared spectrometry. Sorption and solubility were determined by specimen weight before and after drying and immersing in water. Flexural strength (FS) and elastic modulus (E) were determined by three bending tests using a universal test machine. Chlorhexidine release was monitored for 50 days. Streptococcus mutans UA159 was used in all microbiological assays. Inhibition halo assay was performed for 12 months and, also, biofilm growth for the specimens and colony-forming unit (CFU). Remineralization assay was used on restored teeth using measurements of microhardness Knoop and CFUs. Results: Conversion, sorption, and solubility were not affected by filler type and concentration. FS and E increase with the filler concentration, independent from filler type. Chlorhexidine was significantly released for 15 days for all experimental materials, and the increase in filler concentration decreased its release. Halo inhibition was observed for a longer time (12 months) in materials with 60 wt% filler at 70/30 proportion. Also, 60 wt% filler materials, independent from the filler ratio, reduced the CFU in relation to the control group from 8 to 12 months. In the remineralization assay, besides the absence of differences in hardness among the groups, after biofilm growth, the CFU was also significantly lower in materials with 60 wt% filler. Conclusions: Materials with 60% filler, preferentially with 70% barium glass and 30% silica, and 5% MMT/CHX particles demonstrated long-term antimicrobial activity, reaching 12 months of effectiveness. Also, this formulation was associated with higher mechanical properties and similar conversion, sorption, and solubility compared to the other materials. Full article

A novel structure–functional-integrated particle featuring dual micromechanical interlocking property with resin matrix was constructed through surface modification of urchin-like serried hydroxyapatite (UHA) in this work, and the effect of this modification strategy on physicochemical and biological properties of dental resin composite was also investigated. A porous silica coating layer was anchored onto UHA surface via a simple template method in an oil−water biphase reaction system, and the coating time had a prominent effect on the coating thickness and morphology-structure of the particle. When these particles with different porous silica coating thickness were used as fillers for dental resin composite, results showed that UHA/PS5 (porous silica coating reaction time: 5 h) exhibited the optimal 3D urchin-like structure and a desirable porous silica coating thickness. Additionally, UHA/PS5 formed the best dual physical micromechanical interlocking structure when mixing with resin matrix, making the dental resin composites presented the desirable matrix/filler interfacial bonding, and the excellent physicochemical–biological properties, especially for flexural strength and water sorption-solubility. In vitro remineralization and cellular biological properties confirmed that the coating layer did not compromise their remineralization activity. The use of UHA/PSx provides a promising approach to develop strong, durable, and biocompatible DRCs. Full article

Geopolymers represent an innovative and environmentally sustainable alternative to traditional construction materials, offering significant potential for reducing anthropogenic CO₂ emissions. Among these, phosphoric acid-activated metakaolin-based systems have attracted increasing attention for their chemical and thermal resilience. In this study, we present a comprehensive structural and mechanical evaluation of metakaolin-based geopolymers synthesized across a wide range of Al/P molar ratios (0.8–4.0). Six formulations were systematically prepared and analyzed using X-ray powder diffraction (XRPD), small-angle X-ray scattering (SAXS), Fourier-transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (ssNMR), and complementary mechanical testing. The novelty of this work lies in the integrated mapping of composition–structure–property relationships across the broad Al/P spectrum under controlled synthesis, combined with the rare application of SAXS to reveal composition-dependent nanoscale domains (~18–50 nm). We identify a stoichiometric window at Al/P ≈ 1.5, where complete acid consumption leads to a structurally homogeneous AlVI–O–P network, yielding the highest compressive strength. In contrast, acid-rich systems exhibit divergent flexural and compressive behaviors, with enhanced flexural strength linked to hydrated silica domains arising from metakaolin dealumination, quantitatively tracked by ²⁹Si MAS NMR. XRPD further reveals the formation of uncommon Si–P crystalline phases (SiP₂O₇, Si₅P₆O₂₅) under low-temperature curing in acid-rich compositions. Together, these findings provide new insights into the nanoscale structuring, phase evolution, and stoichiometric control of silica–alumino–phosphate geopolymers, highlighting strategies for optimizing their performance in demanding thermal and chemical environments. Full article

Achieving the close packing and interlocking of coarse aggregates in concrete enhances the elastic modulus, thereby reducing deformation, and can improve the overall stiffness of concrete structures. This study focuses on reinforcing and toughening concrete with close-packing aggregate with silica fume and micro-steel fibers, and investigates its durability properties, including long-term mechanical performance, water absorption, and sulfate erosion resistance under dry–wet cyclic exposure. The experimental results indicate that the 360-day long-term compressive strength of the concrete reaches up to 109.3 MPa, and the 360-day flexural strength reaches 11.62 MPa. The addition of silica fume effectively reduces the water absorption of concrete with close-packing aggregate and improves its sulfate erosion resistance under dry–wet cycles. The lowest 28-day water absorption rate is 2.41%, and after 150 cycles of sulfate erosion, the compressive strength corrosion resistance coefficient of the concrete can be maintained at up to 68.4%, while the sulfate erosion resistance grade reaches up to KS120. The concrete overall exhibits excellent durability properties. Moreover, this is beneficial for enhancing the concrete’s performance under dry–wet cycles and its resistance to the effects of sulfate attack. Full article

