Materials and Structures最新文献

Previous studies have shown the feasibility of using recycled aggregates in new concrete production. However, the recycling of fibre-reinforced concrete (FRC) introduces a novel challenge: the emergence of a new aggregate type that can be identified as recycled aggregate with embedded fibres. Therefore, in this study, in order to investigate the differences, the mechanical properties and microstructures of polypropylene fibre-reinforced concrete (PPFRC) made of natural coarse aggregate, coarse recycled aggregate and coarse recycled aggregate with embedded fibres were compared. Polypropylene fibre contents of 3 and 9 kg/m³ (0.33% and 1.0% by volume, respectively) were chosen for all concretes. The mechanical properties, including stress–strain behaviour in compression and flexural behavior, were tested. Scanning electron microscopy (SEM) was used to examine the microstructure and elucidate the effects of different aggregates on PPFRC properties. The results indicated that recycled aggregate with embedded fibres did not enhance compressive strength and elastic modulus compared to recycled aggregate without fibres. However, when the fibre content is low, its contribution to flexural behavior is significant, even surpassing that of PPFRC made with natural aggregate.

This study presents the development of a novel Hybrid Laminate Material (HLM), particularly a dual-layered system combining an Ultra High Performance Fiber Reinforced Concrete (UHPFRC) and a Fire Resistant Geopolymer (FRG). The novel material is engineered to provide blast and impact as well as fire resistance, seeking to address the critical challenge of explosive spalling of concrete under high and rapidly rising temperatures while preserving structural integrity to withstand blast and impact loads. The FRG layer composition is optimized for environmental friendliness and cost, while assuring the formation of refractory phases at high temperatures to ensure adequate resistance to extreme temperatures. In parallel, a blast and impact-resistant UHPFRC layer is further optimized, aiming to provide exceptional compressive and flexural strength while minimizing fiber content and cost. The results highlight the development of a promising HLM that offers an environmentally friendly, cost-effective solution for enhancing the safety and resilience of critical infrastructure, incorporating robust, multifunctional building materials that can resist blast, impact, and endure extreme thermal conditions. The two layers demonstrate excellent results in their respective functions. The developed FRG successfully maintained its compressive strength while withstanding temperatures up to 1050 °C. Furthermore, an environmentally friendlier UHPFRC was designed, including 2% steel and 1% Polyvinyl Alcohol (PVA) fibers, without sacrificing the capacity to withstand blast and impact.

Geopolymers have generated interest due to their potential to be used as an alternative binder to Portland cement. This study investigated the effects of sodium and magnesium sulfate attack on metakaolin-based geopolymer mortars (MK) considering different concentrations of silica in the activator (Ms), Na₂O/MK ratio, and the inclusion of an air-entraining additive. Geopolymer mortars prepared with metakaolin and a combination of Na₂SiO₃ and NaOH were cured for 84 days. The visual appearance, linear dimensional change, mass variation, and microstructure were monitored during two weeks of immersion in a Na₂SO₄ and MgSO₄ solution at 40 ºC to understand the behavior of this material in early ages. The results indicated that the highest compressive strength was achieved with Ms = 1.5 and Na₂O/MK content of 22%. The addition of the air-entrainer to the geopolymeric mixtures minimized the expansion of the samples. This effect was attributed to the accommodation of the expansive phases in the air bubbles. The sulfate resistance of the geopolymeric material is significantly dependent on the dosage and different performances were found in the first weeks of exposure to sulfates.

