Search Results (1,047)

Autogenous shrinkage is a key factor contributing to early-stage cracking in high-performance concrete (HPC), which significantly affects structural durability and service life. As core components of HPC, supplementary cementitious materials (SCMs) can significantly improve concrete workability, mechanical properties, and durability, as well as reduce the risk of shrinkage cracking in HPC, by regulating hydration kinetics, pore structure, and microstructural evolution. The primary objective of this review is to elucidate the differential mechanisms by which different active pozzolanic materials regulate the autogenous shrinkage of HPC. This paper elucidates the patterns and mechanisms by which typical SCMs in HPC (such as fly ash, slag, silica fume, limestone powder, and nano-silica) affect the autogenous shrinkage of HPC. It analyzes the influence of key factors—including the type of SCMs, dosage, particle characteristics, water-to-binder (w/b) ratio, and composite blending on the autogenous shrinkage of HPC. Research indicates that highly reactive SCMs (such as silica fume and nano-silica) accelerate the self-drying process and increase autogenous shrinkage, whereas low-reactivity SCMs (such as fly ash) suppress autogenous shrinkage through dilution effects and by prolonging the hydration cycle. The combined use of multiple SCMs can achieve synergistic control of autogenous shrinkage and mechanical properties. Furthermore, this paper reviews existing autogenous shrinkage prediction models that account for the influence of SCMs and outlines future research directions. At the same time, this review identifies the limitations that currently exist in the research: there is a lack of a unified quantitative theoretical framework for the synergistic effects of multicomponent admixtures. The applicability of prediction models under multi-field coupling of temperature, humidity, and corrosive media is limited. And there is insufficient experimental data on the long-term shrinkage behavior of new low-carbon admixtures such as rice husk ash and calcined clay, which requires further dedicated research. Full article

Water-retaining roller-compacted concrete (RCC) dams suffer severe deterioration under coupled moisture ingress and freeze–thaw (F-T) cycles. To elucidate the damage mechanisms, this study employed industrial X-ray computed tomography (CT) synchronized with uniaxial compression and acoustic emission (AE) monitoring. The cross-scale damage evolution of RCC was investigated under dry, water-saturated, 25, and 50 F-T cycle conditions. The results indicate the following: (1) Macroscopically, F-T damage causes linear peak stress attenuation, shifting the failure mode from brittle axial splitting to ductile oblique shear. (2) Mesoscopically, frost-heaving stress expands native mesopores (500–2500 μm), increasing their volume fraction from 8.45% to 14.86% and remodeling isolated voids into a 3D interconnected defect network. (3) Microscopically, GMM-based AE clustering reveals a fracture transition. Driven by moisture lubrication and defect propagation, global shear cracks surpass the 50% threshold at 25 cycles (53.5%), reaching 68.6% at 50 cycles. (4) For cross-scale mapping, calibrating the AE b-value via Aki’s method decouples pore-water signal attenuation. Its pre-peak characteristic (an initial decrease followed by a rebound) accurately maps microcracks unstably coalescing along interconnected pores to form macroscopic shear planes. This cross-scale mechanism provides a scientific paradigm for condition monitoring of massive concrete in cold regions. Full article

To investigate the elevated-temperature performance of Ultra-High-Performance Concrete (UHPC) and Ultra-High-Performance Geopolymer Concrete (UHPGC), a systematic comparative study was conducted at 800 °C. This study examined the effects of the steel fibre geometry (micro and hooked-end) and dosage (1.5% and 2.0%) on mass loss, crack propagation, residual compressive, flexural, and tensile strengths, and chemical evolution following a 24 h pre-drying protocol to mitigate explosive spalling. The results demonstrate that UHPGC exhibits superior thermal stability and residual mechanical performance compared with UHPC after high-temperature exposure. Among all mixtures, the UHPGC mixture reinforced with 2% micro steel fibres (UHPGC-M2) achieved the highest residual compressive strength (30 ± 0.4 MPa, corresponding to 25% strength retention compared with 21% for the equivalent UHPC mixture), the lowest post-exposure crack width (0.08 mm), and the highest tensile strength retention (17.9%). Micro steel fibres were more effective in controlling crack propagation and preserving peak load capacity, whereas hooked-end fibres contributed more significantly to post-peak ductility. Chemical analysis revealed substantial chemical changes in both systems after exposure to 800 °C. However, UHPGC exhibited lower mass loss (4.8%) and greater residual performance. These findings establish micro steel fibre-reinforced UHPGC as a sustainable and high-performance material for fire-resistant structural applications. Full article

