Search Results (2,208)

The partial replacement of cement with waste-derived materials is a promising strategy for reducing cement consumption in soil–cement technologies and developing more sustainable construction materials. This study investigates fluidized bed bottom ash (BA), an industrial combustion by-product, as a partial Portland cement substitute in geotechnical cement–soil composites. Cement was replaced with BA at 5%, 10%, and 15% by mass, and specimens were tested after 3, 7, 14, and 28 days of curing. The research program combined SEM-EDS characterization, high-resolution X-ray computed tomography, uniaxial compression tests, in situ CT observations during loading, and FLAC3D mesoscale numerical modelling calibrated against experimental stress–strain curves and observed crack propagation. The results showed a non-monotonic effect of BA addition. Up to 10% BA, the median pore size remained relatively stable, whereas 15% BA increased porosity and enlarged the upper tail of the pore-size distribution. The calibrated model reproduced the global mechanical response with acceptable accuracy and captured main features of damage localization. The analyses are accompanied by a life cycle assessment (LCA). The study demonstrates that waste-modified cement–soil composites intended for sustainable soil stabilization should be evaluated not only by strength parameters, but also by internal structure, defect distribution, and environmental impact. Full article

Fiber-reinforced self-compacting concrete (FR-SCC) incorporating granite powder (GP), an expansive agent (EA), steel fibers (SFs), and polypropylene fibers (PPFs) was investigated for potential pre-cast tunnel-segment applications. Sixteen mixtures, covering GP replacement ratios of 0–18%, EA dosages of 0–8% by binder mass, and SF and PPF volume fractions of 0–0.75% and 0–0.15%, were tested in uniaxial compression on 100 mm × 100 mm × 300 mm prisms with acoustic emission (AE) monitoring. Within the tested range, 12% GP and 8% EA gave the most favorable binder composition. XRD and SEM analyses indicated that GP acted predominantly as an inert filler with no detectable portlandite consumption, while the expansive agent was associated with additional ettringite formation. At this composition, hybrid SF/PPFs increased the post-peak energy by a factor of 7.66 relative to the fiber-free mixture, mainly improving the post-peak rather than the pre-peak behavior. Among the Carreira–Chu, GB 50010, and modified Weibull formulations, the GB 50010 piecewise model best reproduced the full stress–strain curves and was used as the primary constitutive model. Two-variable regressions were established to separate the apparent effects of the SF and PPF volume fractions on the ascending- and descending-branch shape parameters, and a ductility-calibrated expression was developed for the descending-branch parameter. The Pearson coefficient between the descending-branch parameter and the AE characteristic strain was −0.904, while that between the AE characteristic strain and the macroscopic residual strain was +0.983. These results link constitutive modeling, AE damage evolution, and macroscopic post-peak ductility for FR-SCC within the tested range of mix proportions. Full article

Coal-mining-induced goaf areas are widely distributed in China and pose potential risks to high-speed railways. Repeated train-induced cyclic loading may further disturb the already weakened ground and aggravate deformation of the subgrade. A study on the goaf ground soil along the Taijiao High-Speed Railway utilized a GDS dynamic triaxial apparatus and controlled variable method to examine how waveforms, cyclic stress ratios (CSRs), effective confining pressures, vibration frequencies and cycles affect soil dynamics. The results show that cumulative plastic strain and residual pore pressure ratio generally tended to stabilize after rapid early development; however, both responses increased markedly within the 2–3 Hz frequency range. Among the investigated variables, the cyclic stress ratio (CSR) exerted the most significant influence and showed an exponential relationship with cumulative plastic strain and residual pore pressure ratio, whereas effective confining pressure produced a nearly linear decreasing trend. A dynamic stress–strain backbone curve was constructed, and by introducing the influence of vibration cycles into the H-D framework, the modified model achieved better agreement with the experimental backbone curves than the conventional H-D model. Furthermore, ABAQUS simulations further demonstrated that train speed and subgrade form significantly influence the distribution of dynamic stress and vertical displacement in goaf ground, with a more severe response in the cutting section. The optimized constitutive model and numerical results provide theoretical support for foundation design, long-term stability assessment and settlement prediction of high-speed railways constructed over goaf ground. Full article

