Search Results (503)

Hydrated lime is widely incorporated into cement-based mortars to improve workability and fresh-state properties; however, its influence on hydration products and mechanical performance remains insufficiently understood. This study investigates the effect of hydrated lime content on the mechanical behavior and microstructural development of cement-based mortars after 28 days of curing. Eight mortar formulations, ranging from lime-free (1:0:6) to lime-rich (1:5:6) mixtures, including intermediate and modified proportions, were evaluated through compressive strength, flexural tensile strength, and consistency tests. The microstructural evolution was investigated using complementary techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG/DSC), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS). Increasing hydrated lime content improved mortar workability but was generally associated with reduced compressive strength under the curing conditions investigated. The combined characterization techniques indicated progressive modifications in the hydration products and phase assemblage, with increased calcium-rich phases, greater evidence of carbonation, and reduced continuity of the hydraulic matrix as the hydrated lime content increased. The observed microstructural changes were qualitatively consistent with the mechanical behavior of the mortars. The conclusions of this study are restricted to the 28-day curing period investigated, and further research is required to evaluate the long-term influence of hydrated lime on carbonation and durability-related properties. These findings contribute to a better understanding of the role of hydrated lime in cement-based mortars and provide experimental evidence for the optimization of mortar formulations. Full article

Corrosion of reinforcing steel and degradation of concrete caused by chloride penetration are the most critical forms of durability failure in marine environments. This requires that repair materials possess both high impermeability and stable chemical binding capacity. In this study, the impact patterns of sulfoaluminate cement (SAC) dosage on the chloride erosion durability of an OPC-GGBS-SAC ternary repair system were systematically evaluated. Through chloride ion binding capacity tests, electrical flux experiments, and microscopic analytical techniques including XRD, DTG and SEM-EDS, the synergistic regulation mechanisms of the dual functions of ‘physical barrier’ and ‘chemical binding’ in the composite material were elucidated. The findings show that the performance of the composite material was optimal at an SAC content of 10%. The electrical flux of composite materials at 28 d was 28.9% lower than that of the OPC system, whilst the chloride ion binding rate increased by 3.92%. Microstructural analysis indicates that an appropriate amount of SAC promoted the generation of ettringite (AFt) to optimize the early-age pore structure and stimulated the production of more C-S-H gel and AFm phases, thus synergistically enhancing impermeability and chemical binding capacity. When the SAC content exceeded 10%, excess gypsum inhibited the formation of AFm. Moreover, the concentration of early-stage hydration led to microdefects, resulting in a decline in durability. This study identifies the optimal dosage of SAC in the ternary system and clarifies the underlying mechanism, thereby providing a scientific basis for designing high-durability repair materials suitable for harsh ocean conditions. Full article

Loess has a metastable microstructure and high water sensitivity. When exposed to water, it undergoes rapid structural damage and disintegration, posing significant risks to the stability and durability of geotechnical structures such as foundations and slopes. Unconfined compressive strength (UCS) tests, direct shear tests, uniaxial tensile strength tests, and slake durability tests were conducted to evaluate the treatment performance. Optical microscopy and SEM were used to characterize the changes in microstructure to explain the potential reinforcement mechanism. The results show that microbial-induced carbonate precipitation (MICP) treatment leads to substantial improvement. Compared with untreated loess, the UCS, cohesion, internal friction angle, and uniaxial tensile strength increased by 370%, 663%, 43.7%, and 480%, respectively. Empirical refinements to the Mohr-Coulomb criterion were established to relate the measured UCS and uniaxial tensile strength to their theoretical values predicted from cohesion and friction angle. Both correlation models achieved R² > 0.82, quantifying the additional structural strength contributed by bio-cementation. At the same time, the treatment significantly improved water stability, and the slaking index was reduced from 100% to less than 20%. Microstructural analysis shows that precipitated calcium carbonate crystals bond soil particles at contact points and fill inter-particle pores, constructing a bonding framework, which enhances the mechanical strength and water stability of the soil mass. These research results further illustrate the potential of MICP in enhancing the performance of loess in engineering projects. Full article

