Search Results (2,457)

Air void content (Va) is a key volumetric parameter governing the performance of Stone Mastic Asphalt (SMA), yet its prediction becomes challenging when steel slag, fibers, and additives are incorporated. This study develops an interpretable machine learning framework for predicting Va using 74 mixtures collected from 16 published studies and nine mixture-related variables. XGBoost was optimized using Particle Swarm Optimization and Grey Wolf Optimizer (GWO), with the best configuration obtained by GWO at a population size of 40 and a minimum development-stage 5-fold cross-validation (CV) RMSE of 0.371%. On the principal 70/30 evaluation partition, the optimized model achieved R² = 0.944, RMSE = 0.397%, MAE = 0.262%, and MAPE = 0.054, outperforming the evaluated benchmark models in R², RMSE, MAE, and MAPE. Robustness analyses showed that prediction accuracy was sensitive to data partitioning and literature-source composition, indicating that the reported performance should be interpreted within the represented data domain. SHAP, permutation importance, and feature-ablation analyses consistently identified binder penetration as the most influential predictor, followed mainly by asphalt content and softening point. Overall, the proposed framework provides an interpretable tool for preliminary Va estimation and mixture screening, while independent laboratory and field validation remains necessary before practical deployment. Full article

Ultra-high-performance concrete (UHPC) is characterized by exceptional compressive strength; however, its structural performance is primarily governed by tensile behavior, fracture resistance, and energy dissipation. This study presents a comprehensive mechanical characterization of a steel fiber-reinforced UHPC incorporating a slag–limestone powder-based binder system with a low water-to-binder ratio of 0.15 and steam curing at 90 °C for 48 h. The experimental program comprised compressive strength, flexural behavior, split and direct tensile response, impact energy absorption, ultrasonic pulse velocity, and an assessment of specimen size and geometry effects. The UHPC achieved mean compressive strengths of approximately 209 and 218 MPa at 7 and 28 days, respectively, in 75 × 150 mm cylindrical specimens, indicating only modest strength development after the initial steam-curing period. Smaller cube specimens exhibited higher nominal compressive strengths, reaching approximately 221 and 227 MPa at 7 and 28 days, respectively, demonstrating a measurable but limited specimen-size effect. Flexural testing produced an average strength of 33.1 MPa and a stable post-peak response, although no strain hardening in bending was observed. Split tensile strength reached approximately 16.1 MPa, exceeding that of conventional normal-strength concrete by more than four times. Direct tensile tests demonstrated an intrinsically ductile response, with tensile strengths above 10.9 MPa and strain capacities of 0.25–0.30%, including a pronounced strain-hardening regime. Under drop-weight impact loading, specimens absorbed more than 40 J of energy without catastrophic fragmentation. Ultrasonic pulse velocity averaged 5344 m/s, indicating a dense and well-integrated microstructure. Overall, the results confirm that the investigated UHPC functions as a fracture-resistant structural composite in which tensile capacity, fiber-controlled crack bridging, and energy dissipation govern performance across multiple loading modes. Full article

The increasing accumulation of mine tailings has motivated the development of sustainable strategies for their reuse within the framework of the circular economy. This study evaluates the mechanical performance of four laboratory-cast concrete mixtures: a reference mixture, a mixture in which copper tailings were incorporated at 8% of the base mixture mass to replace an equivalent mass of natural coarse sand, and two tailings-based mixtures reinforced with 0.4% and 1.2% steel fibers. Their compressive strength and elastic modulus were evaluated after 7, 14, 28, and 100 days of curing to assess the mechanical performance of the proposed mixtures and their potential relevance for underground mining support applications. The results showed that after 100 days, the 8% copper tailings mixture reached a compressive strength of 41.6 MPa, compared with 39.6 MPa for the conventional mixture. The addition of steel fibers produced a slight reduction in compressive strength and stiffness at early curing ages; however, comparable mechanical performance was achieved after extended curing. The observed improvements are primarily consistent with the filler effect and improved particle packing associated with the fine tailings fraction, although the underlying microstructural mechanisms were not directly evaluated in this study. Overall, the results provide preliminary evidence that copper tailings can be incorporated into laboratory-cast concrete mixtures with steel fibers, supporting their further evaluation for potential underground support applications. Full article

