Materials and Structures最新文献

The inevitable snow accretion over pavement in winter is always troublesome for transportation systems. Many open questions on road icing and snowing remain, and there is significant demand to develop a green, reliable, efficient, and secure approach for ice and snow cleaning. This work fabrication of a mechanically tough, flexible, and highly conductive graphene-paper (GP). This novel material demonstrates a combination of mechanical robustness and high conductivity, making it suitable for self-heating applications. Based on the remarkable Joule heating effect of GPs, which served as efficient heating elements and was embedded into an emulsified asphalt pavement slab (APs) to construct a new type of self-heating system through a separately packaged and uniformly integrated procedure. Owning to the conductivity of the GPs reached up to 5300 S/m, thermal energy could be provided via clean energy (such as solar, wind, and tidal energy), contributing to the goal of carbon neutrality. Furthermore, the APs demonstrates ice melting under the extreme temperature condition of − 30°C without damaging the pavement structure. What’s more, the ability of anti-accretions of snow has resisted the extreme blizzard in unfavorable weather. Such self-heating pavement based on GPs has the advantages of high efficiency, good stability, and outstanding safety for both snow-melting and deicing.

Very-High-Performance Concrete (VHPC) are defined as concrete capable of reaching compressive strength higher than 80 MPa. These performances can be reached thanks to its compact and extremely dense microstructure, as a result of a proper mix. Together with their great durability properties, these concretes may lead to reduce cross sections of structural elements and thus save material and built volumes. The addition of synthetic fibers allows to significantly increase the toughness and crack opening resistance, beyond the tensile strength. These benefits can easily be traduced in an improved durability of the VHPC concrete. the aim of this research activity is to enlarge the experimental database of high-performances concrete reinforced with synthetic fibers having different size. In fact, contrary to the case of steel fibers, few works are report ed in literature regarding the types of fibers investigated herein. In the present work three Very High-Performance Fiber Reinforced Concrete (VHPFRC) mixes have been studied and characterized in laboratory. The mixes were realized with the same VHPC concrete matrix and different types of synthetic fibers: 10 mm straight polyvinyl alcohol (PVA) fibers; 30 mm waved polypropylene (PP) fibers; 40 mm waved polypropylene (PP) fibers. The first mix was realized using PVA fibers only, the second with 30 mm PP fibers and the last one was obtained by mixing PVA fibers and 40 mm PP fibers. A further VHPC mix with no fibers has been also realized and tested as reference material. Compression tests on both cylindrical and cubic specimens and modulus of elasticity tests have been performed for each mix. The VHPFRC toughness have been determined by means of three-points bending tests according to EN 14651. The bending parameters obtained from the experimental test have been compared between all the mixes and an analysis of the fracture energy has been performed. Moreover, each mix has been tested at bending with four-points setup in order to verify the efficiency of this test type for VHPC reinforced with synthetic fiber. The results provided in the paper highlight the different effects, in terms of mechanical response, caused by fibers of different size at different cracking stages of the tested materials.

Steel fiber reinforced self compacting concrete has high potential application in structural elements. The distribution and orientation of fibers in fiber reinforced self compacting concrete play a key role in defining the mechanical and durability behavior. Several factors such as casting method and rheological properties of concrete may influence the fiber distribution and orientation within structural elements. In this paper, due to the importance of vertical elements and high uncertainties regarding fiber distribution and orientation in these elements, steel fiber dispersion and alignment were investigated. In this study, five structural walls (7.0 × 2.5 × 0.2 m) with three distinctive casting procedures (single point, double points, and continuous casting) and two rheological properties [self compacting concrete (SCC) and vibrated compacted concrete] were constructed. Thereafter, by using the inductive test, fiber orientation and distribution were assessed. The results indicated that using two casting points resulted in a more uniform fiber distribution. A comparison between the two SCC mix designs revealed that large coarse aggregates significantly increased segregation and scattering in fiber distribution and orientation. Additionally, fiber orientation analysis demonstrated that continuous casting and vibration led to greater fiber alignment in the horizontal direction. Finally, the results showed that the rheological behavior of concrete mix plays a major role in the fiber distribution compared to the casting procedure. Therefore, to achieve higher uniformity, altering mix designs is recommended.

