Materials and Structures最新文献

Warm rubberized bitumen (WRB) is a commonly used sustainable material of asphalt pavement in Europe and United States. At present, macroscopic nonlinear rheological properties and microscopic characteristics of WRB samples considering the effect of wax compound structures remain unclear. This paper aims to reveal the potential correlation between the macroscopic non-linear rheological properties and microscopic characteristics of WRB through the combination of rheological tests and microscopic analysis methods. The results show that wax-based additives with higher melting points can crystallize at room temperature to cause the phase separation in WRB system, which can be linked to that nonlinear rheological behaviors of long carbon chain C40 and Sasobit waxes advance the nonlinear stage of the viscosity-temperature curve and reduce linear viscoelastic (LVE) limit compared with short-chain C18 and C24 waxes. The inactivated crumb rubber (CR) has evident phase separation and chemical activation can reduce the average size, area proportion and average number of phase separation due to CR, which can be related to the enhanced nonlinear rheological properties of bitumen after CR addition and deterioration of nonlinear rheological performance of CR after chemical activation. The thermal transition behaviors due to wax crystallization happen at relatively low temperature during the cooling, which can also be associated with more obvious nonlinear performance of WRB sample due to wax crystallization in a low temperature environment. The research results can enhance the understanding of non-linear rheological behaviors and microscopic mechanisms and give guidance for the performance optimization of WRB.

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This study addresses the critical gap in fire safety standards for rubber-modified concrete (RMC) by developing the first fully coupled thermo-mechanical model that integrates rubber pyrolysis kinetics with interfacial stress evolution—a critical advancement over existing uncoupled frameworks that neglect phase-change interactions. Unlike conventional concrete models (e.g., Eurocode 2), our framework uniquely captures void-induced thermal insulation effects and CTE mismatch mechanisms specific to rubber decomposition. The research investigates how rubber content, particle size, and decomposition kinetics influence structural integrity under fire exposure, aiming to balance sustainability (waste tire reuse) with fire resistance thresholds. Experimental validation included ISO 834 fire tests, thermogravimetric analysis (TGA), and compressive strength measurements on RMC specimens (0–30% rubber replacement). Parametric studies evaluated thermal conductivity, porosity evolution, and interfacial stress development across 20–1000 °C. Rubber content exceeding 20% accelerated porosity growth (28% at 600 °C), causing 55% compressive strength loss. Smaller rubber particles (1–3 mm) delayed decomposition but exacerbated interfacial cracking due to thermal expansion mismatch. The model demonstrated high predictive accuracy, with temperature and stress RMSD < 10% and R² > 0.94. Optimal performance was achieved at 10–15% rubber replacement, limiting strength loss to ≤ 40% at 600 °C while repurposing 130–195 kg/m³ of waste tires. The validated framework provides actionable guidelines for fire-safe RMC design, emphasizing ≤ 15% rubber content and 1–3 mm particles for structural elements. Results advocate code updates to address rubber-specific degradation, enabling sustainable construction aligned with UN SDGs. This work resolves bidirectional thermo-mechanical coupling in RMC—unachieved in Ozbakkaloglu et al.’s (2017) uncoupled model—reducing failure time errors from ± 25 to ± 8% while enabling fire-safe repurposing of 130–195 kg/m³ waste tires at 10–15% rubber content.

The external confinement of concrete columns using Fiber Reinforced Polymer (FRP) and Steel Reinforced Polymer (SRP) systems has emerged as a highly effective retrofitting technique for improving structural performance. This paper introduces newly developed predictive and design models for the compressive strength and ultimate strain of concrete confined with SRP, Carbon FRP (CFRP), and Glass FRP (GFRP). Making use of extensive experimental datasets, robust predictive equations are derived, and design equations are formulated using the “design assisted by testing” methodology outlined in Annex D of Eurocode 0 (EN 1990:2023), ensuring reliability and accuracy. The study highlights key differences in confinement mechanisms and failure modes across materials, with newly calibrated design equations offering practical applicability for a wide range of structural retrofitting scenarios. A comparative optimization analysis is also presented, evaluating the cost-effectiveness of SRP, CFRP, and GFRP systems for both strength enhancement and strain increment. This analysis provides engineers with actionable insights for selecting the most suitable material based on performance requirements and budget constraints. The findings represent a significant advancement toward unified, reliable, and economically viable design equations for enhancing the strength and ductility of reinforced concrete elements. This work promotes the broader adoption of SRP, CFRP, and GFRP systems by providing economically viable and reliable tools for practice.

As concrete chloride assessment methodologies are expensive and time-consuming, tests based on concrete resistivity have emerged as a cheap and quick solution. The formation factor has recently appeared as an alternative to evaluate the transport related properties of concrete. The formation factor is a physical property representing the ratio of the concrete's pore solution electrical conductivity to the material's electrical conductivity. In this study, from data published by RILEM, who collected experimental data from related literature, some of the key parameters of the pore solution have been analyzed. Results showed the statistical analysis of the experimental pore solution evolution for ionic species, some models proposed for the ionic concentrations and the evolution of the electrical conductivity. Additionally, models from the cement composition were obtained to predict the pore solution concentration. Finally, results of simulations using the NIST platform “Estimation of Pore Solution Conductivity” were compared to the experimental data available, finding a very good precision and accuracy of the model; however, some adjustment factors were proposed here to improve its accuracy.