Internal cracks during slab bending and straightening are continuous-casting defects. Existing caster curves rely on plastic deformation, while curvature variation is concentrated within short sections, causing excessive strain rates and increasing the risk of internal straightening cracks. This study proposes a novel method for slab straightening through creep deformation and develops a curve for an R9300 caster by connecting cubic transition curves with cycloidal main segments. High-temperature tensile and constant-stress creep tests of Q345C steel were combined with transient thermal simulation and geometric strain-rate calculations. Under constraints on caster height, minimum curvature radius, and steady-state creep rate, the optimized parameters were a = 2600 mm and t = 3.6 rad. The curve eliminates the circular-arc section and ensures continuous position, tangent, and curvature. Its bending and straightening sections are each 9379 mm long, increases of 8349 and 7859 mm, respectively, while caster height increases by only 0.47 m. At the internal 1200 °C isotherm, the maximum strain rates are $6.75\times {10}^{-5} {\mathrm{s}}^{-1}$ and $5.19\times {10}^{-5} {\mathrm{s}}^{-1}$, reductions of 82.2% and 81.1% relative to the conventional caster. Both remain below the steady-state creep rate of $7.45\times {10}^{-5} {\mathrm{s}}^{-1}$ under ±10% secondary-cooling and ±10 °C casting-temperature fluctuations. The curve alleviates deformation concentration and enables the slab region at 1200 °C and above to bend and straighten through creep deformation. Full article

Uniaxial compression tests were conducted on fly ash-based geopolymer concrete (FAG) with varying alkali-binder ratios (0.25, 0.35, 0.45, 0.55, 0.65) and curing ages (7 d, 28 d) to ascertain its mechanical performance parameters and stress–strain relationship curves. The formation mechanism of FAG multiscale strength is revealed through a systematic process that integrates statistical damage theory with microscopic testing techniques. This process involves the progression of microstructural state and the evolution of mesoscopic damage, providing a comprehensive understanding of the multiscale strength formation process. The results indicate that as the alkali-binder ratio increased, there was an initial rise and subsequent decline in microstructure density. At an alkali-binder ratio of 0.45, the alkaline activator can fully stimulate the fly ash to undergo depolymerization and polycondensation reactions. The result of this process is the formation of a continuous and dense cementitious matrix, thereby achieving the optimal improvement in macroscopic initial mechanical properties. Concurrent microstructural alterations further modify the morphology and path of microcrack initiation and propagation during uniaxial compression, as well as the effective force skeleton adjustment process. The characteristic parameters that are indicative of the evolution of microfracture and yield damage demonstrate regular changes in accordance with the alkali-binder ratio. The joint effect of these two factors determines the evolution characteristics of the macroscopic nonlinear stress–strain behavior of FAG, ultimately resulting in an increasing and then decreasing trend of FAG strength with the increase of alkali-binder ratio, while ductility shows a trend of decreasing first and then increasing. At an equivalent alkali-binder ratio, the porosity of the 7 d sample exhibited a decrease of 1.13% to 17.13%. Conversely, the strength of the 7 d sample increased by 39% to 312%. However, the deformation capacity of the 7 d sample decreased, with a peak strain reduction of 21% to 52% at 28 d. This research achievement has the potential to provide significant theoretical support for the practical engineering promotion and application of FAG. Full article

Lunar regolith simulant (LRS) geopolymers are promising construction materials for lunar in situ resource utilization, but their brittle behavior and limited crack resistance restrict their structural applications. This study investigated the effect of basalt fiber length on the mechanical properties, failure modes, stress–strain behavior, constitutive relationship, and microstructure of CQU-1 LRS geopolymers. Basalt fiber-reinforced LRS geopolymers were prepared under weak alkali activation and high-temperature curing at 80 °C. The basalt fiber content was fixed at 0.1%, and six fiber lengths of 0, 6, 9, 12, 15, and 18 mm were considered. Compressive and flexural tests were conducted after curing for 1 d and 7 d, and the normalized stress–strain curves were fitted using the Saenz L.P., Carreira D.J., and Zhenhai Guo models. The results showed that basalt fiber length significantly affected the mechanical performance of LRS geopolymers. An appropriate fiber length improved strength, stiffness, ductility, and post-peak load-bearing capacity, whereas excessively short or long fibers weakened the reinforcing effect. The 15 mm fiber group exhibited the best overall performance. After curing for 1 d, its compressive strength reached 2.23 MPa, 49.7% higher than that of the control group, and its elastic modulus increased approximately 2.5-fold. After curing for 7 d, its compressive strength reached 13.44 MPa, 32.0% higher than that of the control group. The Zhenhai Guo model provided the best fit for the stress–strain curves. SEM-EDS analysis showed that basalt fibers improved interfacial bonding and promoted gel enrichment near the fiber–matrix interface. Overall, 15 mm was recommended as the optimal basalt fiber length for CQU-1 LRS geopolymers under the conditions used in this study. Full article