To reduce the overexploitation of granular resources, minimize the environmental impact of fine mortars, and limit the heritage impact during the rehabilitation of old tuffeau stone buildings in the Loire Valley, France, a new coating mortar has been developed. Composed of aerial lime and tuffeau powder from sawn stone blocks, this mortar promotes the reuse of mineral waste. Due to its use as a finish coat on external insulation vertically, it requires specific characteristics in its fresh state to facilitate its application and accurately replicate the original stone's aesthetic appearance in the restored buildings. Different additives were used to optimize the material's performance: superplasticizer (SP), shrinkage-reducing agent (SRA), air-entraining agent (AEA), and rheology modifier (RM). This paper examines the fresh state behavior of the developed material by employing a methodology that combines flow table and fall cone tests. It provides an objective approach capable of assessing consistency and determining application requirements that align with the empirical properties recommended by professionals in the field. Additionally, the entrained air content and bulk density were determined. The flow table failed to identify the impact of adding AEA on application performance. However, the fall cone test revealed its influence, highlighting AEA’s role in facilitating mortar application. The SP predominantly reduced the water requirement needed to achieve specific flowability. Integrating RM with AEA enhanced the mortar’s ability to retain entrained air.

Incorporating e-waste into asphalt pavements can enhance their ability to absorb microwaves, allowing the asphalt to quickly reach its softening point under microwave exposure, flow, and fill cracks, achieving self-healing of the pavement. Depending on different heating principles, the added e-waste can be divided into two categories: microwave absorbing materials and metal shielding material. However, regardless of which material is added alone, during the microwave heating process, microwave energy will decrease along the propagation direction, leading to temperature differences in the pavement and causing uneven healing among different layers. To address this issue, this paper proposes a self-healing asphalt pavement (SHAP), where microwave absorbing materials are gradiently incorporated into the upper and middle layers of the pavement with more microwave energy, while metal reflective materials are added to the lower layer where electromagnetic energy has significantly decayed, thereby increasing the microwave absorption capacity of the pavement layer by layer. This achieves a similar warming trend across all layers after microwave heating. Based on microwave heating experiments, the effects of different added e-waste materials on the microwave heating of the pavement were studied, determining the optimal type of e-waste for each layer of the SHAP. An overall healing index (HI_average) was proposed, to maximize the HI_average, a predictive model was established using response surface methodology to determine the optimal dosage of e-waste for each layer of SHAP. Finally, a life cycle assessment demonstrated that SHAP exhibits significant economic and environmental advantages compared to conventional pavements.

Capturing the fatigue-induced evolution of viscoelastic properties of the material is crucial for predicting the fatigue life of asphalt concrete pavements. Current prediction models are often regression-based and lack accuracy, necessitating the adoption of mechanistic models like the Viscoelastic-Continuum Damage (VECD) models. The VECD models often rely on Schapery’s work potential theory and elastic-viscoelastic correspondence principles, using pseudo-strain to separate viscoelasticity from damage mechanics. However, this decoupling imposes constraints on how viscoelastic properties can evolve. This study presents a new VECD model that fully couples the viscoelasticity of the material with its damage characteristics. It was developed within a Helmholtz-potential-based thermodynamic framework, ensuring consistency with the laws of thermodynamics. The model could describe the evolution of both the apparent storage modulus and loss modulus during fatigue tests over a wide range of strain levels. It captures the three-stage fatigue behavior of asphalt concrete, allows for unconstrained variations in the apparent phase angle, and provides a clear point of failure. Moreover, it can capture the variation of fatigue life with the applied strain level in a manner similar to the Asphalt Institute fatigue life model.

Alkali-activated slag (AAS) is a low-carbon construction material and exhibits high mechanical strength and good fire resistance. However, compared to ordinary Portland cement, AAS has a greater problem in terms of resistance to carbonation. In this study, three reactive MgO and Mg(OH)₂ were used to enhance the carbonation resistance of AAS mortars. It was found that both reactive MgO and Mg(OH)₂ were able to improve the carbonation resistance of the AAS mortar, and the reactive MgO was more effective than Mg(OH)₂. Increasing the reactivity and dosage of MgO can significantly enhance the carbonation resistance of AAS mortar, resulting in a 70.5% reduction in carbonation depth. The compressive strength, phase composition, and microstructure before and after carbonation were tested, which showed that the highly reactive MgO had a greater accelerating effect on the hydration of AAS. It can not only significantly improve the compressive strength of AAS mortar but also limit the diffusion of CO₂ into the mortar. Meanwhile, the introduction of higher reactive MgO produced more hydrotalcite with a laminar structure, which could absorb a large amount of CO₃²⁻. In addition, the incompletely hydrated MgO could react directly with CO₂ during the carbonation process to achieve the purpose of carbon sequestration.

