Materials and Structures最新文献

The opening of mortises in wooden components has a significant impact on their load-bearing performance. To investigate the impact of mortises in timber columns of timber structures on their bearing performance, a study was conducted utilizing static loading tests on timber columns featuring mortises. The findings indicate that employing solid wood square materials produced by modern industry for the columns of the timber structure effectively addresses common limitations associated with traditional log columns, such as high moisture content, low processing precision, significant taper, and susceptibility to deformation and cracking. The mortise width to column width is a critical determinant of the effective bearing area of the timber column and significantly influences its bearing capacity. Specifically, an increase in the mortise width to column width correlates with a decrease in the bearing capacity of the timber column. In comparison to intact timber columns, the ultimate bearing capacities of timber columns with mortise width to column width of 1/4, 1/3, and 1/2 are reduced by 10.76%, 17.92%, and 40.95%, respectively. Additionally, as the slenderness ratio of the timber column with a mortise increases, its bearing capacity diminishes, and the failure mode transitions from strength failure of the wood near the mortise to compression-bending instability failure. The Digital Image Correlation (DIC) strain nephogram reveals that high-stress areas initially develop at the corners of the mortise, which serves as a critical factor contributing to the bearing instability of the mortised timber column. Both cross-shaped and offset-shaped mortises inflict considerable damage on the timber column, resulting in reductions in bearing capacities of 48.96% and 37.76%, respectively, compared to intact timber columns.

Traditional cement-based grouting materials exhibit inadequate toughness, poor interfacial bonding performance, and limited durability, which restrict their application in engineering structures such as tunnels. This study systematically investigates the enhancement mechanisms and interfacial reinforcement effects of waterborne epoxy resin (WER) on the performance of calcium sulfoaluminate grouting materials (WECG) by integrating experimental investigations with molecular dynamics simulations. The primary focus is on analyzing the influences of WER dosage and the water-to-cement ratio (W/C) on the setting time, water bleeding, fluidity, and mechanical properties of the grout. The results indicate that the incorporation of WER significantly improves the flexural and compressive strengths of WECG, with maximum increases of 34.8 and 33%, respectively, while effectively reducing water bleeding and delaying the setting time. Microstructural analysis demonstrates that WER forms an interpenetrating network structure with hydration products, thereby enhancing interfacial bonding and increasing matrix density. Molecular dynamics (MD) simulations at the atomic scale elucidate the “bridging” role of calcium ions at the interface between ettringite and WER through Ca–O coordination bonds, clarifying the micro-mechanisms of interface reinforcement.

Fatigue resistance performance has always been a key focus of research on recycled asphalt mixtures, as it is crucial for the long-term road performance during actual service. This study aims to propose a systematic structural design method for recycled asphalt pavement. Specifically, the dynamic modulus and fatigue tests are conducted to investigate the tension-compression anisotropy of recycled asphalt mixtures. A viscoelastic continuum damage model is employed to analyze the effects of layer thickness, axle load, and recycled asphalt pavement (RAP) content on the evolution of fatigue damage. To further guide structural design, a fatigue life equivalence method is introduced. The results reveal that the ranking of fatigue life for mixtures with varying RAP contents exhibits an inverse trend between tensile and compressive directions. The standard fatigue damage curve is established by analyzing the evolution of pseudo-stiffness throughout the fatigue cycle. Based on the principle of fatigue life equivalence between recycled and newly constructed structural layers, adjustments to the recycled layer thickness and RAP content are proposed to satisfy the fatigue life requirements of newly built asphalt pavements. Finally, an extrapolation method requiring minimal computational data is introduced to predict fatigue life, and its effectiveness is verified. This study provides a robust framework for the structural design of recycled asphalt pavements, offering practical guidance for enhancing pavement performance and sustainability.

Reusing reinforced concrete structures within a Circular Economy offers substantial environmental benefits, but requires reliable assessment of their remaining service life. Conventional approaches to concrete durability, based on prescriptive design parameters for new structures or carbonation depth measurements in existing ones, are insufficient to ensure reuse for an additional 50 or 100 years. This study addresses this gap by introducing a performance-based probabilistic framework for evaluating carbonation‑induced corrosion, tailored to circular construction. The study incorporates parametric analysis and probabilistic modeling of corrosion initiation and propagation phases, and assesses two precast concrete buildings located in Nordic climates. The study also examines how storage period before reuse, changes in exposure class after deconstruction, altered carbonation rates during a second service life, and repair interventions, affect service life. Monte Carlo simulations are used to estimate the total service life under various conditions, with outdoor carbonation rates reflecting typical Nordic exposures. Corrosion propagation is modelled following fib Model Code 2020 and fib Bulletin 112. The results demonstrate that reused concrete elements can achieve service lives comparable to new structures, provided that performance-based assessment and appropriate repair interventions are applied. The proposed framework supports data-driven decisions on service life, repair, and reuse strategies for structural concrete, considering exposure classes and performance. It can be complemented by non-destructive testing and durability indicators. It provides a scientific basis for extending the service life of reused concrete elements and supports design for circularity and resource efficiency, thereby advancing circular construction and the transition toward a sustainable built environment.

