Materials and Structures最新文献

This paper presents the results of experimental investigations on six-layered, homogeneous glulam beams made of Italian short supply chain beech (Fagus sylvatica L.). At first, the beams were produced and mechanically characterized for bending, then, they were employed to realize timber-timber composite joints and tested under quasi-static monotonic loading. The test configurations were adopted to reproduce connections used in timber-to-timber composite structures for applications in new constructions. Outcomes in terms of connection stiffness, strength, static ductility and failure modes are presented and discussed. Moreover, the experimental stiffness were used to carry out analytical verification at the serviceability and ultimate limit states to extend the validity of the proposed screw and specimen’s configurations.

Demographic growth and the need for housing remain significant issues. Compressed earth bricks (CEB) are appropriate materials due to their availability and thermal properties, but different considerations hinder their adoption. The influence of water on the mechanical properties and durability of CEBs stabilised with an alkali-activated geopolymer binder has yet to be thoroughly investigated. Thus, this study assessed the hydromechanical performance and durability of compressed earth bricks (CEBs) stabilised with an alkali-activated geopolymer binder. Dry mixes consisting of lateritic earth and 5—20% metakaolin (MK) binder, with respect to the dry mass of the earth, were prepared. A solution of NaOH at a concentration of 12 M was used to activate MK. The wet mixes were then statically compressed using a manual press at a stress of about 3.5 MPa. The dried CEBs were subjected to progressive mechanical characterisation after exposure to different water content and durability indicators assessment. A satisfactory mathematical correlation was established between the relative compressive strength and water content of the CEBs. CEBs stabilised with geopolymer binder showed increased stability to water, and their absorption capacity was relatively below the recommended 20% threshold. The abrasion resistance coefficient improved after the wetting–drying (W-D) cycles and was above the recommended 7 cm²/g.

The mechanical response and fracture behavior of two architected 3D-printed hardened cement paste (hcp) elements, ‘lamellar’ and ‘Bouligand’, were investigated under uniaxial compression. A lab-based X-ray microscope was used to characterize the post-fracture crack pattern. The mechanical properties and crack patterns were analyzed and compared to cast hcp. The role of materials architecture and 3D-printing-induced weak interfaces on the mechanical properties and fracture behavior are discussed. The pore architecture that inadvertently forms in the design of solid architected materials dictated the overall mechanical response and fracture behaviors in both 3D-printed architected materials. While no specific crack pattern or microcracking was observed in the cast element, lamellar architecture demonstrated a crack pattern following weak vertical interfaces. Bouligand architectures, on the other hand, exhibited a helical crack pattern with distributed interfacial microcracking aligned with the helical orientation of filaments. As a result, the bouligand architected elements showed a significant 40% increase in work-of-failure compared to cast counterparts. The enhanced energy absorption was obtained without sacrificing the strength and was attributed to higher fractured surface and microcracking, both of which follow the weak helical interfaces.

In the production of asphalt mixtures containing reclaimed asphalt pavement (RAP), the traditional heating method has certain limitations, such as partial mobilization, low blending, and secondary aging. These drawbacks result in reduced technical properties of recycled asphalt mixtures, such as the crack resistance, fatigue resistance, and water stability, thereby leading to strict restrictions of RAP content in the recycled asphalt mixtures. To address these issues, microwave induction was used in this study to produce recycled asphalt mixtures. Fluorescence microscopy and molecular dynamics simulation with thermoelectric coupling field were used to examine the viability of increasing the blending efficiency by adding nanometer microwave absorbents. The findings show that microwave induction can be used to increase the blending efficiency of aged and virgin binders and that adding nanoscale microwave absorbents can further increase this efficiency. By incorporating nanoscale SiC at a concentration of 0.5%, the temperature-rising rate of asphalt under microwave heating was improved by up to 31.4%. The self-diffusion coefficient of asphalt incorporating microwave absorbent is dramatically raised and is 2.1 times that of virgin asphalt without microwave absorbent and 4.9 times that of aged asphalt, indicating that microwave absorbent is conducive to the blending of virgin and aged asphalt under microwave action.

Asphalt, a widely utilized binder material in pavement construction, brings notable environmental and economic advantages through its efficient and high-utilization technique of multiple recycling. Nevertheless, the microscale mechanical mechanisms and laws governing the damage evolution in asphalt during repeated aging and recycling processes remain unclear, posing challenges in determining the optimal reclamation method and timing for binder maintenance. This study seeks to bridge this gap by employing microstructural numerical simulation and viscoelastic computational methods to elucidate the fundamental changes in microstructural mechanics and relaxation spectra of asphalt binders during multiple aging and regeneration processes, ultimately enhancing the design efficiency of multiple regeneration pavements. The study’s key findings revealed that aging decelerates the relaxation capacity and increases the modulus of asphalt, while regeneration reduces the modulus and enhances relaxation capacity. The initial two aging and regeneration processes significantly influenced the stress distribution in the microscopic phase of the asphalt. Following the third aging and rejuvenation, the stress threshold and area of stress concentration remained relatively unchanged. Aging and regeneration primarily alter the mechanical properties of the microscopic phase, affecting the stress relaxation capacity and complex modulus of asphalt. The present study provides a certain research basis for the micro-mechanism of multiple regeneration asphalt.