Large-scale thick curved components made of high-strength steel are critical to deep-sea pressure hulls and large structural components of engineering machinery. During forming, these components experience reverse loading upon unloading, and the pronounced Bauschinger effect of high-strength steel significantly compromises springback prediction accuracy, leading to costly die iterations. Existing cyclic tension–compression and shear tests are limited to uniaxial stress states and fail to capture the mechanical behavior under in-plane biaxial cyclic loading. Herein, a cyclic four-point bending method is proposed to characterize the Bauschinger effect of Q890 steel under biaxial cyclic loading. By tailoring the width-to-thickness ratio of the specimens, a series of plane stress states with different initial plastic stress ratios were obtained, covering the dominant stress conditions encountered in forming typical large-scale double-curvature thick plates. Full-field strain evolution during cyclic bending was captured in real time via digital image correlation (DIC), enabling systematic acquisition of equivalent stress–strain curves under various biaxial stress ratios over multiple cycles. As the width-to-thickness ratio increases, both forward and reverse yielding progressively degrade: the equivalent yield strength, forward peak flow stress, and reverse yield strength drop from 1098, 1193, and 742 MPa to 934, 1065, and 685 MPa, respectively. Accordingly, the Bauschinger ratio B, Bauschinger hardening parameter BHP, and Bauschinger energy parameter BEP decrease from 0.479, 0.789, and 4.747 to 0.363, 0.655, and 2.900, respectively, revealing a strong stress-ratio dependence of the Bauschinger effect. Notably, the springback ratio also shows clear dependence on the biaxial stress ratio, loading direction, and cyclic history, indicating that in-plane biaxial stress-state effects should be considered when characterizing the Bauschinger effect and springback behavior of Q890 high-strength steel. Full article

This paper presents a modified version of the Booker et al. cycle-based pore pressure generation model for use with strain-controlled cyclic loading tests on sandy soils. The original Booker et al. model has been widely used in geotechnical engineering because of its simplicity and computational efficiency; however, it was developed using stress-controlled cyclic test data and does not accurately capture the pore pressure response observed in strain-controlled cyclic loading. In strain-controlled tests, excess pore pressure typically develops rapidly during the early stages of loading and more gradually as liquefaction is approached, resulting in a pore pressure–cycle ratio relationship fundamentally different from that produced by the original model. To address this limitation, a Modified Booker Model was developed through curve fitting of laboratory test data obtained from strain-controlled cyclic triaxial and cyclic direct simple shear tests. The model was evaluated using the results of 51 cyclic triaxial tests and 101 cyclic direct simple shear tests performed on clean sands and sand–silt mixtures with fines contents both above and below the threshold fines content (TFC). The model produced excellent agreement with measured pore pressure responses, yielding average coefficients of determination (R²) ranging from 0.921 to 0.989 depending on the test type and soil conditions. The results indicate that the Modified Booker Model provides a practical, accurate, and computationally efficient method for predicting pore pressure generation during strain-controlled cyclic loading of sands and silty sands. Full article

Shear modulus degradation curves are fundamental inputs in nonlinear site response analyses and are conventionally normalized by the small-strain shear modulus, G_max, defined at shear strains on the order of γ ≈ 10⁻⁴%. In shaking table experiments, however, reliable measurements at very small strains are often unattainable due to instrumentation resolution and strain demand limitations. Consequently, normalization is frequently performed using the shear modulus at a higher reference strain (γ = 0.01%). The impact of this alternative normalization on the resulting shear modulus degradation relationship has not been systematically evaluated. This study investigates the influence of normalization strain level on shear modulus degradation behavior using stress–strain relationships reconstructed from shaking table acceleration records. The shear modulus values were computed from individual hysteresis loops. The shear modulus normalized by G_max estimated from empirical correlations was compared with the shear modulus normalized by its value at γ = 0.01% directly obtained from shaking table measurements. Results indicate that normalization at γ = 0.01% produces slightly lower normalized modulus values for shear strains exceeding 0.01% compared with the curve normalized by G_max. Normalization using G_γ=0.01% resulted in reduced scatter and uncertainty. Full article

