Search Results (114)

Expansive soil is prone to significant swelling and shrinkage deformation with changes in moisture conditions, posing serious safety hazards to engineering construction. This study focuses on alkali-activated self-compacting fluid-solidified soil (ASFS) and systematically explores the regulatory effect of expansive soil with different dosages (0–100%) on its properties. This study analyzes the influence of expansive soil on the setting time, hydration characteristics, autogenous shrinkage, and compressive strength of ASFS while verifying the feasibility of this method for solidifying expansive soil through microstructural analysis. The results show that, with the increase in content of expansive soil, the initial and final setting times of ASFS were prolonged by 0.08–1.58 times and 0.08–1.29 times, respectively. Although expansive soil inhibited the hydration of ASFS, it could compensate for autogenous shrinkage through the expansion effect of clay minerals, reducing the autogenous shrinkage by 13.4–51.2%. Furthermore, the optimal dosage of expansive soil in ASFS is 60%. Compared with the control group, the 7d compressive strength of ASFS increases by 52.4%, the strength after 3d water immersion rises by 62.6%, and the strength after eight wet–dry cycles still remains 10% higher. This optimal dosage achieves the best balance between mechanical properties, water stability, and shrinkage resistance of ASFS, providing a reliable technical reference for the efficient utilization of expansive soil in engineering. Full article

The bonding interface between repair materials and concrete substrate is the weakest link in the entire repair structure. If the interface bonding performance is insufficient, the repair material is prone to cracking or falling off, leading to repair failure. The shrinkage of repair materials is one of the primary factors affecting the bonding performance of these interfaces. In this study, sulphoaluminate cement (SAC) was used to improve the repair performance of ordinary Portland cement (OPC)–granulated blast furnace slag (GGBS) composite repair materials. The influence of SAC on the mechanical properties, bonding performance, expansion behavior, impermeability, and hydration heat of OPC-GGBS-SAC composite repair materials was investigated. The results demonstrate that the rapid hydration of SAC significantly improved the early strength and mechanical properties of the composite system at negative temperatures. The hydration products filled the pores within the concrete matrix, thereby enhancing the mechanical meshing effect at the interface. The early expansion effect of SAC formed a pre-stressor at the interface, which not only strengthened the bonding force between repair materials and the substrate, but also effectively inhibited the shrinkage of the composite system and prevented crack formation, thus significantly promoting the long-term reliability of the bonding interface. An appropriate amount of SAC can accelerate the hydration process of OPC-GGBS system, advance the exothermic peak, and promote the development of early strength. However, excessive incorporation will inhibit the later hydration of the composite system due to the way in which the hydration products wrap the cement particles. When the content of SAC was 5–10%, optimal comprehensive properties of the OPC-GGBS-SAC composite system were attained. Full article

Metal binder jetting (MBJ) is an additive manufacturing technology of increasing interest due to its potential competitiveness in medium- and large-scale production, especially from a sustainability perspective. However, challenges in controlling the product accuracy and precision significantly limit the widespread adoption of this technology. This work investigates the achievable accuracy, precision, and spatial repeatability of parts produced using the MBJ process. Additionally, the paper aims to identify the causes of inaccuracy and suggest countermeasures to improve the product quality. The study was conducted experimentally by designing a benchmark geometry with various basic features. This geometry was scaled to three sizes—10–20 mm (small), 20–30 mm (intermediate), and 30–50 mm (large)—and produced using two different stainless-steel powders: AISI 316L and 17-4PH. In the green state, the dimensional tolerances ranged from IT8 to IT12 for features parallel to the build direction (heights) and from IT9 to IT13 for features parallel to the build plane (lengths). In the sintered state, the tolerances ranged from IT10 to IT16. This study reveals the challenges in scaling geometries to compensate for accuracy loss originating from the printing and sintering stages. In the green state, accuracy issues are likely due to non-uniform binder application and drying operations. In the sintered state, the accuracy loss is related to variable shrinkage based on the feature size, anisotropic shrinkage depending on the print direction, and differing densification mechanisms influenced by the material type. This study offers novel insights for improving MBJ process precision, supporting wider adoption in the manufacturing industry. Full article