Encapsulation serves as a critical strategy for the preservation of sensitive bioactive compounds, ensuring their stability and functionality within complex food matrices. Cellulose nanocrystals (CNCs) upcycled from by-products are being favoured as wall materials because they offer a sustainable yet powerful solution for maintaining compound stability. This study evaluated the encapsulation of fish oil (FO) within a nanocomposite matrix of garlic skin-derived cellulose nanocrystals (GCNCs) and soy protein isolate (SPI). The synergistic effects of FO loading and GCNC:SPI ratios on the microcapsules’ structural, physicochemical, and digestive properties were investigated. Higher FO loading significantly reduced the moisture content of the resulting microcapsule powders while increasing bulk and tapped densities by minimising internal porosity. Microstructural analysis showed irregularly shaped agglomerates. Higher FO loading also increased surface oil retention and inter-particle adhesion of the microcapsule powders; however, elevated SPI levels effectively counteracted these effects. Colour analysis further revealed that higher FO loading reduced powder lightness (L*) and increased yellowness (b*), while greater GCNC content positively influenced redness (a*). The formulation containing 10% FO, 3% GCNCs, and 7% SPI was identified as the optimal treatment. This ratio achieved the highest encapsulation efficiency (65.77% ± 1.10) and demonstrated superior flowability, characterised by the lowest Carr’s Index (20.65% ± 0.29) and Hausner Ratio (1.23 ± 0.05). Additionally, it maintained oxidative stability, with TBARS values (2.42 ± 0.08 mg MDA/kg oil) remaining consistently below the established 3 mg MDA/kg threshold. Fourier Transform Infrared Spectroscopy confirmed the successful entrapment of FO within the GCNC–SPI matrix. According to the in vitro digestion assays, the wall material provided a durable barrier in acidic media because the gastric release (28.04–55.28%) was significantly lower than the intestinal release (64.38–77.62%). The predominant fatty acids identified in both encapsulated and unencapsulated products were myristic acid (saturated fatty acid), elaidic acid (monounsaturated fatty acid), and docosadienoic acid (polyunsaturated fatty acid). Superior nutritional quality index (NQI) values in the encapsulated samples underscore the effectiveness of the wall material in providing a critical defence against fatty acid degradation and preserving overall oil quality. These findings suggest that the GCNC/SPI binary system is a highly effective delivery vehicle for protecting sensitive polyunsaturated fatty acids in functional food applications. Full article

The huge demand for natural sand in the global construction industry has caused resource shortages and severe environmental issues. Meanwhile, China produces massive annual iron tailings, and their stockpiling poses prominent potential safety hazards. At present, numerous investigations have been carried out on the fundamental properties of concrete prepared by replacing natural sand with iron tailings sand (ITS). However, most studies are limited to single replacement ratios and conventional strength mix proportions. Systematic research focusing on high-replacement-ratio systems, long-term durability performance, and supporting practical construction technologies for engineering applications remains insufficient. Obvious gaps still exist regarding the key mechanisms and practical operation standards for high-value and large-scale utilization. Against this background, this paper prepares concrete with three strength grades (C30, C40, C50) and six ITS replacement ratios (0%, 20%, 40%, 60%, 80%, 100%). Cube compressive tests and prism axial compressive tests are conducted, combined with SEM microscopic microstructure analysis. Axial compression tests and bearing capacity research are further carried out on reinforced concrete short columns (RCSC) with the optimal replacement ratio. The results show that concrete compressive strength increases first and then decreases with the rise in iron tailings sand concrete (ITSC), with 60% identified as the optimal replacement ratio. At this ratio, the compressive strength of C30, C40 and C50 concrete increases by 24.3%, 11.5% and 12.9%, respectively, while the bearing capacity of short columns rises correspondingly by 18%, 14.1% and 8.1%. Microscopic test results reveal that ITS exerts both physical filling and chemical active effects. Its fine particles fill internal pores inside the matrix and refine the pore structure. Meanwhile, the reactive mineral components contained in ITS can participate in the hydration reaction of the cementitious system, accelerate the hydration rate and generate more dense hydration products. Therefore, ITS facilitates the hydration process and improves the mechanical properties of concrete. A calculation method for the axial bearing capacity of RCSC incorporating ITS is proposed via theoretical analysis. This study provides a theoretical basis for preparing concrete by replacing natural sand with ITS. Using ITS as aggregate is expected to alleviate tailings stockpiling risks, reduce natural sand consumption, and realize solid waste resource recycling. It also offers valuable references for the green development of the construction industry and safety protection in mining areas. Full article

