Materials and Structures最新文献

The aging of bituminous binders is a complex process that is influenced by a number of environmental factors including temperature, sunlight, humidity and reactive oxygen species (ROS) found in the troposphere. The effect of two of these factors, humidity and reactive oxygen species (ROS), are investigated in an environmental aging setup called the Viennese Binder Aging (VBA) method. Three unmodified and one polymer modified binder (PmB) were aged under conditions of varying duration (2 and 3 days), water exposure modes (direct versus indirect) and humidity levels. Additionally, experiments were conducted without the incorporation of ROS. Fourier transform infrared (FTIR) spectroscopy and Dynamic Shear Rheometer (DSR) were used for analysis. One binder showed accelerated aging due to the combination of ROS and humidity. Furthermore, a marginal increase in polybutadiene degradation due to humidity was detectable. However, when ROS were removed from the test setup, increasing the humidity levels did not increase the aging of any of the binders. The fact that the synergistic effects of humidity and ROS only affected the aging of one of the binders shows the complexity of this matter and highlights the importance of incorporating environmental factors into laboratory aging.

In this study, 3D numerical models for fresh concrete are established based on computational fluid dynamics (CFD) and discrete element method (DEM), respectively, and the comparative analysis is conducted to explore their advantages and characteristics in simulating the flowability of fresh concrete. To validate the reliability of proposed models, the simulated results are compared with experimental data obtained from this paper and other literature. According to the applicability of each numerical method, the influence of rheological parameters and coarse aggregate properties on the flowability of fresh concrete is further investigated. The findings indicate that both CFD and DEM models are capable of accurately predicting the flowability of fresh concrete, as evidenced by the strong correlation between the simulated and experimental results. The CFD model provides valuable insights into the rheological mechanisms governing the flow behavior of fresh concrete, while the DEM model excels at capturing the influence of constituent material properties. Within the specified ranges of yield stress (200–350 Pa) and plastic viscosity (30–60 Pa·s), an increase in the rheological parameters of the concrete mixture results in a decrease in both slump and slump flow. The relationship between coarse aggregate particle size and flowability is found to be non-monotonic, with slump and slump flow initially increasing and then decreasing as the maximum particle size increases from 16 to 31.5 mm. Additionally, when the density of coarse aggregates increases from 2.3 to 2.9 g/cm³, both slump and slump flow exhibit an increasing trend.

Growing concerns about the environmental impact of modern construction materials, particularly concrete, have renewed interest in earth-based construction. While chemical binders like cement and lime are commonly used to improve strength and durability, they increase embodied energy and limit recyclability. As a promising sustainable alternative, Enzyme-Induced Calcite Precipitation (EICP) enhances mechanical performance through calcium carbonate precipitation. However, its application to fine-grained soils remains limited, particularly regarding the influence of curing conditions and environmental factors on performance. This study explores EICP stabilization of compacted raw earth using soybean-derived urease in juice (SJ) and fine powder (SP) form, focusing on the effects of curing temperature (25 °C, 40 °C and 60 °C) and relative humidity RH (30%, 50% and 90%) on the mechanical performance and durability against water erosion. Results show that highest strength is reached at 25 °C and at 60 °C for SP and SJ stabilized samples, respectively. SP-stabilized samples showed no erosion in drip tests under all conditions except at RH = 90%, where erosion depth reached 2.88 mm. SJ samples instead were less erosive when cured at 60 °C, with an erosion depth of 3.35 mm. Results finally showed that drier samples (equalized at RH = 30%) are stronger and stiffer for both SJ and SP stabilizations. These findings underscore the critical role of curing conditions—specifically temperature and relative humidity—in the efficiency of EICP stabilization. They also demonstrate that the suction concept, widely accepted for unsaturated soils, remains applicable to EICP-stabilized soils, which are engineered materials incorporating calcium carbonate crystals and soybean-derived organic matter.

The demand for sustainable, energy-efficient buildings has accelerated the development of eco-efficient materials such as earth-based mortars (EBMs) reinforced with plant-based additives. This study investigates the impact of incorporating bamboo particles (0, 3, 6, and 9 vol%) on the hygrothermal, mechanical, and environmental performance of EBMs intended for interior wall render/plaster (non-structural). Bamboo particles were characterized by water absorption, bulk density, scanning electron microscopy (SEM), and moisture buffer value (MBV). The mortars were evaluated using mercury intrusion porosimetry (MIP), MBV, water vapor permeability (WVP), thermal conductivity, bulk density, compressive and flexural strength, post-peak toughness, and a cradle-to-site life cycle assessment (LCA; A1–A4) with eco-efficiency indicators. Bamboo addition decreased bulk density (up to ≈ 14%) and thermal conductivity (up to ≈ 30%), while enhanced MBV (up to ≈ 41%) and WVP generally increased within the tested range, and MIP/SEM indicated a more open pore network and modified interfacial bonding. Capillary absorption and drying index increased, indicating greater porosity and improved vapor diffusion. At higher bamboo contents, compressive strength was reduced, whereas post-peak toughness and crack resistance improved, with clear post-peak gains. LCA results were largely driven by hydrated lime and cement, while biogenic carbon associated with bamboo partially offset climate burdens. Overall, eco-efficiency improved on hygrothermal axes with application-dependent trade-offs on mechanical performance, consistent with the non-structural nature of interior plasters. These results highlight the potential of bamboo-reinforced earth mortars as low-carbon, moisture-regulating materials for interior application and climate-resilient building. The scientific contribution lies in combining microstructural evidence (MIP/SEM), multi-domain performance tests and LCA into quantitative eco-efficiency indicators, with explicit consideration of biogenic carbon to quantify carbon-performance trade-offs of bamboo in EBMs.

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To promote the sustainability of magnesium oxychloride cement (MOC) in construction applications, this study proposes a biomass-based modification strategy to optimize its rheological performance. Biomass bottom ash (BBA) and tannic acid (TA) were employed as eco-friendly additives, and their synergistic effects on MOC’s early-age properties were systematically investigated via rotational rheometry, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TG). The results show that BBA reduces plastic viscosity by physically diluting reactive phases, while its irregular morphology induces dynamic particle jamming at high shear rates, leading to shear thickening. Meanwhile, TA reduces the yield stress of MOC paste through electrostatic repulsion from its phenolic hydroxyl groups. The synergistic interaction between BBA and TA forms a "gel-wrapped particle-filling" structure. While this does not prevent the intrinsic shear-thickening at high shear rates, it modifies the paste’s initial structure, thereby improving its overall workability. Although the addition of BBA and TA leads to a reduction in 1d compressive strength due to decreased ({hbox {5MgO}}cdot hbox {MgCl}_{hbox {2}}cdot hbox {8H}_{hbox {2}}{hbox {O}}) crystals (phase 5) formation, this modification strategy effectively extends the workability window of MOC. This study offers a sustainable approach to enhance the constructability of MOC and promotes the large-scale utilization of biomass waste in green cementitious materials.

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.