Fiber-reinforced polymers (FRPs) are increasingly adopted in structural rehabilitation due to their high strength-to-weight ratio, corrosion resistance, and ease of installation, making them suitable for extending the service life of reinforced concrete (RC) infrastructure. Studies on shear strengthening with CFRP was early focused on externally boning (EB) showed premature delamination between fiber and concrete which limits the bonding strength. Hence, this study experimentally evaluates the shear strengthening behavior of RC beams retrofitted using inside-groove bonded CFRP and hybrid techniques. A total of seven beam specimens with identical geometry, internal reinforcement layout, and concrete strength were fabricated and tested under four-point bending to generate a well-defined shear-critical region. The experimental program focused on directly comparing bonding configurations while also examining the influence of groove depth (10 mm and 15 mm) and steel anchorage for concrete cover on structural response and failure mechanisms. The strengthened specimens achieved ultimate load increases ranging from approximately 10% to 23% relative to the control beam. Variation in groove depth within the investigated range did not significantly influence shear capacity, indicating that moderate groove penetration is sufficient to develop effective mechanical interlock. Steel anchors were introduced to restrain concrete cover separation and improve confinement of the bonded region and substantially increase peak load, it successfully mitigated premature cover delamination near stirrup locations and altered the governing failure mode. Full article

Grouted connection segments are key load-transfer components in offshore wind jacket structures, and their axial compressive performance is essential for the safety and reliability of the foundation system. This paper develops a finite element model of a grouted connection segment incorporating steel-fiber-reinforced high-strength grout to investigate its mechanical behavior and parametric effects under axial compression. A 1:7-scale model test is conducted to verify the numerical model through comparisons of the load–displacement response and strain responses at key locations. The steel tubes are simulated using a trilinear hardening elastoplastic model, while the steel-fiber-reinforced high-strength grout is represented using the concrete damaged plasticity model with corresponding tensile and compressive constitutive relationships and damage parameters to characterize its nonlinear response. Based on the validated model, a full-scale numerical model is established to analyze the effects of steel tube thickness, shear key spacing, shear key height, and shear key width using the control variable method. The results indicate that steel tube thickness has the most significant influence on the ultimate bearing capacity and can improve the load-bearing capacity and ductility of the structure. Shear key spacing mainly affects axial stiffness and deformation compatibility, while shear key height and width have limited effects on the ultimate bearing capacity but contribute to local deformation control and stiffness enhancement. The findings provide a validated numerical basis for evaluating the axial compressive behavior of steel-fiber-reinforced grouted connections and offer a useful reference for the design and parameter optimization of grouted connection segments in deep-water offshore wind jacket structures. Full article

Typical specifications for steel fiber-reinforced shotcrete primarily focus on early-age mechanical properties and do not provide much guidance on evaluating changes in capacity over time, particularly under humid underground service conditions. In addition, accelerated laboratory durability tests are rarely calibrated against measurements obtained from underground structures in service. This study addressed that gap with a 12-month dual-track approach: (i) maintaining controlled near-saturated conditions in the laboratory at 23 ± 2 °C and 95–100% relative humidity, with subsequent evaluation of the mechanical properties (compressive strength, splitting tensile strength, and single-fiber pull-out resistance) at 0, 3, 6, 9, and 12 months; and (ii) monitoring the compressive strength in three operating underground silver mines in Zacatecas, Mexico, using the mean 48 h production-control strength as the field reference and cores taken after approximately 12 months of service. The three laboratory trajectories were well described by first-order exponential models (R² ≥ 0.99) throughout the 12-month monitoring period. The observed reductions were 22.0% for compressive strength, 21.4% for splitting tensile strength, and 26.3% for single-fiber pull-out resistance. The apparent pull-out rate constant was approximately 18% higher than the compressive-strength rate constant, though the mechanism for this difference was not identified independently. In the field, there was an apparent reduction in compressive strength of 8–10% after about 12 months. Comparison of the chamber and field compressive-strength rates produced an apparent acceleration factor, AF ≈ 2.7, with a per-mine range of 2.4–3.0. The high pairwise correlations among the three laboratory properties (r ≥ 0.996) and the first PCA component, which explained 99.8% of their standardized trajectory variance, reflected closely aligned temporal trends. However, since these were based on five exposure-age means, they should be considered only exploratory evidence of co-variation rather than causation. MANOVA demonstrated significant multivariate effects on the combined compressive and splitting tensile responses across exposure ages (p < 0.001). The proposed acceleration factor is preliminary and restricted to the materials, sites, exposure context, and observation period studied. Routine compressive-strength core testing may be useful as a practical screening indicator, but it cannot quantitatively replace direct bond or post-cracking evaluation. Full article