The accumulation of waste tyres presents a significant environmental challenge owing to their non-biodegradable nature and limited recycling options. The incorporation of tyre-derived rubber into concrete offers a promising strategy to reduce landfill waste and lower the consumption of natural aggregates. This study presents an integrated experimental and machine learning-based framework for evaluating and predicting the performance of rubberized concrete. M25-grade concrete mixtures were prepared with partial replacement of coarse aggregates by waste tyre rubber at proportions of 0%, 10%, 20%, and 30% by volume. Mechanical performance was assessed through compressive and split-tensile strength tests, whereas durability was evaluated using water absorption measurements. Microstructural characterization was conducted using scanning electron microscopy and X-ray diffraction analysis. In parallel, predictive models based on artificial neural networks, adaptive neuro-fuzzy inference systems, and fuzzy logic were developed and validated using statistical measures. The results showed that increasing rubber content reduced mechanical strength and increased water absorption due to weaker interfacial bonding and higher porosity. Nevertheless, concrete containing a 10% rubber replacement retained approximately 90% of the control strength while maintaining satisfactory durability. The machine learning models demonstrated strong predictive accuracy for estimating concrete properties. Overall, the findings suggest that limited incorporation of waste tyre rubber can contribute to the development of sustainable and low-carbon concrete materials with reduced embodied energy and environmental impact. Full article

Municipal solid waste incineration (MSWI) fly ash contains soluble salts and heavy metals, which may cause leaching risks and durability deterioration when directly used in cement-based materials. This study aimed to investigate the synergistic effects of carbonated and hydrophobically modified municipal solid waste incineration fly ashes on the engineering performance and heavy-metal immobilisation of mortar. Mortars containing modified fly ashes were evaluated in terms of hydration behavior, compressive strength, water absorption, electrically accelerated corrosion resistance, heavy metal leaching, and microstructure. Carbonated fly ash promoted hydration through the nucleation and filling effects of CaCO₃, shortened setting time, increased cumulative hydration heat, and improved compressive strength by up to 4.5 MPa. Hydrophobic fly ash reduced particle wettability and capillary water transport, thereby reducing water uptake and mitigating visible corrosion-induced deterioration under accelerated conditions, although excessive dosage delayed hydration and reduced strength. The combined modification showed a clear synergistic effect, reducing water absorption by up to 39.9%. In particular, the C3H3 specimen, containing 75 kg·m⁻³ carbonated MSWI fly ash and 75 kg·m⁻³ hydrophobically modified MSWI fly ash, exhibited the lowest water absorption of 3.92% and effectively suppressed crack propagation and corrosion-product migration. The leaching concentrations of Cr, Cu, Zn, As, Cd, and Pb were below the GB 18598—2019 limits. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and low-field nuclear magnetic resonance (NMR) results indicated that the improved performance originated from a composite barrier involving carbonate filling, hydrophobic interfacial blocking, and heavy metal solidification/stabilization. Full article

To address early-age cracking in concrete walls of hydraulic structures such as ship locks, basalt fibers (BFs) were incorporated as a reinforcement strategy. The effects of varying BF dosages and lengths on the workability, mechanical strength, and crack resistance of concrete were systematically evaluated. Furthermore, the internal microstructure was examined using scanning electron microscopy (SEM), and the durability performance, including impermeability, freeze–thaw resistance, and abrasion resistance, was assessed. The results indicate that workability decreased with increasing fiber content and length. The highest mechanical performance among tested mixes was achieved with 0.1% BF of 9 mm length, increasing 7-day and 28-day compressive strength by 17.47% and 22.59%, respectively, compared to plain concrete. The greatest crack resistance was observed with 0.2% BF of 18 mm length, delaying cracking by 150% and reducing crack width by 85%. Durability tests showed that a 0.2%-18 mm BF mix reduced water permeability depth by 47.37% and a 0.3% BF content optimized abrasion resistance. Freeze–thaw cycles indicated that a 0.3% fiber content effectively maintained the relative dynamic elastic modulus. SEM analysis revealed that BFs act as micro-bridges within the matrix, optimizing pore structure, inhibiting micro-crack propagation, and enhancing concrete density. This study evaluates BF-reinforced concrete and provides a practical reference for improving crack resistance and long-term durability in ship lock structures. Full article