This study investigates the effects of low-volume steel microfibers (0–0.4 vol.%) and superplasticizer (SP) dosage (0.8 wt.% and 1.5 wt.%) on the mechanical and durability properties of self-compacting concrete (SCC) for railing structures, with a constant water-binder ratio of 0.28. Fresh (slump flow), mechanical (compressive strength up to 90 days, 28-day flexural strength), durability (drying shrinkage, freeze–thaw resistance after 200 cycles), and microstructural (mercury intrusion porosimetry) properties were evaluated. SP enhances flowability while steel fibers reduce it. All mixtures except that with 0.8% SP and 0.4% fibers meet the workability requirements of Chinese standard JGJ/T 283-2012 for SCC. Compressive and flexural strengths generally increase with fiber content but decrease when the SP dosage rises from 0.8% to 1.5%. Steel fibers effectively reduce drying shrinkage and improve freeze–thaw resistance, as indicated by higher relative dynamic elastic moduli and lower mass loss after 200 cycles. Microstructural analysis reveals that the higher SP dosage (1.5 wt.%) significantly increases porosity, which explains the observed higher shrinkage and lower strength. Considering mechanical properties, durability, and castability, the SCC mixture with 0.3 vol.% steel fibers and 0.8 wt.% SP is recommended for railing structure applications. Full article

Global efforts to end hunger are about more than producing enough food; they are also about producing food that is nutritious enough. Micronutrient deficiencies—the “hidden hunger” affecting billions—persist in part because the domestication bottleneck quietly eroded mineral and lipid diversity from the very crops the world relies on most. Wild relatives of domesticated legumes still carry much of that diversity, and genetic biofortification offers a sustainable route to put it back to work. Wild Vigna germplasm remains poorly characterized for traits that could support nutritional biofortification and neo-domestication. With that in mind, we characterized the seed mineral and fatty acid composition of 86 accessions from four wild Vigna species (V. vexillata, V. ambacensis, V. reticulata and V. racemosa), benchmarked against three domesticated (cultivars) and semi-domesticated checks (V. unguiculata, V. umbellata and V. vexillata landrace). Copper, manganese, zinc and iron were quantified by flame atomic absorption spectrophotometry after dry-ash digestion, and fatty acids were profiled as methyl esters by GC-MS. The species differed systematically in their mineral profiles. V. reticulata stood out as the most promising donor for copper-focused breeding, V. vexillata carried the highest median Zn, Mn and Fe values and is attractive for multi-micronutrient improvement, V. ambacensis showed a more stable but less extreme profile, and V. racemosa combined a relatively high Fe concentration with the most nutritionally favorable lipid profile of all—dominated by the essential polyunsaturated linoleic (C18:2n 6) and α-linolenic (C18:3n 3) acids. The other three wild species, by contrast, were dominated by saturated palmitic (C16:0) and stearic (C18:0) acids, which gives their oils greater oxidative stability and different food-industry applications. Principal component analysis supported these patterns for both datasets—minerals (PC1 = 60.39%, PC2 = 20.21%; cumulative 80.61%) and fatty acids (PC1 = 81.6%, PC2 = 14.0%; cumulative 95.6%)—and cleanly separated V. racemosa and the checks from the remaining wild species on lipid composition. Together, these results identify concrete targets for marker-assisted biofortification and de novo domestication of four African Vigna taxa. Full article

The durability of marine concrete square piles is critically governed by chloride transport at the corners of piles, regions subject to multi-directional erosion and pronounced accumulation under cyclic wetting–drying conditions. In this study, we developed a two-dimensional coupled moisture–chloride convection–diffusion model for a quarter section of the corner of a square pile, incorporating the time-dependent surface chloride concentration and a nonlinear moisture diffusion coefficient. The governing equations were numerically solved using the unconditionally stable alternating direction implicit (ADI) finite-difference method, which effectively overcomes the instability issues inherent in long-term simulations of strongly coupled systems. Model predictions were validated against experimental data from the literature, showing good agreement. Parametric investigations revealed that (1) the effect of moisture–chloride coupling is significant, with a low initial degree of saturation intensifying capillary-driven convection and accelerating early-stage chloride ingress; (2) a higher water-to-cement ratio markedly increases pore connectivity, exacerbating chloride accumulation under bidirectional erosion; and (3) increasing the drying-to-wetting time ratio effectively reduces net chloride buildup by curtailing the total duration of immersion. These findings provide a theoretical foundation for durability design and service-life assessment regarding square pile foundations in marine tidal and splash zones. Full article

