Materials and Structures最新文献

The finite element simulation of multi-crack propagation in asphalt mixture typically involves the use of a global stiffness matrix, which poses significant memory demands. To address this limitation, this study developed a pixel-based finite element method (PFEM) for simulating multi-crack propagation in asphalt mixtures, which effectively eliminates the need for a global stiffness matrix, thereby reducing memory usage by 51.5%. In PFEM, each pixel of asphalt mixture computed tomography (CT) image is treated as an individual finite element, with an embedded boundary element technique used to mitigate stress concentrations along jagged boundaries of asphalt mixture components, and the maximum tensile stress adopted as the failure criterion for the pixel-based finite elements. The crack path simulated by PFEM for asphalt mixtures are closed align with those obtained using a peridynamic numerical model, verifying the accuracy of PFEM method. The simulation results reveal that stress concentration near the voids triggers crack initiation in fine aggregate mixture. As cracks propagate, they may deflect or connect with the air voids, and the stress concentrations among multi-crack tips further promote crack coalescence. This work not only provides a novel method for calculating multi-crack propagation in asphalt mixture, but also opens new avenues for studying the pixel-level cracking behavior of asphalt mixtures.

Sustainable construction requires advanced materials that minimize environmental damage. This research explores the interaction among fine glass powder (FGP), coarse glass powder (CGP), silica slurry (SS), and polyolefin fibers (PF) in self-compacting concrete (SCC). The optimum combination (15% FGP, 5% SS, 1% PF) improved flow by 17% without reducing strength or causing segregation. Mechanical performance improved significantly: 45.24% enhanced compressive strength, 25.79% increased tensile strength at 28 days, and 80.75% increased flexural strength at 28 days. Durability testing showed 35.7% reduced sorptivity. The microstructure examination (SEM, XRD, stereo microscopy) confirmed a denser structure with fewer voids, increased C-S–H gel formation, and improved pore structure. PF improved post-cracking performance through microcrack bridging, while FGP and SS assisted in making the matrix denser. CGP offered an economic alternative with only a 4.76% loss in strength. The study establishes two sustainable approaches: a high-performance FGP solution and a cost-effective CGP alternative, advancing sustainable construction through effective waste utilization.

This paper introduces a simplified shear load-slip analytical model for evaluating shear transfer across monolithic uncracked (MU) interfaces, which was developed based on push-off tests and the proposed interface shear mechanism. The model formulates equations for four characteristic shear loads—cracking load (V_cr), ultimate shear capacity (V_u), residual shear capacity (V_r), and failure load (V_f)—along with their corresponding slip deformation. Fifteen push-off tests were conducted to assess the contribution of shear reinforcement throughout the shear resistant process, varying the shear reinforcement ratio, and the yield strength of shear reinforcement. Results from the push-off test and subsequent analysis of the interface shear mechanism indicate that V_cr is governed primarily by concrete properties, whereas V_u arises mainly from concrete cohesion and shear friction generated by the unyielded shear reinforcement, with concrete cohesion playing the dominant role. A comparative analysis demonstrates that the model’s prediction closely match the observed shear load-slip responses. Notably, the proposed V_u equation, incorporating the elastic modulus (rather than yield strength) of shear reinforcement, was systematically compared to existing design equations from the American Concrete Institute (ACI), the Precast/Prestressed Concrete Institute (PCI), Canadian Highway Bridge Design Code (CSA), and AASHTO LRFD Bridge Design Specifications, using a database of 135 MU interface push-off test results. The evaluation shows that the proposed equation offers significant advantages over existing equations, achieving an average experimental–to–nominal shear capacity ratio of 1.06 and a coefficient of variation of 0.17.

This study investigates the correlation between the structural parameters of coarse aggregates and the rheological properties of concrete based on the multifractal analysis method. The discrete element method was used to simulate and analyze the distribution attributes of coarse aggregates. Correlation indices were established between the slump, rheological parameters and multifractal parameters through experimental testing and numerical simulation. The results indicate that the gradation, shape, and size of coarse aggregates influence the rheological properties of concrete by altering the spatial distribution characteristics of the aggregate structure. The fractal dimension (D) and multifractal spectrum width (Delta alpha) show a negative correlation with slump and flow spread, but a positive correlation with yield stress and plastic viscosity. The multifractal spectrum width (Delta alpha) considers the heterogeneity in the spatial distribution of aggregates, enabling a more accurate prediction of concrete rheological behavior. This finding offers new insights for quantitatively analyzing the role of coarse aggregates in fresh concrete and for predicting its rheological behavior.

The climate crisis is driving an increasing demand for ecologically oriented concepts. In the building sector, this demand includes not only the use of environmentally friendly materials but also the greening of urban areas. One promising approach is the development of bioreceptive concrete façades, which support the growth of green biofilms directly on their surfaces. These innovative façades are anticipated to deliver benefits comparable to those of macroscopically greened façades, such as enhanced biodiversity and improved air quality, while offering the advantages of being more self-sustaining and stable systems once fully established.

However, the development of bioreceptive concrete presents substantial challenges. Due to the interdisciplinarity and novelty of this field, standardized methods for material characterization and bioreceptivity assessment are currently lacking. This study proposes an approach for evaluating surface properties crucial for bioreceptivity, developed on differently structured samples of ultra-high-performance concrete (UHPC). Existing methods and standards from concrete technology are critically reviewed and, where necessary, modified to meet the unique requirements of measuring bioreceptive material properties. Special attention is given to the surface pH value and water retention characteristics, as these are essential for promoting microbial growth and ensuring the long-term stability of green biofilms. The observed surface characteristics vary according to the imprinted surface structures, offering a spectrum of material properties and enabling the evaluation of their impact on bioreceptivity. The findings presented form the foundation for subsequent laboratory weathering experiments, which will be discussed in a complementary publication.