Traditional research was mostly focused on the effects of emulsions on the mechanical properties and durability of cement mortar, while studies on the regulation mechanism of emulsions on the rheological properties of cement-based materials and the coupling mechanism with the hydration process were rarely conducted. In this paper, a novel core–shell structured emulsion was prepared by free radical polymerization. The regulation of cement mortar yield stress, creep recovery, dynamic viscosity, and thixotropy by different dosages (0–10%) of the emulsion admixture was systematically investigated, and combined with characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), the microscopic action mechanism of the emulsion was elucidated. It was demonstrated that the Bingham fluid behavior of cement mortar was not altered by the core–shell emulsion, whereas a significant dosage-dependent regulatory effect on its rheological parameters was observed, and a critical regulation interval of 4–6% was identified. At an emulsion dosage of 10%, the yield stress of the mortar was increased by 937.0% compared to that of the control group. At dosages of 2–4%, the static structural stability and construction flowability of the mortar were synergistically optimized, and the weakest thixotropy and the best structural stability were exhibited at an emulsion dosage of 4%. A more pronounced shear-thinning behavior was shown by all modified mortars, and their high-shear flowability was not affected. Microstructural analysis confirmed that no chemical reaction occurred between the emulsion and the cement hydration products. Through the triple effects of “hydration retardation by physical coating, pore filling and densification, and composite network enhancement”, a film was formed on the surface of cement particles by the emulsion, which hindered the diffusion of water and ions, thereby regulating the cement hydration process and microstructural evolution. Full article

Saline-affected soils exhibit poor mechanical properties and are prone to durability degradation under environmental disturbances, severely hindering infrastructure development in saline-affected regions. This study adopted a synergistic consolidation treatment for sulfate-salinized soils using a guar gum (GG) and Portland cement composite system, formulating 25 mix designs with GG content ranging from 0% to 2% and cement content from 0% to 12%. The unconfined compressive strength (UCS), dry–wet cycle durability, and repeated load fatigue performance of the stabilized soils were systematically tested. Combined with microstructural characterization techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and CT scanning, the evolution patterns of the solidified soil’s mechanical properties and the macro-micro interaction mechanisms were revealed. Results indicate that cement is the primary strength source in cement-stabilized soil: at a cement dosage of 12%, the UCS reaches 2.53 MPa, a 41-fold increase compared to the native soil. A significant synergistic strengthening effect exists between cement and GG at the optimal GG dosage of 0.5%–1.0%, with the optimal mixture ratio being 6%–9% cement blended with 0.5%–1.0% GG. With this optimized ratio, the stabilized soil shows a strength retention rate of 87.2% after 10 dry–wet cycles, and its fatigue life extends to 1986 cycles (a 42.6% increase compared to pure cement-stabilized specimens). Microstructural analysis suggests that the stabilization process is fundamentally governed by interfacial micro-coating mechanisms. The reaction between cement aluminates and soil sulfates generates abundant ettringite, which is hypothesized to form a rigid skeletal framework. Simultaneously, GG forms a hydrogel network that acts as a dense, protective organic–inorganic micro-coating on the surface of soil aggregates and cement phases. This interfacial encapsulation optimizes the pore structure, reducing porosity to 1.43% and fundamentally blocking inward water infiltration pathways at the aggregate interface. However, excessive GG (>1.5%) coats cement particles, hinders hydration reactions and induces structural defects, ultimately leading to performance degradation. This study elucidates the macro-micro coupled mechanism of GG-cement composite consolidation for saline–alkali soils, providing theoretical foundations and technical solutions for saline–alkali soil consolidation engineering. Full article