Low-frequency vibration of thin-walled materials, which are widely used in aircraft, can lead to fatal damage of aircraft components and even serious accidents. Although active vibration suppression using macro fiber composite (MFC) holds promise, the weak internal interfaces of MFC—specifically, those among the piezoelectric ceramics, the polymer matrix, and the interdigitated electrodes—seriously restrict the actuation strain and effective suppression bandwidth, limiting its engineering application under broadband aerodynamic excitation. In this work, an MFC-based self-feedback device integrating sensor and actuator is proposed. To address this, the performance bottleneck of the MFC actuator is overcome through a combined interface modification strategy combining plasma etching and dopamine-inspired modification. The interfacial modification elevates the maximum actuation strain of the MFC from 915 με to 1105 με (an increase of 20.8%). When applied to an aluminum cantilever beam, a vibration suppression ratio of 98.11% is achieved at the resonant frequency (75 Hz), and the effective suppression bandwidth (suppression ratio > 50%) reaches 77 Hz. Notably, this strategy is effective on aluminum, stainless steel, and carbon fiber substrates, as equally efficient broadband suppression is realized on all three materials. A powerful pathway is thus provided to unlock the full potential of MFC for low-frequency, broadband active vibration control in aerospace applications. Full article

Accurate high-temperature field characterization is important for explosion diagnostics, laser–matter interaction, combustion monitoring, and related thermal processes. This work presents an integrated thermometry framework combining fiber-optic spectrometry with monochrome imaging. Its central contribution is not a new multispectral principle or optimization algorithm, but an integration-time-dependent radiometric calibration framework coupled with representative spectral-emissivity transfer under clearly stated applicability conditions. Its central element is a three-parameter radiometric calibration model in which camera integration time is explicitly included, so that radiance conversion can be performed across the experimentally calibrated integration-time range without repeating a separate fixed-exposure calibration for each setting. Multiwavelength spectral radiance is used to jointly retrieve temperature and a continuous, second-order polynomial emissivity function with a genetic algorithm serving as the global optimizer. The emissivity function obtained from a representative spectral sampling region is then transferred to the imaging model for pixelwise temperature inversion; this step assumes that the material and surface state are sufficiently uniform over the region to which the function is applied. The method is examined using steady-state tungsten–halogen-lamp measurements with nominal color temperatures of 2200–2800 K and a transient laser-heated 316L stainless-steel case. Agreement with a Wien-based estimate is used as an internal spectral-consistency check rather than as an independent traceable accuracy validation. In the transient case, the retrieved spectral-field-of-view temperature increased from 2311.9 to 2398.5 K over 50–60 s, and the reconstructed images reproduced the corresponding increase in the central high-temperature region. The present results demonstrate the feasibility of coupling integration-time-dependent calibration with measured spectral-emissivity transfer for two-dimensional temperature reconstruction, while the achievable absolute accuracy remains subject to detector linearity, emissivity-model validity, spatial emissivity uniformity, radiometric calibration, and independent reference validation. Full article

Lithium slag-based geopolymer (LSG) provides a promising route for the high-value utilization of lithium slag; however, its pronounced shrinkage deformation continues to restrict engineering applications. To clarify the multi-scale mechanism by which fibers regulate LSG shrinkage, this study investigated the effects of single and hybrid additions of carbon nanotubes (CNTs) and hooked-end steel fibers (HSFs). The 90 d drying shrinkage test quantified shrinkage-reduction efficiency for mono- and hybrid-fiber systems. MIP was used for porosity and pore size distribution analysis; SEM examined fiber dispersion, interfacial bonding, and CNT-HSF synergy. At 90 d, 0.15% CNTs and 1.5% HSFs reduced shrinkage by 5.7% and 26.8%, respectively, whereas the C0.15-H1.5 hybrid mixture achieved a maximum reduction of 31.33% relative to the control. HSF addition increased porosity from 15.5% to 23.1% and the average pore diameter from 23.36 to 50.82 nm. Macroscopic shrinkage was reduced because interfacial friction and hooked-end anchorage provided mechanical restraint. In addition, based on fiber pull-out behavior and a simplified interfacial bond-slip model, the effective confinement radius at the fiber–matrix interface was analyzed, and the concept of fiber-confined zones was proposed. Results show that CNTs refine pore structure and bridge microcracks, whereas HSFs provide mechanical restraint through interfacial friction and anchorage. The hybrid CNT-HSF system achieved a maximum drying shrinkage reduction of 31.33%, higher than the corresponding theoretical additive value. The spatial overlap of fiber-confined zones is identified as the key mechanism for forming a weakly rigid framework that suppresses macroscopic shrinkage. Full article