This study examines the impact of asphalt emulsions produced from ionic (cationic and anionic) and non-ionic emulsifiers on the properties of cement asphalt mortar (CAM) concerning to high-speed rail slab track applications. Fresh and hardened mortar properties, such as flow time, material separation, and compressive strength are critical CAM properties considering specific application requirements in Shinkansen slab track systems. CAM were produced with asphalt emulsions of different polarity. Rheological, surface, and thermal properties were studied to understand the behavior of the mortar at different scales. Results reveal that CAM with anionic emulsions offers better stability and workability in cement environments compared to non-ionic and cationic emulsions. The evaluation of the thixotropic behavior of cement asphalt pastes revealed that cationic emulsion-based pastes exhibited higher flocculation over time. Material separation tests of hardened mortar properties show that CAM with cationic emulsion leads to the highest homogeneity, followed by non-ionic emulsions, while anionic emulsions result in poor homogeneity and the highest material separation. This behavior is attributed to the adaptability of asphalt emulsion to fine aggregates. Compressive strength study indicates that using cationic emulsions in CAM production enhances early strength (1 day), whereas CAM with anionic emulsions show delayed setting with relatively low early strength but higher later strength (28 days) due to the selective adsorption of asphalt droplets over cement phases. Considering flow time, material separation, and compressive strength, CAM with non-ionic emulsions exhibits balanced performance and is suitable for producing CAM with the desired characteristics.

This study investigated the influence of the coupling of load and corrosion environment on the fatigue properties of studs. Static tests were conducted on two push-out specimens, and fatigue tests were performed on six push-out specimens after three cycles of corrosion and fatigue alternation. The findings were compared with fatigue test results from push-out specimens subjected to pure corrosion. The analysis focused on the effects of the load and corrosion environment coupling on failure modes, fatigue life, fatigue crack length, and relative slip at the interface of the studs. The results indicated that the failure modes of all push-out specimens in both static and fatigue tests were stud shear failure. Shear failure occurred at the root of studs. Furthermore, the fatigue life of the studs decreased exponentially as corrosion ratios increased. An increase in the number of pre-fatigue cycles intensified the coupling effect of load and corrosion environment on fatigue life. The length of the fatigue fracture surface in the studs also exhibited an exponential decrease with increasing corrosion ratios. Additionally, higher corrosion ratios and a greater number of pre-fatigue cycles resulted in an accelerated the relative slip growth rate at the interface between concrete flange slabs and steel girders. The relative slip curve at the interface displayed a distinct two-stage development pattern: a stable growth stage and a rapid growth stage. The coupling effect of load and corrosion environment significantly enhanced the relative slip growth rate at the interface. This effect was amplified with increased pre-fatigue cycles and higher corrosion ratios, leading to a faster relative slip growth rate at the interface.

The growing need to enhance our road infrastructure has driven the development of several innovative techniques in recent years. Among these advancements, encapsulated rejuvenator solutions for extrinsic self-healing asphalt have emerged as a significant topic of interest. This paper evaluates the effect of optimised capsules containing vegetal oil as a biorejuvenator on the physical, mechanical, and self-healing properties of dense asphalt mixtures. In this study, previously optimised polynuclear alginate-based capsules were synthesised using vibrating jet technology with 5% wt. calcium chloride and a biopolymer-to oil mass ratio 1:7. Optimised capsules were incorporated into the asphalt mixture at concentrations of 0.125% wt., 0.25% wt., and 0.5% wt. Their spatial distribution within the asphalt mixtures was evaluated using an alternative method to CT scans, which utilised machine learning-based image analysis of the core asphalt samples. The main findings of this research are as follows: (1) a uniform distribution of capsules was achieved throughout the asphalt mixture, although clustering was observed at higher concentrations. (2) The capsules successfully survived the asphalt manufacturing process, and mechanical tests highlighted the adhesive properties of the alginate encapsulation material. (3) Asphalt samples with 0.125% wt. capsules exhibited mechanical performance comparable to samples without capsules; however, this content did not significantly enhance their self-healing properties. In contrast, self-healing capabilities were significantly enhanced with a capsule content greater than or equal to 0.25% wt.; however, this enhancement slightly affected some physical–mechanical properties of the dense asphalt mixture.