A liquid accelerator is a key component in shotcrete; however, it often faces challenges such as high alkali content and insufficient long-term concrete strength. This study utilizes polyaluminum sulfate as the primary raw material to develop an environmentally friendly, alkali-free, and fluorine-free accelerator (FAF). Through orthogonal experiments and cement compatibility tests, the effects of FAF on setting time, 1 day compressive strength, and 28 days compressive strength ratio of cement paste were analyzed, leading to the determination of the optimal FAF mixing ratio. The coagulation-promoting mechanism of FAF was further examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM) results. Additionally, concrete slab tests were conducted to assess the impact of different FAF dosages on concrete rebound rates and mechanical properties, with the optimal dosage range found to be 4–8%. Field trials indicated that, at a 6% FAF dosage, shotcrete rebound rates on tunnel arch walls and roofs were 10.3% and 13.5%, respectively. The composition of the FAF does not contain alkali metal salts, which reduces the risk of alkali-aggregate reactions in concrete and minimizes the potential health risks to construction personnel, aligning with the global trend towards sustainable construction practices.

While it is widely accepted that the steel-concrete interface (SCI) plays an important role in governing the long-term durability of reinforced concrete structures, the understanding about the primary features of the SCI that influence corrosion degradation mechanisms has remained elusive. This lack of knowledge can be attributed to, firstly, the complex heterogeneous nature of the SCI, and secondly, the absence of established experimental techniques suitable for studying the relevant SCI features. Here, we use focused ion beam—scanning electron microscopy (FIB-SEM) nanotomography to obtain high-resolution 3D tomograms of the SCI. Five tomograms, spanning volumes ranging from 8000 to ({200,000},{upmu hbox {m}^{3}}), of both non-corroded and corroded SCIs were acquired. The achieved voxel size falls within the range of 30–50 nm, which captures capillary pores highly relevant for moisture and ion transport. Potential pitfalls when applying the FIB-SEM technique to the SCI are highlighted, including aspects related to the electron detectors. We present an image processing pipeline that reduces artifacts and generates tomograms segmented into solid matrix and pore space. Furthermore, to characterize the SCI pore structure, diffusion tortuosity and porosity profiles. The analysis showed that there is a pronounced anisotropy in the pore structure. This work demonstrates that the FIB-SEM technique can be applied to acquire high resolution tomograms of the SCI pore structure, which can be digitally analyzed to inform transport models of the SCI.

This study investigates the impact of varying steel fiber (SF) content (0%, 0.8%, 1.0%, and 1.2% by volume) on the mechanical and durability properties of 3D-printed Ca(OH)₂-activated geopolymer concrete (GPC). The addition of 1.2% SF improved flexural strength by 69% at 7 days and 16% at 28 days, while tensile strength more than doubled to 3.75 MPa at 28 days. Although compressive strength remained unaffected at 43 MPa, SF enhanced interlayer bond strength by 20%, which is crucial for layer cohesion in 3D-printed structures. Additionally, the elastic modulus increased by 7%, contributing to improved stiffness. Durability assessments, including autogenous shrinkage and self-induced stress, indicated a slight reduction in shrinkage of SF-reinforced samples, with no significant effect on self-induced stress. Microstructural analysis using scanning electron microscopy (SEM) and X-ray micro-computed tomography (µCT) demonstrated the crack-bridging behavior of steel fibers, enhancing ductility and fracture resistance. There was a slight increase in porosity (5.34%) of SF-reinforced samples without negatively affecting their mechanical properties. Notably, SF improved early-age toughness and controlled crack propagation across printed layers, addressing a critical challenge in 3D-printed concrete. The novelty of this work lies in successfully reinforcing 3D-printed Ca(OH)₂-activated GPC with recycled steel fibers, enhancing mechanical properties, interlayer bonding, and durability without compromising printability. This study offers a sustainable reinforcement strategy for 3D printing in construction.