Due to their high specific surface, the incorporation of calcined clays (CC) as supplementary cementitious materials (SCMs) reduces the workability of standard mortars, as Water/Binder ratio (W/B) and compaction energy are kept constant, while assessing their activity according to NF EN 196-1. Thus, mortars incorporating calcined clays display a different initial porosity than reference mortars made with Ordinary Portland Cement (OPC). In this study, the impact of the variation of the initial porosity on compressive strength at 28 days and consequently on measured CC activity is first assessed. Two types of binder are here studied: 85wt% OPC + 15wt% CC and LC3-50 (limestone calcined clay cement with 50wt% clinker) with three different kaolinitic clays, calcined at different temperatures. A method is proposed to accurately measure the air fraction in the mortars to be able to compare compressive strength of these at similar porosity, allowing to get rid of experimental variation in porosity for binder activity assessment. It seems that evaluating the activity of a binder with Strength Activity Index (SAI), regardless initial porosity can lead to an underestimation of the activity of binders containing calcined clays.

The need of more sustainable structures pushes ahead the formulation of new advanced cementitious materials which can significantly improve the structural durability, thus resulting into a longer service life with reduced maintenance. Within this framework, the research project ReSHEALience (H2020 GA 760824) has developed a new approach for the design of structures exposed to extremely aggressive environments, starting from a novel concept of High-Performance Fiber-Reinforced Concrete (HPFRC). In a design perspective, this makes it necessary to effectively identify the main parameters describing the overall material behaviour in tension (this being instrumental also for the durability estimation in the cracked state). In the present study, starting from the results of 4-Point Bending Tests on small beams, an inverse-analysis identification procedure has been implemented in order to evaluate the response in direct tension in terms of stress–strain and stress-crack opening laws. The procedure has been implemented for three different HPFRC mixes differing in the type of fibre (straight steel or amorphous metallic ones) and of cement (CEM I or CEM III). The characterization procedure allowed to highlight the effect of fibre type on the whole response in direct tension in terms of loading–unloading response and post-peak regime. In this view, the study aims at further pushing forward the adoption of HPFRC in the design of structures, thanks also to the increasing awareness fostered by the most recent standards.

This article presents experimental results from fatigue tests in form of load-controlled cyclic tension-swelling, i.e. repeated tensile loads and alternating tension–compression on high-strength polyethylene-reinforced SHCC, subjected to a sinusoidal loading regime with a fixed upper load limit and variable lower stress levels, corresponding to zero, moderate and high compression depending on the load regime. To assess material degradation, crack development and opening were determined using DIC during the cyclic tests. Electron microscopy of the fracture surfaces reveal different load-dependent degrees of material deterioration. Together with the results from DIC, a stable basis for the discussion of the material’s performance under the employed loading regimes is provided. The analysis revealed a decrease of the maximum number of loading cycles with increasing compressive stress leading to a more severe deterioration of the material that is reflected in both the mechanical performance and crack development.

This study explores the structural performance of concrete cylinders confined with glass-based fabric-reinforced cementitious matrix (FRCM) systems, emphasizing the effects of prolonged exposure to alkali-rich environments. FRCM confinement has gained attention for its ability to enhance compressive strength and ductility in concrete elements, but its long-term durability under chemically aggressive conditions remains a critical concern. In practical applications, exposure to alkaline environments—such as those found in concrete pore solutions—can significantly impact the mechanical integrity of the composite system, particularly the bond between the glass fibers and the cementitious matrix, which is essential for effective confinement. To assess these effects, an experimental program was conducted involving glass-FRCM coupons, dry fabrics, and concrete cylinders externally wrapped with glass-FRCM. These specimens were immersed in a simulated alkaline solution for durations of 1000, 2000, and 3000 h. Both confined and unconfined cylinders were subjected to axial compression tests to evaluate changes in compressive strength, axial strain capacity, and failure mechanisms. Additionally, digital microscopy was used to examine microstructural deterioration and chemical alterations in the glass fibers and matrix, providing insight into the degradation processes at the fiber-matrix interface. The results indicate that alkali exposure progressively weakens the interfacial bond between the glass fibers and the cementitious matrix, with the extent of degradation closely linked to the exposed surface area. This deterioration leads to a measurable decline in confinement effectiveness over time.

Graphical Abstract

The present work investigates the effect of substituting natural coarse aggregates (NCA) with recycled coarse aggregates (RCA) obtained from multiple recycling cycles on the flexural creep of concrete beams under sustained bending loads. Four types of concrete with the same water-to-cement ratio were analyzed: natural aggregates concrete (NC) and three generations of recycled aggregate concrete, where NCA was replaced by RCA in each generation, with volume substitution of 50 and 100%. Creep coefficients and creep deformations velocity were assessed for all concretes In addition, the flexural creep strains of concretes are predicted using Burger’s rheological model, which is the most widely model used to describe the viscoelastic materials properties. The experimental results show that multi-recycling has a negative impact on the flexural creep of concrete. An increase in recycling cycles and RCA content results in higher compressive and tensile creep as well as in the creep coefficient and creep velocity, but using 50% RCA has a lesser impact on this deformation. Finally, the compressive and tensile creep strains predicted using Burger’s rheological model demonstrate good consistency with the experimental investigations results over the assumed range of multi-recycling cycles, RCA volume substitution, and measurement durations.