Alkali-activated slag–loess cemented backfill materials are subjected to coupled confining pressure and curing temperature in open-pit end-slope backfill mining. This study investigates their mechanical properties and microscopic mechanisms under four confining pressures (0, 2, 4, and 6 MPa) and four curing temperatures (5, 20, 35, and 50 °C) at a curing age of 7 days. Uniaxial and triaxial compression tests were conducted to obtain stress–strain curves, peak strength, elastic modulus, cohesion, and internal friction angle. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an improved simulated annealing algorithm for three-dimensional pore reconstruction were used to characterize pore diameter, porosity, connectivity, and hydration products (calcium-silicate-hydrate (C-S-H), calcium-aluminosilicate-hydrate (C-A-S-H), and sodium-aluminosilicate-hydrate (N-A-S-H)). The results show that increasing confining pressure flattens the post-peak softening curve and transitions failure from brittle to ductile, while rising curing temperature shortens the compaction stage and increases elastic modulus. Both factors increase peak strength synergistically. Cohesion increases nonlinearly with temperature (2.64 MPa at 5 °C to 6.27 MPa at 50 °C), whereas the internal friction angle (13°) is temperature-insensitive. Microscopically, confining pressure reduces pore diameter, porosity, and connectivity via physical compaction; curing temperature promotes gel production, decreasing porosity from 26.23% to 13.95% and connectivity from 64.87% to 34.89%. This study provides a theoretical basis for backfill design and ground pressure management in open-pit end-slope mining. Full article

Background: Currently, there is a lack of biomechanical studies on traditional dual-growing rods (TDGR) combined with apical osteotomy and short-segment fusion (hybrid technique, HT). This study compared the differences in clinical outcomes and biomechanics between TDGR and HT in the treatment of severe early-onset scoliosis (sEOS) via finite element analysis (FEA) and in vitro biomechanical experiments. Methods: Two scoliotic FEA models and 12 in vitro scoliotic models were created. In the FEA, the initial surgeries for TDGR and HT, two subsequent lengthenings, and up to 12 months of physeal spinal growth were simulated. In the in vitro biomechanical experiments, the initial surgeries were simulated. Correction outcomes, spinal height, and stress were compared between the TDGR and HT groups. Results: (1) FEA: Compared with TDGR, HT achieved better correction (62.4% vs. 36.2%) and a greater increase in spinal height (26.43 mm vs. 12.58 mm) after the initial surgery. During follow-up, HT resulted in better correction maintenance and could better sustain spinal growth than TDGR. HT reduced the stress on the proximal and distal instrumented vertebral bodies, junctional intervertebral discs, and instrumentation compared with TDGR. (2) In vitro biomechanical experiment: After the initial surgery, the mean Cobb angle of the main curve (24.58 ± 2.80° vs. 38.97 ± 3.23°) and AVT (8.87 ± 1.64 mm vs. 13.15 ± 3.58 mm) in the HT group were significantly lower than those in the TDGR group (p < 0.05). The increase in spinal height in the HT group was significantly greater than that in the TDGR group (3.83 ± 0.45 cm vs. 1.85 ± 0.72 cm, p < 0.001). Compared with TDGR, HT significantly decreased rod strain (p < 0.05). Conclusions: Compared with TDGR, HT can significantly improve correction outcomes and maintain spinal growth. Apical anchors can effectively disperse stress on the spine and instrumentation, which may reduce the risk of complications and potentially delay intervertebral disc degeneration, although clinical validation is required. Full article

This study investigates the mechanical properties and uniaxial compression behavior of nano-TiO₂-modified coral concrete (NTCC). Twelve groups of specimens with different nano-TiO₂ contents were prepared and cured in freshwater, seawater, and oxalic acid environments. Cube compressive strength, splitting tensile strength, and uniaxial compression tests were conducted according to relevant standards. The results indicate that nano-TiO₂ significantly enhances the mechanical performance of coral concrete. The compressive and tensile strengths initially increased and then decreased with increasing nano-TiO₂ content, with the maximum strength improvement reaching approximately 22%. Furthermore, increasing the nano-TiO₂ dosage reduced the brittle failure characteristics of NTCC under compression. The curing environment had a significant influence on the performance of NTCC. Specimens cured in seawater exhibited superior early-age strength, whereas those cured in freshwater achieved the highest later-age strength. The stress–strain response of NTCC under uniaxial compression can be divided into three stages: the elastic stage, elastoplastic stage, and descending stage. Based on the experimental results, an empirical constitutive model was proposed for NTCC. The predicted stress–strain curves showed good agreement with the experimental results, demonstrating the applicability of the proposed model for describing the compressive behavior of NTCC. Full article