The diffusion coefficient (D_ic) is an essential parameter that helps to understand various durability issues in concrete, like corrosion, alkali-silica reaction (ASR), and freeze-thaw damage. However, most research in this area has focused on homogeneous materials like paste and mortar, while concrete has proven to be challenging because of its inhomogeneous nature. This study used dental X-ray equipment adapted for transmission X-ray measurements to measure ion diffusion. This device is named CHIP (Checking Ion Penetration). This work applies the CHIP on 104 paste and 104 concrete samples with hydration times between 45 and 1100 days. This work improved the accuracy by combining measurements from multiple angles and correcting for X-ray beam hardening. This approach improved the accuracy of concrete D_ic measurements by 20% (as indicated by R square) while reducing variability (expressed as the coefficient of variation) by 63%.

In the research described in this paper, we prepared low-cost multiphase composites based on calcium sulfoaluminate (also known as ye’elimite) and fluorapatite. By utilizing the CaO originally present in fluorapatite, the sintering densification of these composites was enhanced. The influence of varying the SiO₂ content (0–5.4 wt.%) on the reactive sintering of fluorapatite, bauxite, and gypsum was investigated. Incorporating quartz led to the formation of various compositions, including calcium hexaluminate, fluorapatite, ye’elimite, and gehlenite. Quantitative phase analysis, conducted using the Rietveld method via Profex software at various sintering temperatures, demonstrated a relationship between quartz content and the preferential formation of gehlenite over ye’elimite within the 1300–1350 °C range. Additionally, the microstructure of the composites was significantly modified by quartz addition, leading to the development of hexagonal and circular grains after heat treatment at 1400 °C.

For the additive manufacturing in civil engineering, the cementitious ink must have contradictory properties to be printable, indeed it must be initially fluid enough to be pumpable and extrudable, and also should stiffen quickly after deposition to be buildable. These can influence the mechanical properties and the behavior of the printed structure. This work is focused on the role of the printing conditions, mainly time gap between successive layers and environmental conditions, on the quality of the interface between printed layers. The mechanical properties of the interface were studied by means of classical and instrumented indentation tests at micro and macroscopic scales jointly to bidirectional macro compression tests. In addition to the macrohardness tests, microindentation allows to study the role of the interface at a local scale by applying the interfacial weakness criterion based on a hardness profile established on a cross-section in the neighborhood to the plane of the interface. The influence of the printing conditions on the mechanical behavior of the interface is clearly highlighted. As an example, this criterion shows a degradation of the interface property with an increase in the time gap between layers in addition to the influence of the thermo-hygrometric conditions. For a better understanding of the mechanical behavior at the interface, additional instrumented indentation tests in the plane of the interface using macro-loads are carried out until the rupture. The critical load of fracture confirms the role of the printing conditions, whereas the compression tests are not able to show significant differences between the elaboration conditions. The indentation test, which is not widespread in the field of civil engineering, proves here that it can be very useful for a finest mechanical characterization of the material, especially for the characterization of the interface at a local scale.

To ensure the efficient production of calcined clays at an industrial scale, rapid testing method is required to prevent under or over- calcination and guarantee proper quality control. This study investigates the phase transformation processes of six kaolinitic clays calcined between 400 and 1000 °C, using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. The results confirm that the formation of spinel phase indicates over-calcination as approximately 50% reduction was observed in pozzolanic reactivity at 1000 °C. The influence of various common impurities such as quartz, iron and 2:1 clay mineral on the onset of over- calcination has been studied. The impurities and crystallinity of kaolinite were found to influence only the temperature at which spinel forms and not the quantity. Highly disordered iron rich clays showed approximately 50 °C lower temperature than ordered quartz rich kaolinite clay. DSC proved effective in detecting the presence of spinel, which is not easily identified in other techniques. The combination of TGA and DSC can therefore be used not only to assess and quantify if a clay is properly calcined or not, but also to identify the optimal calcination temperature. Furthermore, practical guidelines for implementing DSC as a quality control tool for calcination are provided that would offer valuable insights for industrial applications.