Search Results (1,350)

To improve the rutting resistance and low-temperature cracking performance of polymer-modified asphalt under extreme conditions, hierarchically structured ZnO-loaded porous activated carbon (ZnO/PAC) nanosheets were introduced as a synergistic reinforcing agent for SBS-modified asphalt. The ZnO/PAC hybrids were synthesized via template-assisted carbonization followed by hydrothermal growth, and their effects were evaluated by microscopic characterization and rheological tests, including temperature sweeps, multiple stress creep and recovery (MSCR), and bending beam rheometer (BBR) analyses. ZnO was successfully anchored onto the PAC, forming a three-dimensional flower-like nanostructure. Among the investigated samples, ZPS3 with 3 wt.% ZnO/PAC showed the best overall performance. At 64 °C, the rutting factor increased from 4.2 kPa for the SBS-modified asphalt to 6.8 kPa for ZPS3, representing a ~62% enhancement and indicating markedly improved high-temperature deformation resistance. MSCR results further confirmed the superior rutting resistance of ZPS3, which exhibited the highest recovery and the lowest non-recoverable creep compliance. In addition, BBR results showed that the low-temperature performance grade improved from −12 °C for conventional the SBS-modified asphalt to −18 °C for the ZnO/PAC-modified system. These results demonstrate that ZnO/PAC nanosheets can effectively enhance both the high-temperature rutting resistance and low-temperature cracking resistance of SBS-modified asphalt. Full article

Due to excellent performance, polytetrafluoroethylene (PTFE), being sealing material, is widely used in chemical engineering, aerospace engineering, mechanical engineering, civil engineering, energy engineering and other sectors. However, due to obvious temperature drops in supplying or storing fluids, the mechanical behavior of PTFE under cryogenic conditions is still unclear. In this study, the creep mechanical performance of PTFE gaskets after cryogenic aging in liquid oxygen is experimentally investigated. The circular PTFE gasket samples are immersed into liquid oxygen for cryogenic aging treatment. The universal testing machine is utilized for material mechanic tests. Three different load levels, including 10 MPa, 15 MPa and 20 MPa, are designed and accounted for. It is found that the creep strain of PTFE exhibits three typical stages, namely the initial rapid increase phase, transition phase with a reducing growth rate, and stable linear growth phase. Moderate cryogenic immersion aging can effectively improve the creep resistance of PTFE, but excessive aging treatments will lead to mechanical property degradation of PTFE. The Burgers life prediction model is improved by introducing a nonlinear correction term, which can accurately predict the creep behavior of PTFE under different aging states. The present study can provide experimental evidence and a theoretical basis for a deep understanding of the mechanical response of PTFE materials under extreme cryogenic intermittent service conditions. Full article

Residual stress is an inherent consequence of the welding process and can significantly compromise the structural integrity of welded components. To clarify the high-temperature creep damage evolution of the 600 MPa-grade ship hull structural steel base metal, high-temperature creep tests were conducted, aiming to improve the understanding of its deformation behavior and to support reliable numerical predictions. The experimentally calibrated creep constitutive model was subsequently integrated into finite element simulations to analyze the residual stress evolution in welded joints and to quantitatively evaluate the effects of post-weld heat treatment (PWHT) and hammer peening. The results indicted that, within 450–550 °C, creep deformation of the steel was dominated by dislocation glide and climb, while creep damage was mainly associated with void and crack formation. The simulation results revealed that residual stresses were predominantly concentrated in the weld metal and the heat-affected zone, with the peak von Mises stress in the as-welded joint reaching 686.5 MPa, exceeding the material’s yield strength at the simulated temperature. PWHT exhibited superior stress-relief effectiveness compared with hammer peening, markedly reducing the peak residual stress. Moreover, the stress-relief behavior showed a nonlinear dependence on both holding time and heat-treatment temperature. In contrast, hammer peening produced a localized stress-relief effect, confined primarily to the mechanically impacted region. These findings provided a theoretical foundation for optimizing post-weld treatment strategies to mitigate residual stress in the high strength steel welded joints. Full article

Many existing reinforced concrete (RC) structures have undergone increases in service loads due to changes in use, functional upgrades, and evolving design codes. This highlights the need for reliable requalification methods that account for long-term degradation mechanisms, particularly those related to sustained loading and creep. This study investigates the residual flexural behavior of RC beams after long-term loading and evaluates its effects on stiffness and ultimate strength. Three RC beams were loaded to 43% of their short-term yielding moment and kept under sustained load for 210 days, while three identical specimens were maintained as unloaded references. Afterward, all beams were subjected to repeated four-point loading–unloading cycles to detect changes in stiffness, strength, and cyclic response. The results indicate that long-term loading did not significantly affect the beams’ ultimate load-carrying capacity compared with the reference specimens. However, the long-term-loaded beams exhibited a clear reduction in initial stiffness. This difference was most evident during the first loading cycle and gradually decreased in subsequent cycles. To interpret these findings, a layered fiber model was developed to simulate cyclic behavior while incorporating time-dependent concrete effects. The model successfully reproduced the main experimental trends, reinforcing the reliability of both the testing program and the analytical approach. The study enhances understanding of stiffness degradation in RC elements subjected to increased service loads. Full article