The method addresses the challenges of non-steady conditions at an early age by combining wavelet filtering and empirical mode decomposition (EMD) to separate strain components arising from shrinkage, expansive agent compensation, temperature variations, construction disturbances, and live loads. The approach incorporates construction logs as external constraints to ensure accurate correspondence between signal features and physical events. Scientifically, this study addresses the fundamental problem of identifying and quantifying multi-source strain components under transient and non-steady construction conditions, which remains a major challenge in the field of structural monitoring. Field monitoring was conducted on typical cast-in-place concrete components: a full-width bridge deck in the negative moment region. The results show that both structural types exhibit a distinct shrinkage–recovery process at an early age but differ in amplitude distribution, recovery rate, and restraint characteristics. During the construction procedure stage, the cast-in-place segment in the negative moment region was sensitive to prestressing and adjacent segment construction. Under variable loads, the former showed higher live load sensitivity, while the latter exhibited more pronounced temperature-driven responses. Total strain decomposition revealed that temperature and dead load were the primary long-term components in the structure, with differing proportional contributions. Representative strain variations observed in the field ranged from 10 to 50 µε during early-age shrinkage–expansion cycles to 80–100 µε reductions during prestressing operations, quantitatively illustrating the evolution characteristics captured by the proposed method. This approach demonstrates the method’s capability to reveal transient stress mechanisms that conventional steady-state analyses cannot capture, providing a reliable basis for strain monitoring, disturbance identification, and performance evaluation during construction, as well as for long-term prediction and optimization of operation–maintenance strategies. Full article

The synergy between carbon neutrality and urbanization is essential for effective climate governance and socio-ecological intelligent transition. From the perspective of coupled urban dynamic evolution and carbon metabolism systems, this study integrates the Sen-MK trend test and the geographical detector model to explore the spatial–temporal differentiation patterns and driving mechanisms of carbon balance across 337 prefecture-level cities in China from 2012 to 2022. The results reveal a spatial–temporal mismatch between carbon emissions and carbon storage, forming an asymmetric carbon metabolism pattern characterized by “expansion-dominated and shrinkage-dissipative” dynamics. Carbon compensation rates exhibit a west–high to east–low gradient distribution, with hotspots of expansionary cities clustered in the southwest, while shrinking cities display a dispersed pattern from the northwest to the northeast. Based on the four-quadrant carbon balance classification, expansionary cities are mainly located in the “high economic–low ecological” quadrant, whereas shrinking cities concentrate in the “low economic–high ecological” quadrant. Industrial structure and population scale serve as the dual-core drivers of carbon compensation. Expansionary cities are positively regulated by urbanization rates, while shrinking cities are negatively constrained by energy intensity. These findings suggest that differentiated regulation strategies can help optimize carbon governance within national territorial space. Full article

Mineral expansive from FDG—flue-gas desulfurization—blended with calcium aluminate cement CAC was analyzed as mitigation shrinkage of alkali-activated residual mortars AAM. The AAM mortars were composed of red mud (RM) and bottom ash (BA), as precursors of a metakaolin MK-based system. MK replacement (0, 50, 70%) in alkaline solution (10M) and ratio 1:2 (binder/sand) was studied. Engineering properties were performed, and included mechanical strength, setting times, and dry shrinkage (HR 60%), as well as the microstructure formed at 7 d and 28 days. A total of 10% CAC-FGD dosage was the most efficient, reducing drying shrinkage by 23% and autogenous shrinkage by up to 30%. The findings showed that this addition also improved mechanical strength by approximately 16% at 28 days. Under the addition of CAC-FGD, the results suggest the presence of aluminosilicate gels of the (Na,C)-(A)-S-H type and the formation of ettringite, which are possibly responsible for ensuring good performance and a controlled expansion that, in turn, compensates for the shrinkage of the activated mortars. Full article