Residual stress in brittle films on compliant substrates is routinely inferred from fragmentation experiments by combining an elastic stress-transfer model with a fracture strength criterion. This inversion is inherently coupled because the observed crack spacing depends jointly on the residual stress and the film fracture strength. Conventional closed-form estimators typically rely on a single feature, such as the cracking onset strain, and prescribe the fracture strength a priori, often at its bulk value. This practice discards most of the information encoded in the full crack-spacing evolution. It also obscures two sources of uncertainty: the intrinsic variability of thin-film fracture strength and the limited sensitivity of any single observable to individual parameters. Here, we recast the inversion as a Bayesian physics-informed neural network (B-PINN) in which the entire measured curve of the mean crack spacing versus applied strain is likely to occur. Stochastic gradient Langevin dynamics then sample the joint posterior of residual stress and fracture strength. A central finding is that crack-spacing data alone constrain only the difference between fracture strength and residual stress, confining the posterior to a one-dimensional manifold in parameter space and leaving each quantity individually unresolved. A single substrate curvature measurement, which, through the Stoney relation, depends on the residual stress but not on the fracture strength, provides the missing orthogonal constraint and collapses the posterior to a tight, well-resolved region. We further derive an identifiability condition under which buckle-wavelength observations serve as a third independent channel for recovering interface adhesion energy, and provide a synthetic proof-of-concept of this three-channel extension on DLC/Si and Mo/Si datasets; an experimental validation of the adhesion channel is identified as the natural next step but lies beyond the present scope. Requiring only standard fragmentation measurements and a single non-destructive curvature scan, the framework converts a point-estimate procedure into a posterior-quantified inverse method that makes explicit what can, and cannot, be learned from thin-film mechanics experiments. Full article

With the advancement of marine engineering, coral concrete—comprising coral coarse aggregate, coral sand, and seawater—has garnered increasing research interest. To further investigate its compressive mechanical behavior under axial and lateral biaxial stress states, a total of 9 prismatic specimens under axial loading and 45 cubic specimens under biaxial loading were prepared, encompassing three strength grades (C20, C30, and C40) and five lateral stress ratios (0, 0.25, 0.5, 0.75, and 0.9). The failure modes and corresponding axial and biaxial stress–strain curves were meticulously recorded. The axial mechanical response was systematically analyzed, leading to the establishment of a compressive damage constitutive model based on the Weibull distribution. Additionally, the influence of the lateral stress ratio on both peak stress and peak strain was examined, and multiple biaxial failure criteria were formulated. Experimental results reveal that the failure modes of coral concrete specimens are analogous to those of natural coarse aggregate concrete and are significantly affected by the lateral stress ratio. Specifically, an increase in the lateral stress ratio results in higher peak stress, while the absolute value of peak strain exhibits a linear variation. Finally, the proposed axial damage constitutive model and the biaxial failure criteria are rigorously validated against the experimental data. Full article

Foamed concrete has been used to construct lightweight embankments as a substitute for conventional fills, aiming to promote its engineering application in soft-soil regions. However, the dynamic response and safety mechanism of foamed concrete embankments during vehicle collision are not yet fully understood. In this paper, the safety performance of lightweight foamed concrete embankments under vehicle–guardrail collision and the optimal design of the guardrail foundation are investigated from the perspectives of lateral displacement and stress distribution. Through static uniaxial compression tests, the stress–strain curves, compressive strength, elastic modulus, and statistical variability of foamed concrete with six different mix proportions were obtained. On this basis, a coupled finite element model of the vehicle–guardrail–lightweight embankment system was established (the guardrail and its foundation were modeled using a linear elastic constitutive model, the embankment using a crushable foam model, and the vehicle using a 1.5 t passenger car model validated by full-scale crash tests). According to the passenger car impact conditions specified in current Chinese regulations (velocity 100 km/h, angle 20°), the peak lateral displacement and peak principal stress of the lightweight embankment were analyzed for four foundation base slab lengths (L₀, 1.1 L₀, 1.2 L₀, 1.3 L₀). The results show that increasing the base slab length effectively reduces lateral displacement and stress concentration. Increasing the length by 10–20% reduces the peak lateral displacement by up to 68%, and the peak principal stress remains far below the material strength. From the perspectives of structural stability and cost-effectiveness, a 10–20% increase in the base slab length is recommended. The ratio of the peak principal stress to the material strength can serve as a criterion for evaluating the safety margin and assessing the rationality of the foundation design. This study provides quantitative evidence for optimizing the guardrail foundation base slab length to enhance the collision safety of lightweight foamed concrete embankments, and the proposed design range offers a cost-effective reference for practical engineering applications in soft-soil regions. Full article