Timber railway bridges are an important aspect of Canada’s heritage. In this study, the mechanical properties of 12 decommissioned creosote-treated Douglas fir beams from a railway bridge were investigated. Longitudinal and transverse stress-wave analysis, vibration testing, resistance drilling, and destructive testing were employed. Resistance drilling identified localized density variations but showed no direct correlation with global density. The stress-wave analysis yielded an average modulus of elasticity ((E_{sw})) of 15,090 MPa, and vibration testing yielded a dynamic apparent MOE ((E_{app,v})) of 12,102 MPa and a true MOE ((E_{true,v})) of 17,046 MPa. Finally, destructive bending tests produced static MOE values ranging from 8,564 MPa to 11,722 MPa. The beams exhibited failure primarily in shear, at an average maximum shear stress of 3.7 MPa and an average maximum bending stress of 29.6 MPa. Two beams were subjected to fatigue testing: one beam endured 80,000 loading cycles without degradation, while the second exhibited shear failure after 28,000 cycles. The findings emphasize the complexity of accurately assessing the mechanical properties of timber using non-destructive methods in the conservation of historical timber structures.

Steel fibre reinforced concrete (SFRC) offers better performance for pavements and industrial floors. However, its adoption in pavement is still limited due to lack of experimentally validated fatigue-based design methods. This study experimentally investigates the fatigue response of pre-cracked SFRC slabs at four stress levels under load control. Slabs were pre-cracked to 95% post-peak load drop, and cyclic loading continued until one million cycles, 10 mm deflection, or failure of the specimen whichever occurs first. Results show significant enhancement in both load-carrying capacity and rotation capacity with increased fibre dosage (0.3% to 0.4% V_f). Theoretical fatigue response, estimated using yield line analysis and material models, aligned conservatively with experimental findings. A generalized fatigue model (GenFRC), integrated into a mechanistic-empirical design approach (MEFRC), provided optimized thickness for SFRC pavements. The study validates fatigue-based design for SFRC pavements and supports broader adoption through experimentally backed models.

This study evaluates the viscoelastic behavior of asphalt concrete incorporating Sintered Aggregate of Calcined Clay (SACC) through a comparative analysis of the Huet-Sayegh, 2S2P1D, and GHS models. The 2S2P1D model was identified as the most parametrically efficient, a finding supported by the GHS model, which showed that a third parabolic element was superfluous. The primary contribution lies in the interpretation of the fitted parameters, which defines a unique rheological signature for the SACC mixture: a lower glassy modulus coupled with an exceptionally high resistance to permanent deformation. This advantageous performance profile, particularly suited for high-temperature applications, shifts the focus from simply advocating for SACC use to providing a fundamental, model-based rationale for its implementation in sustainable pavement design.

Optimizing the utilization of SCMs in concrete requires understanding their composition-structure–reactivity relationships, a task that remains challenging due to their inherent structural and chemical complexity. This study addresses this challenge by analyzing a diverse range of calcium aluminosilicate (CAS) glasses, serving as pure-phase model systems to better understand SCM reactivity. Sixteen CAS glasses were synthesized, with their amorphous nature confirmed by X-ray diffraction (XRD), and their reactivity assessed using heat release measurements from a modified R³ test. X-ray diffraction (XRD) was performed to study the glass structure. Although several structural parameters—non-bridging per tetrahedral oxygens (NBO/T), average Qⁿ (Si) species, metal–oxygen bond strength (S_M–O), the average number of topological constraints per atom (n_r), and XRD hump maxima angle—correlated linearly with CaO (reflecting its depolymerizing effect), the 72-h heat release followed a non-linear trend with CaO. It increased initially, peaked at around 35–45 mol % CaO, then decreased. Consequently, high-CaO glasses reacted rapidly but did not sustain their reaction over time, whereas those with higher SiO₂ content showed slower yet more prolonged reactivity. These findings demonstrate that reactivity cannot be directly predicted from existing structural descriptors alone.

This study focuses on the use of seashell wastes as sand on the design of pervious concrete paving blocks by combining alkali activation and vibro-compaction. This work integrates three sustainability levers simultaneously: (i) the valorisation of seashell wastes as a complete replacement for natural sand, (ii) the synergistic use of fly ash and coal mining tailings as alkali-activated precursors, and (iii) the application of accelerated carbonation as a curing strategy for strength enhancement and CO₂ capture. Results reveal that carbonated paving blocks with 100% seashell sand exhibited remarkable performance gains, with compressive and splitting tensile strengths improved by 27% and 60%, respectively, compared to uncarbonated mixes. Moreover, splitting strength values at only 3 and 7 days of carbonation surpassed the EN 1338 standard threshold (2.5 MPa), underscoring the rapid development of mechanical performance. Beyond mechanical enhancement, carbonation curing also improved abrasion and skid resistance. This research makes a significant contribution to the field of sustainable pavements, creating new prospects for circular economy approaches that integrate marine waste recycling with carbon capture.

Most studies on the fatigue performance of cement concrete pavements overlook the different mechanical characteristics between tension and compression and complex service conditions. This limits the accuracy of durability evaluation. To address this issue, this study investigated four-point bending fatigue tests considering tension–compression differences. The decay patterns of tensile and compressive moduli were revealed. A numerical model was developed, incorporating coupled tensile–compressive stress fields and temperature fields in the cement pavement structure. The evolution of structural responses was analyzed. Results showed that the four-point bending fatigue life before and after considering tension–compression differences differ by more than 90%. A correlation between the two conditions was established. The moduli decay rates followed a power-law relationship with stress level. A unified fatigue decay model for tensile and compressive moduli was established. The decay rate of tensile modulus was higher than compressive modulus. At failure, the ratio of compressive to tensile modulus was up to 3.5 times the initial stage. The tensile modulus decay was the key dominant factor in fatigue failure. Mechanical response varied as power functions with axle load cycles. The maximum tensile stress at the base layer bottom increased over 140%. When axle load cycles exceeded two-thirds of total design life, the surface layer lost more than 75% of service life, and the base layer began to decay rapidly. This revealed the evolution mechanism of structural stress: “surface deterioration—base takeover—structural instability”. The findings provide a basis for durability design of cement concrete pavements under complex service conditions.