Achieving high dimensional accuracy in the build direction remains a critical challenge in laser-based powder bed fusion of metals (PBF-LB/M), particularly for taller components. This study investigates the application of the standardized Z-artefact defined in ISO/ASTM 52902:2023 to evaluate and correct vertical dimensional deviations in AlSi10Mg parts. Benchmark artefacts were produced without Z-scaling and measured using a structured light 3D scanner. A linear trend of increasing undersizing with build height was observed across two build jobs, indicating a systematic Z-error. Based on the reproducible average deviation, a shrinkage compensation factor of 1.0017 was derived and applied in a third build job using the same processing parameters. This correction reduced the root mean square error (RMSE) from over 100 µm to below 25 µm and improved the achievable ISO tolerance grades from IT 9–11 to IT 5–9. The approach proved effective without requiring changes to process parameters. However, local surface features such as elevated edges and roughness remained dominant sources of deviation and are not captured in step height-based evaluations. Overall, this study demonstrates a practical, standard-compliant method to improve vertical dimensional accuracy in PBF-LB/M, with potential applicability to industrial quality assurance and future extension to more complex geometries. Full article

Heat-curing processes are often used to ensure the production rate of precast concrete elements, as this process increases the early strength of the material. However, the increase in curing temperature can negatively affect the final mechanical properties since cracking, and especially high porosity, may occur under these conditions. In order to compensate for the expected loss in mechanical and durability-related properties, the cement content is typically increased. This solution raises the cost of the final product and reduces its sustainability. Thus, in this study, the development of expansive self-compacting concretes (SCCs) is proposed to achieve higher final mechanical properties without increasing cement contents. The mechanical properties, expansive performance, and porous microstructure have been evaluated under different curing regimes. The obtained results show that it is possible to obtain similar or even better mechanical performance in expansive concretes cured at high temperatures than in those cured in standard conditions, particularly when using ettringite-based expansive agents (EAs). Moreover, the use of limestone filler (LF) proved to be more suitable than the use of fly ashes in the working conditions evaluated in the present study. In this sense, the compressive strength at 28 days of SCC with LF and ettringite-based EAs is 4.3% higher than the one obtained under standard curing; moreover, the total porosity is reduced (5%), and the drying shrinkage is also limited. These aspects have not been previously reported in non-expansive heat-cured concretes and represent a unique opportunity to reduce the cement content and, therefore, the carbon footprint of precast concretes without reducing their mechanical properties. When using CaO-based EAs, the results are also better than those of non-expansive SCC, although the improvement is less pronounced than in the previous case. Full article

Cracking is the most prevalent deterioration issue in historic masonry, and grouting represents one of the most effective intervention techniques. Superplasticizer-free Natural Hydraulic Lime (NHL) grout is recommended for heritage conservation due to its simple composition and compatibility with historic masonry in terms of strength, porosity, and other properties. However, grout shrinkage is frequently observed in practice, often leading to suboptimal reinforcement outcomes. This study focuses on the shrinkage characteristics of NHL grouts. Three sets of experiments were designed to investigate the influence: grout composition, expansive agents, and substrate properties. Using Taguchi’s method, an optimized combination of water, binder, and aggregate was identified. Shrinkage measurements after curing for 28 days demonstrated that calcium oxide (CaO)-based expansive agents was the best choice to compensate for NHL grout shrinkage. In addition, grouting simulation experiments evaluated suitable formulations for common masonry substrates and clarified the significant impact of substrate water absorption on the degree of shrinkage grout. For substrates with a capillary water absorption coefficient greater than 25 kg/m² h^1/2, the use of expansive agents should be strictly controlled. The findings can provide valuable insights for optimizing the grouting reinforcement of historic masonry structures and offer direct material design strategies for practical engineering applications. Full article