Reinforced concrete is the most widely utilized building material for bridges, buildings, and other infrastructure components, and its longevity is significantly influenced by corrosion or rust. Corrosion shortens reinforced concrete’s service life and safety, which raises maintenance expenses. Concrete is a porous material that allows air and water to pass through, and corrosion begins when the air and water reach the steel. This study evaluated the mechanical and corrosion resistance properties of reinforced concrete containing recycled and supplemented cementitious materials. The results showed that mixtures containing fine glass aggregate, glass powder, slag, fly ash, or silica fume significantly improved the compressive, tensile, and flexural strengths, but the 10% slag mix, and 5% glass aggregate with 10% glass powder with 10% fly ash mix produced the best results overall. In addition, the mixture containing 15% fly ash produced the best result against corrosion. The corrosion tests revealed that mixtures with 10% slag and 20% glass powder also significantly enhanced the corrosion resistance of steel with the same results, confirming their effectiveness in reducing the permeability and increasing the durability of reinforced concrete. Full article

Ultra-high-performance concrete (UHPC) exhibits significantly superior compressive and tensile properties compared to conventional concrete, demonstrating substantial application potential in bridge engineering. This study conducted full-scale bending tests on a 30 m prestressed UHPC-NC composite box girder within an actual engineering context. The testing flexural capacity $M_t=\mathrm{34,469.2} \mathrm{k}\mathrm{N}·\mathrm{m}$ exceeded the design requirement $M_d=\mathrm{18,138.0} \mathrm{k}\mathrm{N}·\mathrm{m}$, with $M_t/M_d=1.90$. Finite element modeling (FEM) was employed to analyze and predict experimental outcomes, revealing a simulated flexural capacity of approximately 37,597.1 $\mathrm{k}\mathrm{N}·\mathrm{m}$. The finite element models further explored failure mode transitions governed by the loading position while the concentrated load-to-support distance exceeds 9.62 m (shear span to effective depth ratio λ = 6.3), and the box girder fails in flexure; while less than 9.62 m, the box girder fails in shear. The flexural capacity of the test girder was also estimated using Response-2000 software and the recommended formulas from the Chinese code T/CCES 27-2021 (Technical specification for ultra-high-performance concrete girder bridge). The Response-2000 software yielded a flexural capacity estimate of $M_r=\mathrm{30,816.1} \mathrm{k}\mathrm{N}·\mathrm{m}$. The technical specification provided two estimating results: (with safety factors) $M_{u1}=\mathrm{25,414.4} \mathrm{k}\mathrm{N}·\mathrm{m}$ and (without safety factors) $M_{u2}=\mathrm{33,810.9} \mathrm{k}\mathrm{N}·\mathrm{m}$. All estimated values of Response-2000 and Chinese code were rationally conservative ($M_r,{ M}_{u1}, M_{u2}<M_t$). Comparative analysis demonstrates that Abaqus FEM accurately simulates the flexural behavior of the prestressed UHPC-NC composite box girders. Both Response-2000 calculations and the Chinese code T/CCES 27-2021 provide critical references for similar applications of prestressed UHPC-NC composite box girders. Full article

To investigate the potential of metakaolin (MK) (5%, 10%, 15%, and 20% substitution of cement mass) and basalt fibre (volume contents of 0.1%, 0.2%, and 0.3%) in recycled aggregate concrete (RAC) products, RAC’s mechanical properties were first assessed with a singular incorporation of MK. The findings demonstrated that adding 15% MK optimised the compressive strength and flexural strength of RAC (at the recycled aggregate replacement levels of 30%, 45%, and 60% by weight). An orthogonal test was conducted to investigate the synergistic effect of MK and basalt fibre (BF), with the recycled coarse aggregate (RCA) replacement rate (mass ratio of RCA to natural coarse aggregates), MK content (cement mass substitution percentage), and BF content (volume dosage) identified as the influencing parameters. The variance analysis reveals that the influence of the replacement ratio of RCA on compressive strength surpasses that of MK content, which in turn exceeds that of BF content. Conversely, as for the flexural strength, BF is substantially more effective than that of MK. A model test of RAC curbs was performed based on the ideal mix ratio suggested by the single mixing of MK and MK and BF compound mixing inside the orthogonal test. The results demonstrate that the RAC curbs, with an RCA replacement rate of 30%, display optimal mechanical properties when 15% MK and 0.2% BF are incorporated. This surpasses the performance of 15% MK alone and illustrates that the mix incorporation of MK and BF is superior to that of MK alone. Full article

The present work investigates the influence of natural rubber (NR) on the mechanical properties and free vibration characteristics of elastomer-embedded NR-filled GFRP laminates for anti-vibration (AV) mounts. The tensile, flexural, and impact strength values of the preferred hybrid laminates are evaluated as per ASTM standards. To estimate vibration characteristics such as the modal frequency and damping of the hybrid laminates, a free vibration study is carried out under the fixed-free boundary condition. Based on the experimental results, the effect of NR filling in an epoxy matrix of elastomer-centric GFRP laminates is thoroughly investigated for its application in AV mounts. Full article