Reinforced concrete structures in marine environments are subjected to severe deterioration, particularly in tidal zones. The development of intrinsically hydrophobic concrete through internal modification provides a promising strategy to mitigate this challenge. This study employed sodium methyl silicate (SMS) as a hydrophobic agent to prepare recycled fine aggregate concrete (RFAC), which was subsequently subjected to accelerated indoor chloride dry–wet cycling. The deterioration behavior of RFAC and the degradation mechanism of the SMS-induced hydrophobic film during dry–wet cycling were investigated through evaluations of mechanical performance, hydrophobicity, chloride resistance, microstructure, phase composition, pore structure, chemical bonding, and functional groups. The results show that SMS improves the hydrophobicity of RFAC but inhibits its hydration process. The optimal SMS dosage for RFAC under dry–wet cycling is 9‰, which achieves a balance between hydrophobicity enhancement and pore structure optimization. Compared with ordinary RFAC, the specimen exhibits 12.9‰ and 17.6% increases in compressive strength and RDEM, respectively, after 30 cycles, accompanied by reductions of 25.8%, 52.7%, and 80.0% in peak free chloride content, chloride erosion depth, and convection zone depth, respectively. RFAC with 9‰ SMS exhibits a denser matrix with lower porosity and fewer corrosion products. SMS enhances chloride resistance mainly by reducing water transport and chloride ion ingress through hydrophobic modification. Dry–wet cycling gradually deteriorates the SMS-induced hydrophobic film through the weakening of Si-C-related structures, while the Si-O-Si framework remains relatively stable. A quantitative correlation between the contact angle and free chloride ion content is established, and the modified Lucas–Washburn equation provides a reasonable description of chloride ion penetration depth. Full article

Concrete structures are prone to cracking during service, and epoxy grouting is a widely adopted technique for structural intervention. However, the inherent brittleness and poor durability of neat epoxy under complex loading and environmental exposure remain critical challenges. This study systematically evaluates the mechanical performance of epoxy-grouted concrete interlayer systems modified by carbon fiber (CF), glass fiber (GF), and polyethylene microspheres (PE). A comprehensive experimental program was conducted, including compression, three-point bending, and Brazilian splitting tests at three loading angles, combined with digital image correlation for surface strain monitoring. The effects of grout thickness and wet–dry cycles were systematically investigated. Results demonstrate that reinforcement modification helps to improve the performance of grouted concrete, with optimal behavior highly dependent on loading mode. CF-reinforced specimens with strong interfacial bonding exhibit the highest compressive strength, which is 150% higher than the bearing capacity of intact concrete, but are prone to brittle fracture under loading involving tension-shear interaction. GF reinforced specimens with moderate interfacial bonding exhibit better load-bearing capacity under tensile-shear stress interaction, reaching a normalized splitting peak load of 0.95 at a grouting thickness of 5 mm. PE-reinforced specimens with weak interfacial bonding provide relatively extensive energy dissipation. A 3 mm grouting layer shows favorable performance among the tested thicknesses, balancing load transfer enhancement and defect control. A single wet–dry cycle temporarily improves performance, possibly due to epoxy post-curing and pore filling, whereas repeated cycling generates cumulative micro-damage. GF- and CF-reinforced systems demonstrate the most stable resistance to short-term wet–dry conditioning. These findings provide guidance for loading-mode-dependent reinforcement selection in epoxy grouting applications. Full article