Over recent decades, coastal wetlands in Jiangsu Province have faced multiple challenges, including overfishing, reclamation for aquaculture, wetland shrinkage, and biodiversity loss. Implementing wetland ecological restoration proves crucial for mitigating the degradation of coastal wetland ecosystems. Quantifying ecosystem service values and establishing rational ecological compensation standards provide essential references for ecological compensation research and alleviating human–land conflicts. The Jianchuan Ecological Restoration Project, located in Dafeng District of Yancheng City, Jiangsu Province, employs integrated wetland, woodland, and farmland construction to rebuild biodiversity, enhance water conservation capacity, and improve water purification functions, thereby significantly boosting regional ecological services. Results have demonstrated that the total ecosystem service value of this project reaches CNY 76.2896 million, with climate regulation representing the highest value (CNY 68.1496 million, 89.33% of total). Subsequent values include biodiversity maintenance (3.40%), water purification (3.31%), and food production (2.95%), while carbon sequestration/oxygen release (0.96%) and soil retention (0.05%) show relatively lower contributions. Notably, this project innovatively integrates carbon finance mechanisms through “carbon sink loans”, achieving efficient transformation of ecological value from “paper accounts” to market realization. This study establishes a scientific foundation for ecological restoration projects through ecosystem service-based value assessment and pathway exploration, offering both theoretical framework and practical references. Full article

Rapid pavement repair demands materials that combine accelerated strength gains, dimensional stability, long-term durability, and sustainability. However, finding materials or formulations that offer these balances remains a critical challenge. This study systematically evaluates two polymer-modified belitic calcium sulfoaluminate (CSA) concretes—CSAP (powdered polymer) and CSA-LLP (liquid polymer admixture)—against a traditional Type III Portland cement (OPC) control under both laboratory and realistic outdoor conditions. Laboratory specimens were tested for fresh properties, early-age and later-age compressive, flexural, and splitting tensile strengths, as well as drying shrinkage according to ASTM standards. Outdoor 5 × 4 × 12-inch slabs mimicking typical jointed plain concrete panels (JPCPs), instrumented with vibrating wire strain gauges and thermocouples, recorded the strain and temperature at 5 min intervals over 16 weeks, with 24 h wet-burlap curing to replicate field practices. Laboratory findings show that CSA mixes exceeded 3200 psi of compressive strength at 4 h, but cold outdoor casting (~48 °F) delayed the early-age strength development. The CSA-LLP exhibited the lowest drying shrinkage (0.036% at 16 weeks), and outdoor CSA slabs captured the initial ettringite-driven expansion, resulting in a net expansion (+200 µε) rather than contraction. Approximately 80% of the total strain evolved within the first 48 h, driven by autogenous and plastic effects. CSA mixes generated lower peak internal temperatures and reduced thermal strain amplitudes compared to the OPC, improving dimensional stability and mitigating restraint-induced cracking. These results underscore the necessity of field validation for shrinkage compensation mechanisms and highlight the critical roles of the polymer type and curing protocol in optimizing CSA-based repairs for durable, low-carbon pavement rehabilitation. Full article

To address the poor thermal shock resistance and high brittleness of traditional ceramic tools, a novel Si₃N₄/Sc₂W₃O₁₂ (SNS) composite ceramic material was developed via in situ synthesis using WO₃ and Sc₂O₃ as precursors and consolidated by spark plasma sintering. Sc₂W₃O₁₂ with negative thermal expansion was introduced to compensate for matrix shrinkage and modulate interfacial stress. The effects of varying Sc₂W₃O₁₂ content on thermal expansion, residual stress, microstructure, and mechanical properties were systematically investigated. Among the compositions, SNS3 (12 wt.% Sc₂W₃O₁₂) exhibited the best overall performance: relative density of 98.8 ± 0.2%, flexural strength of 712.4 ± 30 MPa, fracture toughness of 7.5 ± 0.3 MPa·m^1/2, Vickers hardness of 16.3 ± 0.3 GPa, and an average thermal expansion coefficient of 2.81 × 10⁻⁶·K⁻¹. The formation of a spherical chain-like Sc-W-O phase at the grain boundaries created a “hard core–soft shell” interface that enhanced crack resistance and stress buffering. Cutting tests showed that the SNS3 tool reduced workpiece surface roughness by 32.91% and achieved a cutting distance of 9500 m. These results validate the potential of this novel multiphase ceramic system as a promising candidate for high-performance and thermally stable ceramic cutting tools. Full article