The present study investigates the development of non-autoclaved aerated concrete (NAAC) incorporating rice husk ash (RHA)-derived amorphous silica, polypropylene microfibers, and a polycarboxylate-based superplasticizer to improve mechanical performance and durability while maintaining low density and thermal conductivity. Experimental investigations included density, compressive strength, thermal conductivity, water absorption, X-ray diffraction (XRD), microstructural observations, and TG–DTA analysis. The developed compositions containing 5–7% RHA and 0.10–0.20% polypropylene microfibers achieved compressive strength values of 4.5–4.8 MPa at densities of 520–560 kg/m³, which are comparable to or higher than values commonly reported for non-autoclaved aerated concrete of similar density. Thermal conductivity decreased to 0.12–0.13 W/(m·K), while water absorption was reduced to 15–18%. XRD, microstructural, and TG–DTA analyses suggested enhanced hydration reactions and improved development of the cementitious matrix due to pozzolanic interaction between amorphous silica and calcium hydroxide. The incorporation of polypropylene microfibers was associated with improved structural homogeneity of the developed NAAC compositions, whereas the superplasticizer enhanced mixture homogeneity and pore stability. The results suggest that the combined use of agricultural waste-derived silica and fiber reinforcement provides an effective approach for producing sustainable and energy-efficient NAAC without autoclave curing. Full article

The poor engineering properties of Gobi soil, such as low strength and poor water stability, pose challenges for foundations in arid regions, especially large photovoltaic plants. This study examines the effect of polypropylene (PP) fiber reinforcement on Gobi soil from Dabancheng, Xinjiang. Laboratory tests including unconfined compressive strength, direct shear (orthogonal experimental design), slake durability, and scanning electron microscopy were performed to investigate the influences of fiber length (6, 9, 12 mm), fiber content (0.3–1.1% by dry soil mass), and water content (4–12.5%). Results indicate that PP fibers change the failure mode from brittle to ductile. The optimal combination (9 mm fiber length, 0.7% content, and Proctor optimum water content of 10.5% corresponding to maximum dry density) improves cohesion by 122% (reinforcement coefficient K = 2.22). Moreover, fibers alter the disintegration behavior from complete to stable partial disintegration; the 12 h disintegration ratio decreases from 100% to 13% under optimal conditions. Microstructural analysis shows that an appropriate fiber content creates a uniform three-dimensional reinforcing network, enhancing mechanical interlocking and fiber bridging, whereas excessive fiber leads to agglomeration and increased pore connectivity, degrading overall performance. This study provides a low-carbon, sustainable soil stabilization method and practical design parameters for Gobi desert infrastructure. Full article

To investigate the corrosion resistance and deterioration mechanism of cast-in situ concrete incorporating iron ore tailings aggregate (IOT), specimens with IOT replacement ratios of 0%, 30%, and 50% were exposed to distilled water, endogenous Cl⁻-SO₄²⁻ corrosion, exogenous Mg²⁺-SO₄²⁻ corrosion, and endogenous-exogenous coupled corrosion. The evolution of mass, size, compressive strength, and flexural strength was evaluated, while Nuclear Magnetic Resonance (NMR), Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS), X-ray Diffraction (XRD), and Thermogravimetric Analysis/Derivative Thermogravimetry (TG/DTG) were used to characterize pore structure and phase transformation. Results show that distilled water causes limited variation, whereas exogenous and coupled corrosion accelerate product accumulation, size expansion, pore coarsening, and strength degradation. Under exogenous Mg²⁺-SO₄²⁻ corrosion, the peak compressive strengths of specimens with 0%, 30%, and 50% IOT reach 43.30 MPa, 45.60 MPa, and 46.93 MPa, respectively, with the 50% IOT specimen showing an 8.38% increase compared with the specimen without IOT. TG/DTG results show that the Ca(OH)₂ related mass loss decreases from 5.42% under distilled water immersion to 4.37% under exogenous Mg²⁺-SO₄²⁻ corrosion, confirming calcium consumption during sulfate–magnesium attack. Microstructural characterization reveals that sulfate reaction, chloride binding, and Mg²⁺-induced decalcification jointly promote the formation of gypsum, ettringite, Friedel’s salt, magnesium silicate hydrate (M-S-H), and magnesium-associated corrosion products. Overall, 30% IOT provides better pore refinement and mechanical stability under endogenous and exogenous corrosion, whereas 50% IOT improves residual skeleton support under coupled corrosion. These findings provide guidance for durability design and sustainable utilization of IOT aggregate in cast-in situ concrete. Full article