The fine powder fraction generated during concrete recycling is often regarded as a low-value by-product or used as a filler in cement-based materials. This study investigates recycled concrete powder (RCP) as the main component of pressed cement-free and low-cement mineral composites. The <0.14 mm fraction was obtained by crushing and sieving concrete waste. Cylindrical specimens were produced by semi-dry pressing at 20 MPa with a forming moisture content of 12–13% and cured under humid-air conditions. Four systems were studied: untreated RCP, thermally activated RCP, RCP with 2.5 wt.% Portland cement, and RCP with 5 wt.% Portland cement. Thermal activation was performed at 600 °C for 2 h. Compressive strength, bulk density, and water resistance coefficient were determined at 3, 7, and 28 days. At 28 days, compressive strength increased from 6.9 MPa for untreated RCP to 11.4 MPa for thermally activated RCP and 12.8 MPa for RCP with 5 wt.% cement, while the water resistance coefficient increased from 0.61 to 0.86. DTA/TGA analysis revealed thermal effects and mass-loss patterns consistent with the presence and evolution of hydrated and carbonate-containing phases. The results demonstrate that RCP can serve as a structure-forming component in pressed cement-free and low-cement materials. Full article

The Monolithic Precast Concrete Shear Wall System (MPCSWS) has become an important structural form for industrialized and sustainable construction, but its broader application is still constrained by the reliability, seismic behavior, and long-term performance of connection regions. Existing studies are abundant but remain insufficiently systematized, especially regarding the relationship among technological evolution, code-based design requirements, and engineering applicability. This review systematically examines MPCSWS connection technologies using literature retrieved from the Web of Science database and analyzed through bibliometric mapping, regulatory comparison, and engineering-oriented synthesis. Wet, dry, and hybrid connections are classified and compared in terms of load-transfer mechanisms, seismic performance, failure modes, durability concerns, and practical limitations. The review shows that wet connections remain the most mature route for achieving emulative cast-in-place behavior, whereas dry and hybrid systems provide advantages in constructability, inspectability, damage control, and potential repairability. However, unified performance evaluation criteria, durability-informed seismic assessment, and full-scale validation remain insufficient. This review provides a structured knowledge framework for MPCSWS connection technologies and discusses potential future developments in resilience-based design, intelligent monitoring, low-carbon materials, and system-level verification. Full article

Long-term dry storage is a key stage in managing spent nuclear fuel (SNF) from sodium-cooled fast reactors, for which monitoring supports aging management and future fuel-cycle decisions. This study presents a monitoring-based condition assessment of BN-350 SNF stored in 60 UKKh-123 metal–concrete casks at the dedicated long-term container storage site of the «Baikal-1» research reactor complex. The casks were transported to and placed at this site in 2010, and their condition has been monitored annually. The assessment integrates dosimetric records, full-container campaigns from 2018 and 2023, and detailed inspection data for selected packages. The monitored indicators included external gamma dose equivalent rate, surface contamination, external surface temperature, visual condition, and leak-tightness of detachable sealing connections. For all 60 packages, the maximum gamma dose equivalent rates were 5.8–25.7 μSv/h in 2018 and 2.0–20.3 μSv/h in 2023, far below the nominal 500 μSv/h value specified for normal operation by the technical operating conditions. Surface contamination remained within applicable limits, and external surface temperatures were below the nominal 84 °C operating limit. A detailed inspection confirmed low gamma dose rates and satisfactory leak-tightness. The results support continued controlled storage with periodic monitoring and safety reassessment. Full article

Coal gangue concrete (CGC) is an effective green building material that can promote the resource utilization of solid waste. To study its durability performance and degradation mechanism under sulfate attack with dry-wet cycles, and to realize the intelligent prediction of mechanical properties, this study prepared CGC specimens with a water-to-binder ratio of 0.4, a fine aggregate replacement rate of 20%, and coarse aggregate replacement rates of 0%, 20%, 50%, 80%, and 100%. The specimens were tested under 30, 60, 90, and 120 dry-wet cycles in 10% MgSO₄ solution. Mass loss, relative dynamic elastic modulus, and compressive and flexural strength corrosion resistance coefficients were used as evaluation indices, and SEM and XRD were adopted to analyze microstructural deterioration. A database compiled from literature data was established, and six machine learning models-random forest (RF), artificial neural network (ANN), decision tree (DT), support vector machine (SVM), particle swarm optimization-artificial neural network (PSO-ANN), and particle swarm optimization-support vector machine (PSO-SVM) were constructed to predict the strength corrosion resistance coefficients. Test results indicate that all macroscopic indices first increased and then decreased with the number of dry-wet cycles. Early ettringite and gypsum products filled internal pores, while prolonged sulfate attack caused decalcification and structural degradation of C-S-H gel, resulting in obvious performance loss. The PSO-SVM model showed the best prediction accuracy, with R² values of 0.912 and 0.981 for compressive and flexural strength corrosion resistance coefficients, respectively. Feature importance analysis shows that dry-wet cycles had the most significant negative impact, followed by the coal gangue fine aggregate replacement rate. This study provides support for the durability evaluation and intelligent prediction of coal gangue concrete in sulfate environments. Full article