Ultra-high-performance concrete (UHPC) is widely used due to its strength, toughness, and durability. Shrinkage issues are the primary cause of concrete cracking and one of the main factors limiting the widespread application of UHPC in structural engineering. The shrinkage properties of UHPC vary depending on curing conditions. Research indicates that after thermal curing, the pore structure of UHPC is optimized, resulting in a significant reduction in shrinkage values. Based on the superposition principle, temperature creep coefficients and humidity creep coefficients are introduced to correct the temperature and humidity in the test environment to a constant temperature (20 °C) and humidity (75% relative humidity). The B3 coefficient of variation method was used to compare five different creep prediction models. The CEB-FIP2010 model was selected as the benchmark creep model, and curing condition coefficients were incorporated into the model to establish a comprehensive creep calculation model considering curing conditions. After 550 days of steam curing, the shrinkage strain of the UHPC specimens was approximately 28.9% of that of the uncured specimens. The additional creep deformation caused by temperature and humidity in the uncured and steam-cured specimens accounted for approximately 10% and 20% of the total creep deformation over 550 days, respectively. The strain development rates for both tensile and compressive strains in steam-cured specimens were lower than those in uncured specimens. A ten-year long-term creep simulation of UHPC precast joint beams was conducted using the finite element software Midas-Fea, and the comparison results validated the reliability of the comprehensive creep model. Full article

While the utilization of waste polymers in asphalt mixtures is widely studied, the specific influence of additive geometry on performance mechanisms remains underexplored. This study presents a multi-scale performance assessment of asphalt mixtures modified with waste Polyvinyl Chloride (PVC) foils. Waste PVC foils were processed into two distinct geometries, “Wiry” and “Random”, and incorporated into mixture at dosages ranging from 5% to 12.5% by weight of bitumen via the dry process. At the macro-scale, Semi-Circular Bending, Hamburg Wheel Tracking, Repeated Creep, and Modified Lottman tests were conducted. At the micro-scale, Scanning Electron Microscopy and EDS analyses were employed to investigate interfacial adhesion. The results demonstrated that the “Wiry” geometry significantly outperformed the “Random” by establishing a three-dimensional reinforcement network. Specifically, the mixture modified with 7.5% “Wiry” PVC yielded the highest Flexibility Index of 24.17, representing a 3.7-fold improvement. Furthermore, this optimum dosage enhanced high-temperature stability and maintained moisture resistance (TSR > 85%), whereas dosages exceeding 10% caused agglomeration and performance loss. Microstructural imaging indicated that the fibrous morphology and calcite-rich surface of the “Wiry” additive facilitate superior mechanical interlocking. Consequently, this study suggests that optimizing waste PVC geometry is as critical as dosage for maximizing the durability and sustainability of flexible pavements. Full article

This study investigates the synergistic effects of combining polyphosphoric acid (PPA) and styrene–butadiene–styrene (SBS) as modifiers in asphalt binders to enhance their performance. The research focuses on optimizing the concentrations of PPA and SBS to improve the resistance to permanent deformation, cracking at intermediate and low temperatures, and resistance to aging. A series of empirical and rheological tests, including penetration, softening point, elastic recovery, dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), and bending beam rheometer (BBR), were conducted to evaluate the rheological and engineering properties of the modified binders. The results indicate that PPA can partially replace SBS, offering comparable improvements in high-temperature performance and creep resistance. The MSCR test revealed a statistically significant synergistic effect between PPA and SBS, resulting in improved recovery and reduced non-recoverable compliance. However, PPA alone shows limited effectiveness at low temperatures and in properties that are governed by elastic response. This study highlights the potential for optimizing asphalt modifiers by leveraging the complementary properties of PPA and SBS in hybrid systems, particularly regarding high-temperature properties and dynamic loading. Full article

The rheological behavior of rock masses governs long-term stability, yet the time-dependent properties of grouted structural planes remain insufficiently quantified. Graded shear creep tests were conducted on artificially split sandstone structural planes with controlled grout thicknesses, complemented by scanning electron microscopy (SEM), to clarify creep evolution and long-term shear strength. The results show that the total shear creep displacement of grouted specimens exhibits limited sensitivity to grout thickness, while the ratio of long-term to theoretical shear strength increases by approximately 10% at a grout thickness of 2 mm; this strengthening effect, however, diminishes at greater thicknesses. Moreover, the creep rate evolution of grouted specimens differs fundamentally from that of ungrouted specimens, with about 60% of grouted samples exhibiting an accelerated creep stage characterized by a U-shaped rate curve. The failure mode shifts from asperity-controlled slip in ungrouted structural planes to damage concentrated at the grout–rock interface in grouted specimens. SEM observations further reveal that micro-defects at this interface initiate and propagate cracks, ultimately governing the macroscopic creep failure process. Overall, this study establishes an isochronous curve-based method for determining long-term strength and demonstrates that interface micromechanics critically control the long-term performance of grouted rock masses. These findings provide practical guidance for grouting reinforcement in underground engineering. Full article