The constitutive model significantly influences the accuracy of predicting the complex rheological behavior of hot isostatically pressed powders. The temperature plays a crucial role in determining material properties during hot isostatic pressing (HIP), making it essential to account for its effect on the yield model parameters to more accurately describe the densification evolution of powders. In this study, HIP experiments were conducted using two different process schemes, and the shrinkage deformation of the envelope under each scheme was analyzed. High-temperature uniaxial compression experiments were performed on HIP samples with varying densities to analyze and characterize the stress–strain response of the powder during HIP. A mesoscopic particle-scale high-temperature uniaxial compression model was developed based on the discrete element method (DEM), and the strain and stress values corresponding to different densities in the high-temperature uniaxial compression simulations were validated through experimental comparison. The strain evolution during the uniaxial compression process was analyzed, and the relationship between the parameters of the Shima–Oyane model and the temperature was established, leading to the development of a temperature-compensated Shima–Oyane model. Based on the obtained parameters at various densities and temperatures, a yield stress map for the nickel-based alloy was constructed. The accuracy of this model was verified by comparing experimental results with finite element method (FEM) simulations. The findings of this study contribute to a more precise prediction of densification behavior in thermally driven isostatic pressing. Full article

The article presents a three-stage methodology for calibrating 3D printing using mSLA technology, aimed at improving dimensional accuracy and print repeatability. The proposed approach is based on procedures that enable the collection and analysis of numerical data, thereby minimizing the influence of the operator’s subjective judgment, which is commonly relied upon in traditional calibration methods. In the first stage, compensation for the uneven illumination of the LCD matrix was performed by establishing a regression model that describes the relationship between UV radiation intensity and pixel brightness. Based on this model, a grayscale correction mask was developed. The second stage focused on determining the optimal exposure time, based on its effect on dimensional accuracy, detail reproduction, and model strength. The optimal exposure time is defined as the duration that provides the highest possible mechanical strength without significant loss of detail due to the light bleed phenomenon (i.e., diffusion of UV radiation beyond the mask edge). In the third stage, scale correction was applied to compensate for shrinkage and geometric distortions, further reducing the impact of light bleed on the dimensional fidelity of printed components. The proposed methodology was validated using an Anycubic Photon M3 Premium printer with Anycubic ABS-Like Resin Pro 2.0. Compensating for light intensity variation reduced the original standard deviation from 0.26 to 0.17 mW/cm², corresponding to a decrease of more than one third. The methodology reduced surface displacement due to shrinkage from 0.044% to 0.003%, and the residual internal dimensional error from 0.159 mm to 0.017 mm (a 72% reduction). Full article

Three-dimensional printing is rapidly growing in applied dentistry. In order to print faster, increase workflow, and minimize the consumption of resin material, it is important to use the right printer and the correct printing orientation. The objective of the present report is to analyze the flexural strength of specimens realized with two different dental light-curing resins (Keyguide and C&B) obtained from two different Digital Light Processing (DLP) 3D printers. Different printing orientations (0°, 45°, and 90°) were evaluated. 3D Builder, MeshMixer, RayWare, and Chitubox software were used to design the resin specimens. A total of 15 Keyguide and 15 C&B specimens in the shape of a rectangular parallelepiped, with dimensions of 2 mm × 2 mm × 25 mm, were obtained with the Sprintray Moonray S 3D printer, and the 15 Keyguide and 15 C&B specimens presented the same characteristics as those printed using the Moon Night printer. Prior to sample printing, a calibration protocol (tolerance test and dimensional accuracy test) was performed using RayWare software. This procedure allowed compensation for resin shrinkage or expansion, thus ensuring dimensional consistency in all printed samples. Each resin specimen, after printing and post-processing (MoonWash 2 and MoonLight 2), was subjected to a mechanical test with a universal testing machine. After breaking the specimen, the flexural strength values were recorded with computer software (Bluehill, Instron Corporation, Canton, MA, USA). According to the results obtained, the printing orientation of the specimens does not affect the flexural strength of the two materials examined. However, at the maximum load, some differences emerged for both materials printed with the Moon Night printer, depending on their build angle. Both light-cured resins tested had a higher maximum load resistance when printed with the newer Moon Night printer. This result could be due to the Moon Night printer’s better construction characteristics compared to those of the Sprintray or to issues related to the dimensional calibration of the specimens. Full article