Based on the strain reduction coefficient methodology, which enables an analysis of a beam with external or internal unbonded tendons as a beam with bonded tendons, and using the age-adjusted effective modulus method for time analyses of prestressed concrete members under long-term loads, this paper proposes an equation for the calculation of prestress loss in simply supported beams with internal unbonded tendons. The proposed equation takes into account the effects of concrete creep, concrete shrinkage, relaxation of the prestressing steel, and the presence of a bonded, non-prestressed reinforcement. The main goal of this study is to reduce a relatively complex problem, in which it is necessary to analyse the member as a whole, to one of sectional analysis. As our main conclusion, we find that the loss of prestress obtained by applying the proposed equation has an accuracy that is comparable with the results of previous studies and with the application of existing formulations.

A straightforward mixing approach that involves incorporating glass fiber into cement-based materials is frequently carried out at construction sites. This practice can have adverse effects on both the fresh and hardened properties of cement mixtures. The lack of quality control measures often leads to the production of fiber-reinforced cement mixtures that do not perform as intended. Additionally, the inherent variations in commercially available glass fibers of the same type add complexity to mixing, making it difficult to consistently reproduce desired effects for in situ casting. Therefore, this research aims to accomplish three main objectives. Firstly, characterizing E-glass and AR-glass fibers to enable a practical replication of performance using these specific variants. Secondly, assessing the impact of five different mixing methods on water absorption, flowability, setting time, compressive, and flexural strength in cement mixtures embedded with these glass fibers. Lastly, evaluating the fiber-matrix interaction within the hardened samples for each mixing method. The results revealed that various mixing methods yielded distinct advantages in the fresh and hardened properties. This highlights the variability in mixing approaches, indicating that the choice of method should be tailored to meet the specific construction requirements of engineers. In essence, the study underscores the importance of selecting an appropriate mixing technique based on the desired outcomes for both the fresh and hardened states of cement mixtures.

The utilization of engineered wood products is becoming more and more important when it comes to carbon sequestration and sustainable building. Among them, Cross-laminated timber (CLT) has emerged as a popular mass timber product, offering enhanced structural properties and environmental benefits. This study investigates the potential of incorporating small-diameter trees as corrugated wood-strand composite panels into CLT, developing a cellular cross-laminated timber (CCLT). A systematic investigation was carried out to assess the impact of core geometry on the flexural stiffness of CCLT panels utilizing the finite element method. Six cases involving combinations of fixed and variable geometrical parameters were examined to determine the effect of each geometrical parameter. The findings revealed a substantial positive effect of corrugation depth, while bond length and unit cell length exhibited a negative influence on bending stiffness. Other geometric characteristics play a minor, supportive role. Considering the insights derived from the parametric study and considering manufacturing constraints, a corrugated geometry was designed and fabricated using an aluminum matched-die mold. The CCLT panels, constructed using these corrugated panels, were evaluated against predictions from a finite element model, demonstrating close agreement. Moreover, the CCLT exhibited a higher value of normalized modulus of elasticity by density compared to conventional CLT.

This study introduces a novel non-prestressed concrete precast bottom slab with a section steel and two ribs, designated as NPBS2R. The research aimed to evaluate the effect of section steel form and steel trusses on the flexural performance of NPBS2R. A comprehensive analysis, including three-point static loading tests and numerical simulations, was conducted on five full-scale specimens. The findings reveal that all NPBS2R specimens satisfy the free support construction requirements. Compared to conventional non-prestressed precast bottom slabs with steel trusses (NPB), the NPBS2R’s cracking moment improved by 43.5–59.5%. The section steel, remaining unyielded in tests, demonstrates potential for reuse, with its form exerting minimal impact on the overall flexural stiffness of NPBS2R. The presence of steel trusses was observed to marginally enhance the flexural behavior, contributing to a 15.0% increase. The numerical study highlights that the section size of the section steel, the chord diameter of the steel truss, and the truss quantity significantly influence NPBS2R’s flexural performance. The theoretical values derived from the study closely align with the experimental and numerical outcomes, confirming the established calculation formula’s accuracy and reliability for practical engineering applications.