Background: Evaporative water loss from burn wounds is a major but often neglected component of early fluid requirements. Despite its physiological importance, no dedicated review has quantified acute post-burn evaporative water loss (TEWL) and its interaction with modern resuscitation strategies in over 40 years. Recent mass-casualty burn events in specialized centers have re-emphasized the clinical importance of accurate early fluid balance, which is particularly challenging. Methods: A scoping review (PRISMA-ScR) of historical quantitative studies and 23 contemporary (2015–2025) adult major-burn resuscitation cohorts was conducted. Expected TEWL was derived from Lamke benchmarks; interstitial edema was estimated from the only available regression of simultaneous fluid input and 24 h weight change. A novel TEWL/edema ratio was tested against resuscitation volume (mL/kg/%TBSA) and the established input/output (I/O) ratio. Results: In the acute phase, the median TEWL normalized to total body surface area was 71 mL/m²/h [52–79 mL/m²/h], allowing for calculation of the TEWL/edema ratio. The TEWL/edema ratio was inversely correlated with the resuscitation fluid dose (R² = 0.811) and the I/O ratio as well (R² = 0.86), crossing unity at 2.85 mL/kg/%TBSA. A ratio > 1 signals high evaporative drive and/or possible under-resuscitation; a ratio < 1 alerts to fluid creep before significant weight gain. Conclusions: The TEWL/edema ratio is the first physiology-grounded, easily calculable resuscitation endpoint that complements urine output by providing insight into whether administered fluid is lost as obligatory evaporation or sequestered as edema. Routine estimation of expected TEWL and early monitoring of the TEWL/edema ratio may help guide goal-directed burn resuscitation, especially when early excision is delayed or impossible. Given the substantial inter-individual variability, the ratio derived from aggregate data should not be interpreted as a patient-specific predictor. Full article

Understanding the evolution of coal pore–fracture structures under coupled stress paths and creep deformation is critical for enhancing coalbed methane extraction and preventing coal and gas outbursts. In this study, coal samples from the Ningtiaota Mine were investigated using online Nuclear Magnetic Resonance (NMR) technology combined with triaxial loading–creep coupled experiments. The dynamic evolution of pore–fracture structures (PFSs) under different deviatoric stress levels was characterized and visualized in real time and across multiple scales. The results reveal a pronounced stress-dependent pore evolution during creep. Under low-stress conditions, seepage pores were compressed and gradually transformed into adsorption pores, whereas under high-stress conditions, seepage pores expanded and interconnected, dominating deformation and failure. Fractal theory was employed to quantify pore structure complexity, and repeated experiments demonstrated a significant positive correlation between the fractal dimension and the fractional order. Based on these findings, a fractal-dimension-based fractional creep model was developed by introducing a Riemann–Liouville fractional dashpot. The proposed model accurately captures the nonlinear creep behavior of coal and provides a microstructural interpretation of the fractional order. This study provides theoretical and experimental support for long-term stability assessment of deep coal–rock masses and prediction of coalbed methane migration. Full article

In this study, an L₁₆(4³) orthogonal experimental design was employed to optimize the preparation process of rubber-modified asphalt, and a series of rheological tests were conducted using a dynamic shear rheometer to systematically investigate the compatibility mechanisms among the four components: base asphalt and rubber particles. The results indicate that process parameters exert varying degrees of influence on performance. The optimal combination determined was: base bitumen temperature of 170 °C, shear rate of 4000 r/min, and shear time of 40 min, followed by isothermal curing at 170 °C for 60 min. Rheological analysis indicates that resin and asphalt are the key components determining the high-temperature rheological properties of rubber-modified asphalt; notably, L74, which has the highest asphalt content, exhibits excellent high-temperature performance. Grey correlation analysis shows that the correlation coefficient between resin content and creep recovery capacity is 0.82, while the correlation coefficient between asphalt content and resistance to permanent deformation is 0.86. Furthermore, the goodness-of-fit value of the multiple regression model exceeded 0.99, further confirming the reliability of the research results. This study provides a precise characterization of compatibility, thereby offering a theoretical foundation and technical support for material selection and process control in the application of rubber-modified asphalt. Full article