The phase assemblage evolution of binders with novel supplementary cementitious materials (SCM_S) during exposure to adverse environments needs to be quantified to accelerate their adoption, and further optimize binder formulation. As such, the interaction between chloride and cementitious matrices with novel SCMs needs to be quantified. The goal of workgroup 2 of RILEM TC EBD-298 is to assess the methods used to quantify chloride binding. This state-of-the-art report reviews the standardized and novel methods to measure chloride binding through an average content (acid/water soluble) or a specific bound content per phase (XRD, TGA, SEM–EDS, …). Each method is presented with respect to our current understanding of chloride binding and speciation in cementitious materials. The discussion around the purpose, use and reporting of each method highlights the gaps limiting the comparison between studies, in particular the lack of standard protocol, and complementary characterization. This review is the groundwork for a “cookbook” of experimental workflows to investigate chloride binding in modern cementitious binders.

An innovative steel reinforced concrete frame with replaceable high damping concrete wall (SRC-HDCW) is proposed. The HDCW contains a polyvinyl alcohol fiber-reinforced rubber concrete wall panel and ten fuses made by low yielding point (LYP) steel. Two SRC-HDCWs are designed for the quasi-static cyclic test, in which the one is directly loaded to overall failure to verify its seismic performance. The other one is repaired by installing a new set of HDCW when it reaches the limit value of elastic–plastic story drift. The earthquake-resilient behavior is demonstrated through the rehabilitation in bearing capacity and stiffness. The failure mode, yielding pattern, hysteretic characteristics and ductility are analyzed. According to the features of obtained skeleton curve and hysteretic loop, a restoring force model based on quadri-linear skeleton curve as well as the corresponding hysteretic rule is proposed. The shear capacity and the initial stiffness of this hybrid structure are deduced. The relationship between initial stiffness and its degeneration at loading (unloading) path is fitted, in which the pinching behavior is considered. The predicted hysteretic curves are found to agree closely with those of the experimental specimens.

Rutting is a severe distress that significantly compromises the durability and service life of asphalt pavements. To clarify the creep failure mechanism of bitumen and enable accurate and practical failure time prediction, this study investigated the influence of viscoplastic deformation on the rutting performance and failure behavior of bitumen through long-term creep tests. For the first time, an Eyring’s activated flow model was applied in conjunction with the time–temperature superposition principle to accurately characterize the viscoplastic flow behavior of bitumen. A novel rutting failure criterion based on the unrecoverable deformation observed in the creep and recovery test was proposed to predict the rutting failure of bitumen under varying stress and temperature conditions in long-term creep tests. The consistent relationship between the plastic creep rate and failure time observed in both bitumen across varying temperatures indicates that the rutting failure is predominantly governed by a plasticity-controlled mechanism. Eyring’s activated flow rule effectively captures the evolution of viscoplastic flow in bitumen under varying stress and temperature conditions, while the time–temperature superposition principle proves effective in developing master curves across a wide temperature range. The proposed failure criterion demonstrates high accuracy in predicting the failure time of long-term creep tests. Moreover, the parameters governing bitumen failure were found to be insensitive to temperature variations. This study provides a robust foundation for developing predictive tools that remain reliable under diverse environmental conditions.

Many studies have employed the Alternate Load Path method to investigate the progressive collapse of building structures, yet they often neglect the influence of blast loads, which leads to inaccurate predictions of buildings structures progressive collapse mechanism. In this paper, a comparative experimental analysis was conducted on six reinforced concrete substructures subjected to explosion loads and one ALP-designed benchmark structure to examine their progressive collapse mechanism. The results indicated that the column-end force–time curves of the rubber test device exhibited higher peak forces with shorter durations, whereas those of the airbag test device showed lower peak forces but longer durations. The initial blast-induced damage in the substructures significantly reduced their rotational resistance capacity and accelerated the premature fracture of longitudinal reinforcements at beam ends. Consequently, the blast-damaged substructures exhibited a worse ductility performance compared with the benchmark structure. Moreover, during static pushdown loading, the vertical deformation profile of the benchmark substructure evolved from a double-curved shape to a straight line, while the blast-damaged substructures deformed primarily in a straight-line mode from the outset due to initial blast damage. These findings might provide valuable experimental evidence and design insights for enhancing the blast resistance design and progressive collapse analysis of building structures.

To address the anchor challenges of CFRP tendons used as cables, this study investigates the fatigue performance of a bonded CFRP tendon anchor system employing a three-segment anchorage design. Fatigue tests were conducted under a maximum stress of 0.5 (f_{u}) and stress ranges between 500 and 800 MPa. The fatigue failure mechanism was analyzed based on the bond–slip behavior between the CFRP tendon and the bonding medium. The effects of cyclic loading on tendon and sleeve stress, bond stress evolution in the anchor zone, and tendon stiffness were also evaluated. The results indicate that the anchor system withstood 2 million cycles under a 500 MPa stress range at 0.5 (f_{u}) maximum stress. Fatigue life was influenced by the stress range, with failure modes shifting from tendon splitting to tendon slippage as the stress range increases. Tendon axial strain progressively decreased and then stabilized with loading cycles, accompanied by a 22% increase in axial stiffness after 2 million cycles. The steel sleeve exhibited a slight increase in axial strain under cyclic loading, though the associated stress levels and amplitudes remained low. Within the anchor zone, bond stress and its amplitude were highest near the loading end, and bond stress within the tensioning end anchorage exceeded that in the fixed end. Fatigue failure initiated at the bonded interface near the loading end and propagated toward the free end, ultimately leading to global tendon slippage. Based on the fitted S–N curve, a stress range below 365 MPa is recommended for the three-segment anchor system with a fatigue lifespan exceeding 100 million cycles.