Copper and its alloys are widely used in electrical, automotive, aerospace, and energy applications because of their excellent thermal and electrical conductivity. However, the low hardness and poor wear resistance of pure Cu limit its use under tribologically demanding sliding conditions. In this study, Cu matrix composites reinforced with 1 wt.% boron carbide (B₄C), boron (B), chromium (Cr), cobalt (Co), alumina (Al₂O₃), and graphite (Gr) were fabricated by powder metallurgy and comparatively evaluated under identical processing and testing conditions. Phase constitution and microstructural characteristics were analyzed by XRD, SEM, and EDS, while mechanical and tribological behavior was assessed by Vickers hardness and dry sliding wear tests. All reinforcements improved the hardness of the Cu matrix compared with unreinforced Cu. The hardness increase followed the order Cu–B₄C (68.91%) > Cu–B (66.43%) > Cu–Gr (63.97%) > Cu–Al₂O₃ (61.79%) > Cu–Cr (42.69%) > Cu–Co (36.04%). Dry sliding wear tests, performed under a 10 N normal load, 0.05 m s⁻¹ sliding speed, and 1000 m sliding distance against a 316L stainless-steel ball, showed that all reinforced composites exhibited lower mass loss and more stable sliding behavior than pure Cu. Among all samples, Cu–B₄C displayed the best wear performance, with a 154.8% improvement in wear resistance relative to pure Cu. SEM analysis of the worn surfaces revealed that reinforcement addition reduced severe plastic deformation, groove formation, and delamination, leading to a more stable wear regime. Graphite- and boron-containing composites benefited from interfacial lubrication and contact stabilization, whereas B₄C and Al₂O₃ improved wear resistance through rigid-particle strengthening and enhanced load-bearing capacity. By comparing ceramic, metalloid, metallic, oxide, and solid-lubricating reinforcements at the same low addition level and under identical processing and testing conditions, this study provides a reinforcement-selection framework for Cu-based composites requiring improved hardness and dry-sliding durability. Full article

Ultra-high-performance concrete (UHPC) is known for its exceptional compressive strength and durability; however, its brittle nature requires fiber reinforcement to improve toughness and tensile performance. This study investigates the synergistic effects of triple fiber reinforcement, including desized and sized carbon fibers (0.2–1.0 vol%), steel fibers (1.0 vol%), and polypropylene fibers (0.2 vol%) on the fresh, mechanical, durability, microstructure, and fire resistance properties of UHPC. The experimental program included workability, compressive and flexural strength, load-deflection behavior, electrical resistivity, dynamic modulus of elasticity, SEM analysis, and fire resistance at elevated temperatures (425 and 900 °C). The results showed that desized carbon fibers performed better than sized fibers by improving workability, fiber dispersion, flexural behavior, and fiber–matrix bonding. The optimal triple-fiber composition, DC1.0P0.2S1.0, achieved the highest flexural strength of 24 MPa while maintaining compressive strength above 141 MPa. The triple-fiber system provided effective multi-scale crack control, where PP fibers prevented explosive spalling, carbon fibers bridged meso-crack control, and steel fibers enhanced macro-crack load transfer and ductility. SEM analysis further confirmed better dispersion and stronger interfacial bonding of desized carbon fibers. Overall, the optimized triple-fiber system significantly improved flexural performance, toughness, workability, and fire resistance without notably reducing compressive strength, demonstrating strong potential for advanced structural applications. Full article