This article compares the analytical results from two models, based on the theory of hereditary creep strain, with experimental results on the rheological properties of lightweight sintered aggregate concrete under cyclically varying loads. In a previous article, the authors analyzed the adequacy of standard models for the same test results. Because the use of standard models is very complex and does not improve the approximation of test results without additional calibration, the authors suggest reconsidering the use of hereditary models for LWAC. The application of four such long-term models was analyzed. Among these models, the Arutiunian theory of hereditary creep with aging and the modified hereditary theory with Bažant aging function yielded quantitatively and qualitatively correct results. The application of hereditary creep theory allowed for the formulation of the total strain as a superposition of strain increments, obtained by an integral equation. This equation was applied to a series of constant stress increments and decrements, as in the case of cyclic loading, and it was mathematically described in segmented form. Knowledge of the properties of LWAC and useful long-term models is essential for the design of prestressed structures made of lightweight aggregate concrete subjected to time-varying loads. Full article

The occurrence of shear creep in polyethylene under applied stress results in deformation, which restricts the service life of the final product. However, the factors influencing shear creep and its underlying mechanisms remain unclear. This article investigates the effects of average molecular weight and comonomer on the shear creep behavior and underlying mechanisms of high-density polyethylene (HDPE). The materials chosen were HDPE with weight-average molecular weights (Mw) of 148,100, 191,800, 226,500, 252,700 and 325,100 g/mol, as well as copolymers incorporating propylene or octene as comonomers. The results indicate that creep deformation decreases with increasing Mw, and that polyethylene copolymers incorporating propylene and octene cause increased creep deformation compared to homopolymers. Dynamic mechanical analysis (DMA) and rheological testing were used to investigate the influence of Mw and comonomer on shear creep behavior. The experimental results demonstrate that increasing the weight-average molecular weight enhances molecular chain entanglement, thereby improving creep resistance. The incorporation of comonomers introduces branches into the polyethylene structure, reducing entanglement density and leading to diminished creep resistance. This study provides valuable insights and references for the development of polyethylene materials that resist shear creep. Full article

Recent studies have shown that a new family of Ni-based superalloys with high Ta and high Hf contents exhibits a promising property profile and may be able to fill the gap between creep-resistant alloys and those processable by PBF-LB/M. The effect of simultaneously high Ta and Hf contents on oxidation resistance has not yet been investigated and is addressed qualitatively in this study. Isothermal oxidation tests were conducted in air at 950 °C for 100 h, 300 h, and 500 h. After cooling, the weight change and cross-sections of the specimens were examined. The study shows that the Hf-free alloy exhibits severe spallation of the Al-oxide and Cr-/Ni-oxide layer. The Hf-containing alloys exhibit improved oxide layer adhesion and a promoted formation of a continuous Al-oxide layer, which is attributed to the early formation of Hf-oxide particles. Furthermore, the addition of Hf influences the morphology of internally oxidized Al, which grows preferentially parallel to the surface rather than perpendicular to it. This behavior leads to effective protection of the alloys by an Al-oxide layer, either external or internal, which is remarkable considering the moderate Al content of only 3 wt.%. Full article

In response to the shortcomings still observed in polyethylene (PE)/ethylene-vinyl acetate (EVA)/styrene-butadiene-styrene (SBS) composite modified bitumen regarding storage stratification and low-temperature performance, this paper further introduces furfural extract, elemental sulphur, stabilisers and Z-6036 into this ternary system, and employs orthogonal design to screen the additive ratios. Tests were conducted on conventional physical properties, rotational viscosity, dynamic shear rheology and bending beam rheology, focusing on the material’s temperature sensitivity, rheological behaviour, low-temperature creep resistance and phase characteristics. The modification effects were analysed using fluorescence microscopy, scanning electron microscopy and infrared spectroscopy. Compared with the control group composed of 4% PE, 4% EVA and 2% SBS, the samples obtained from the orthogonal design showed an increase in elongation at 5 °C ranging from 52.5% to 213.9%; the difference in softening points decreased from 35.2 °C to a minimum of 0.1 °C, indicating improved storage stability. The temperature sensitivity of all sample groups was reduced, with the optimal group achieving a VTS of −0.4413, representing a 46.7% improvement over the control group. At −12 °C, the m-values of all nine orthogonal samples were higher than those of the control group, with seven groups reaching m ≥ 0.3, indicating improved low-temperature stress relaxation capability. A comprehensive analysis of the experimental results indicates that the selected chemical additives are beneficial for optimising the dispersion state and compatibility of the SBS/PE/EVA ternary modified bitumen, whilst also balancing rheological properties and low-temperature crack resistance to a certain extent. Microscopic and spectroscopic analyses further suggest that internal interactions within the system have been enhanced and the phase distribution has become more uniform; however, the current evidence is insufficient to conclusively determine that a specific form of chemical cross-linking reaction has occurred. Full article