This research evaluates the seismic resilience of lifeline bridge columns in Vancouver, British Columbia, by comparing traditional reinforced concrete (RC) columns with an equivalent circular concrete-encased steel (CES) system. Designed to meet the stringent performance-based requirements of CSA S6-25 and the BC Ministry of Transportation and Infrastructure (MoTI) Supplement, the structures were analyzed under a suite of ground motions representing the complex crustal, subcrustal, and subduction hazards of the Pacific Northwest. Nonlinear fiber-discretization modeling, validated against experimental data, was employed to assess damage progression and serviceability limits through comprehensive pushover, moment-rotation, and nonlinear time-history analyses. The results demonstrate that while both systems satisfy lifeline criteria, the CES configuration provides a superior safety margin due to the presence of the encased structural steel core. This internal steel member maintains vertical load capacity and extends the stable displacement plateau beyond the capacity of conventional RC, effectively reducing reinforcement strain and facilitating immediate post-seismic recovery. These findings highlight circular CES piers as a highly resilient alternative for critical transportation infrastructure in high-seismicity regions. Full article

To address the challenge of deformation control in operating tunnel structures, this study investigates a novel reinforcement method for operating shield tunnels using a basalt-fiber-reinforced polymer-wrapped concrete-filled steel tube (BFRP-CFST) composite profile. Two primary study variables were considered. At the segment level, the reinforcement condition comprised two levels: unreinforced and BFRP-CFST-reinforced, with three replicate specimens at each level (US-1 to US-3 and RS-1 to RS-3, respectively). At the full-ring level, the number of installed composite profile frames comprised five levels (n = 0, 1, 2, 3, and 4), where n = 0 represented the unreinforced reference condition. A combined experimental and numerical framework was established, including full-scale four-point bending tests on individual tunnel segments and finite element simulations of full-ring linings. Experimental results demonstrate that the ultimate bearing capacity of reinforced segments increased from 534.4 kN to 921.3 kN, corresponding to a 72.4% improvement. The load level before visible cracking increased by 84.2%. At maximum crack widths of 0.2 mm and 2.0 mm, the mid-span displacement of the reinforced segments was reduced by 30.0% and 21.4%, respectively. The test observations indicate that the prefabricated composite profiles effectively delayed crack development and improved the post-cracking stiffness of the segment. Full-ring numerical simulations further showed that installing one to four composite profile frames increased the external load corresponding to a convergence displacement of approximately 10.5 cm by 12.4%, 21.1%, 28.5%, and 37.4%, respectively. Scientifically, the results reveal a staged load-transfer process in which adhesive bonding provides distributed load transfer during the initial response, while mechanical anchors maintain residual load transfer after local interface debonding; they also establish a quantitative relationship between the number of profile frames and full-ring convergence resistance. From an applied engineering perspective, the proposed profile increased the ultimate load and crack-initiation load of the segments by 72.4% and 84.2%, respectively, while its lightweight and prefabricated configuration provides a potentially rapid rehabilitation option for operating shield tunnels. Full article

The combined use of recycled aggregate concrete (RAC) and basalt fiber-reinforced polymer (BFRP) bars offers a promising sustainable and corrosion-resistant solution for reinforced concrete structures. However, the inferior quality of recycled aggregates and the relatively low elastic modulus of BFRP bars can compromise the mechanical and flexural performance of RAC members. To address these issues, hybrid fiber-reinforced recycled aggregate concrete (HFRAC) incorporating polyvinyl alcohol (PVA) and steel fibers was developed, and its mechanical and flexural performances were experimentally investigated. The basic mechanical properties of conventional Portland cement concrete (PC), fiber-free RAC, and RAC with hybrid fiber (HF) contents of 0.6%, 0.9%, 1.2%, and 1.5% were first evaluated. A total of nine beams were subsequently tested under four-point bending to investigate the effects of HF content (0–1.5%) and BFRP reinforcement ratio (0.48–1.98%) on flexural behavior. The results showed that an HF content of 1.2% provided the best performance among the investigated fiber contents at both the material and structural levels. At the material level, compared with RAC, 1.2% HF increased the cube compressive strength, axial compressive strength, elastic modulus and splitting tensile strength by 19.44%, 23.08%, 11.39% and 32.55%, respectively. The incorporation of HF effectively mitigated the mechanical deterioration caused by recycled aggregates, allowing HFRAC to achieve comparable or improved basic mechanical properties relative to RAC. At the structural level, compared with the fiber-free RAC beam, the beam with 1.2% HF exhibited increases of 132.51% and 11.92% in cracking and ultimate loads, respectively, and a 47.9% reduction in crack width, while also demonstrating improved flexural performance compared with the PC beam under the investigated conditions. Three failure modes were observed, namely BFRP bar rupture, balanced failure, and concrete crushing, with balanced failure occurring at a reinforcement ratio of approximately 1.0–1.1%. The hybrid fibers effectively refined cracks through a bridging effect, demonstrating superior crack control compared to increasing the reinforcement ratio alone. This study offers valuable insights into improving the performance of RAC and facilitating the wider adoption of BFRP bars in structural applications. Full article