To promote the high-value utilization of construction and demolition waste in cementitious materials, this study proposed an integrated strengthening strategy combining recycled coarse aggregate modification with cementitious matrix optimization. Recycled coarse aggregates with particle sizes of 4.75–31.5 mm were prepared from demolished concrete waste collected in Aksu, Xinjiang, China, and treated by particle shaping, alkaline solutions, and polyvinyl alcohol (PVA). Silica fume and a polycarboxylate superplasticizer were used to optimize the cementitious matrix. The physical properties of recycled aggregates, the mechanical performance of recycled aggregate concrete, and the mechanical and durability performance of high-content recycled aggregate cement-stabilized materials were evaluated. Particle shaping reduced water absorption and the crushing index from 6.8% and 14.4% to 5.6% and 12.6%, respectively. After treatment with 5% NaOH and 10% PVA, the apparent density increased to 2779 kg/m³, whereas water absorption and the crushing index decreased to 3.3% and 8.3%, meeting Class II recycled coarse aggregate requirements. With 10% silica fume and 0.2% superplasticizer, the 28-day compressive strength of recycled aggregate concrete prepared with the optimized aggregate and matrix reached 27.6 MPa, corresponding to 97.5% of that of natural aggregate concrete. The combined modification approach improved mechanical performance and reduced drying shrinkage, but the replacement ratio should be limited to 60% to satisfy the F50 freeze–thaw requirement under the tested conditions. Full article

Infrastructure construction in plateau areas not only needs to take into account the impact of harsh climatic conditions, but also faces the problem of raw material shortage. Herein, this work investigates the long-term mechanical properties, drying shrinkage, and creep behaviour of manufactured-sand concrete in plateau regions via 1-year measurements. Results show that the plateau harsh environment coarsens the pore structure of manufactured-sand concrete, leading to the 365-day compressive strength and elastic modulus dropping by at most 10.2% and 5.3%, respectively, while the 365-day drying shrinkage and specific creep increased by at most 15.3% and 9.4%, respectively. Meanwhile, with the synergistic effect of silica fume, calcium sulfate whiskers and shrinkage-reducing agent, the 365-day compressive strength increased by 12.3%, and drying shrinkage and specific creep were reduced by 10.5% and 16.6%, respectively, resulting from its dense microstructure effect. Overall, this work offers guidance for preparing high-performance concrete in plateau areas, promotes the resource utilisation of manufactured sand, and has significant implications for enhancing the service life of concrete while reducing construction costs. Full article

This study examines the post-earthquake reconstruction framework adopted in the Mt. Etna region, where the ordinances issued by the Extraordinary Commissioner provided the operational structure enabling the integration of technical, geological, and landscape-protection requirements. Geological, geophysical, and geognostic investigations were mandated to characterize local subsurface conditions and ensure that repair or reconstruction works complied with safety standards and regulatory requirements, particularly where retaining walls support buildings, roads, and infrastructure. A distinction was made between traditional dry-stone retaining walls—an essential component of the rural Etnean landscape—and reinforced concrete walls, which are adopted in contexts requiring higher structural performance. Their reconstruction involved differentiated technical approaches aimed at ensuring deformation-compatible behavior and mitigating the effects of permanent ground deformation while preserving the historical and cultural value of dry-stone constructions, recognized as UNESCO intangible heritage. The resulting reconstruction model integrates high-resolution geostructural and geophysical surveys, Active and Capable Fault (ACF) zoning criteria, and performance-based geotechnical design within a unified governance and technical protocol. This approach provides a replicable methodology for the post-seismic reconstruction of retaining walls in areas affected by permanent ground deformation and complex volcano-tectonic settings. Full article