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete (RC) structures exposed to aggressive environments. Although fiber-reinforced polymer (FRP) reinforcement provides excellent corrosion resistance, its confinement effectiveness in RC columns has not been fully understood. This study experimentally investigated the axial compressive behavior of rectangular RC short columns reinforced with steel, carbon fiber-reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP) bars. Ten specimens with different reinforcement types and stirrup configurations were tested under monotonic axial compression to evaluate compressive strength, axial strain response, deformation behavior, failure mechanisms, and confinement performance. The results indicated that the contribution of FRP reinforcement depended on the reinforcement configuration and confinement mechanism. Specimens reinforced with CFRP longitudinal bars exhibited higher axial capacity than the steel-reinforced control specimen within the tested configurations; however, the influence of the longitudinal reinforcement ratio should also be considered. GFRP stirrups exhibited confinement behavior comparable to CFRP stirrups, whereas CFRP stirrups experienced premature fracture at bent corner regions, which reduced their confinement effectiveness and deformation capacity. Reducing stirrup spacing from 150 mm to 75 mm provided limited improvement in compressive strength because of premature stirrup failure and insufficient development of confinement effects. Existing confinement models tended to overestimate the post-peak response of FRP-reinforced columns. These preliminary findings provide experimental insights into the confinement behavior of FRP-reinforced concrete columns and contribute to the development of improved analytical models. Full article

To evaluate the influence of fiber content, temperature, and loading rate on the dynamic compression performance of ultra-high performance concrete (UHPC), orthogonal Split Hopkinson Pressure Bar (SHPB) tests were performed on 120 MPa UHPC specimens. Range analysis of the test data reveals that the steel fiber content exerts the largest range on dynamic compressive strength, with loading rate ranking second and temperature having the least effect. A three-dimensional mesoscopic finite element model that accounts for temperature-dependent behavior was developed using a modified Karagozian & Case (K&C) constitutive model together with high-temperature bond–slip degradation curves. The simulated peak stresses are generally higher than the experimental values, with a Root Mean Square Error of 9.02 MPa, a Normalized Root Mean Square Error of 4.65%, and a maximum discrepancy of 10.07%, while the major experimental failure characteristics are reasonably reproduced. Additional numerical simulations indicate that the influence of steel-fiber content becomes increasingly temperature-dependent. Within the experimentally investigated range up to 300 °C, higher fiber content generally improves dynamic response and specimen integrity. At 600~800 °C, the numerical extrapolations suggest that the reinforcing efficiency of steel fibers may be substantially reduced under the assumed temperature-dependent degradation conditions. These high-temperature trends require further experimental validation. Full article

This study investigates the compressive performance of fiber-reinforced polymer (FRP) rebar-reinforced Seawater and Sea Sand Concrete (SSC) columns through an integrated approach combining finite element analysis, theoretical derivation, and machine learning. Finite element models were developed to quantify the influence of key parameters on the ultimate bearing capacity and lateral deflection. The results indicate that the compressive capacity decreases significantly with increasing eccentricity and slenderness ratio. Columns reinforced with steel rebars demonstrated superior load-bearing and anti-lateral displacement capabilities compared to their FRP-reinforced counterparts. A theoretical formula for predicting the compressive capacity was derived; however, it systematically overpredicted the experimental measurements by approximately 36%. To develop data-driven predictive models for the ultimate load capacity of FRP–SSC columns, four machine learning models, backpropagation neural network (BPNN), bootstrap aggregating BPNN (Bagging-BP), genetic algorithm-optimized BPNN (GA-BP), and gradient boosting regression trees (GBRT), were employed. Using sectional dimension, concrete strength, reinforcement parameters, eccentricity, and slenderness ratio as inputs, the validation sets of the models achieved R-values of 0.942, 0.918, 0.933, and 0.990, respectively. Feature importance analysis based on SHAP identified eccentricity as the most influential parameter. Results from this work can help to understand the behavior of FRP–SSC columns under compression. Full article