Concrete structures are prone to damage from various factors, particularly chloride ion penetration, which can lead to premature deterioration. Although self-repairing materials can mitigate damage ...and erosion, methods for evaluating their efficacy are lacking. This study explores concrete damage development, chloride and water transport in damaged concrete, and post-repair transport behavior. A comprehensive mechanical-transport-healing model for concrete was established to investigate the influence of damage and self-healing rates on chloride distribution. Results show that tensile loads under 5 μm have minimal impact on concrete transport, whereas larger displacements significantly accelerate water and chloride migration. This acceleration resulted in a 66 % increase in the chloride concentration at a depth of 15 mm with a displacement of 10 mm. Higher self-healing rates effectively reduced the chloride concentration within the 10–30 mm range. Increasing the healing rate from 70 % to 90 % led to 75 % and 35 % decreases in the chloride concentration at a depth of 30 mm after 100 years, respectively. These findings provide valuable insights into the relationship between the mechanical damage and chloride transport in concrete, which can inform the development of strategies for enhancing the durability of concrete structures exposed to chloride-rich environments.
•A coupled mechanical-transport-healing numerical model is developed.•The relationship between damage on the acceleration of concrete erosion medium transport was quantified.•The effect of self-healing rate on the transport properties of damaged concrete was calculated, and the self-healing rate requirement for damaged concrete was proposed.
•Finite element model predicts HSR concrete fatigue life.•Model assesses impact of load frequency, stress ratio, and level.•Fatigue life of environmentally damaged concrete analyzed.
High-speed ...railways have become a critical component of modern transportation, and ensuring the stability and durability of high-speed railway concrete under environmental and train fatigue loads is essential for ensuring project safety. This paper employs a numerical simulation method to predict the performance and lifespan of high-speed railroad concrete under fatigue loading with environmental damage. The study analyzes the effects of stress level (0.5–0.8), stress ratio (0.1–0.9), and load frequency (5 Hz–40 Hz) on the fatigue performance and lifespan of railway concrete during bending fatigue loading. A four-point bending numerical model of concrete is developed in this paper, which considers elastic modulus decay and surface cracking, in order to quantify the degradation of concrete properties in response to environmental and load-induced cracks. The numerical model is well-validated with experimental results, and the study establishes a correlation between concrete degradation and environmental and load-induced cracks, as well as the fatigue resistance of high-speed railroad concrete. The bending fatigue frequency of concrete should not exceed 25 Hz at high stress levels of 0.7. This study also shows that environment-induced initial damage will greatly reduce the fatigue resistance of concrete, and fatigue life degradation and elastic modulus decay have a nearly linear relationship. This research provides a crucial foundation for the fatigue design of concrete materials for high-speed railroads.
Free-standing MWCNTs/V2O5 nanobelts composite architecture electrodes for lithium ion batteries (LIBs) are prepared based on hydrothermal method, electrostatic self-assembly approach and vacuum ...filtration deposition technique. Such kind of nanoarchitecture enhances the electrochemical kinetics and structural stability of V2O5 cathodes. The distribution and evolution features of plane strains in free-standing MWCNTs/V2O5 cathodes surface are in-operando monitored by using digital image correlation method and systematically discussed. The strain results show that the evolution of strain against potential obeys general Arrhenius relation under galvanostatic charge-discharge cycling. Considering the effect of lithium ion concentration, the elastic modulus of 20 wt% MWCNTs/V2O5 electrode is confirmed via nanoindentation. The evolutions of average plane stresses in the free-standing MWCNTs/V2O5 electrodes, as well as the contributions of mechanical and electrochemical components, are evaluated and discussed by mechano-electrochemical constitutive equation during electrochemical process. The analytical methods used in this article are universal for revealing the electrode mechano-electrochemical failure mechanism in LIBs.
•MWCNTs/V2O5 nanobelt nanocomposites were prepared by electrostatic self-assembly.•The evolution of plane strain in MWCNTs/V2O5 cathodes is in-operando monitored.•The relationship of voltage and strain was established by general Arrhenius formula.•The stresses in MWCNTs/V2O5 cathode varied with charging-discharging cycles.•The results are useful for revealing mechano-electrochemical mechanisms of LIBs.
In actual engineering, most concrete structures are unsaturated, and the transport of harmful media in concrete highly depends on its saturation degree. In this study, chloride transport in mortars ...with different saturation degrees (0, 0.2, 0.4, 0.6, 0.8, and 1.0) under two conditions was investigated. One condition was that the mortars did not exchange moisture with the outside and that the internal saturation degree was constant. The other was that the mortars were continuously immersed in 3% NaCl solution, meaning that the saturation degree increased gradually. The chloride content distribution in mortars was obtained for exposure times 6, 18, 30, and 44 weeks. From the values obtained, the relationship between the relative chloride diffusion coefficient and initial saturation degree was established. Meanwhile, based on the diffusion mechanism and the capillary effect, a convection–diffusion numerical model was proposed to simulate chloride transport in mortars. The simulation results agreed well with the experimental results, especially at depths of 0–15 mm. This work aims to make a further understanding of chloride transport in concrete, and is of great significance to assess the durability and predict the service life.
•The convection is the main factor affecting the unsaturated gel pores.•The higher number of bending will hinder the ion transport in the gel pore.•Ca2+ will weaken the diffusion capacity of ions in ...the NaCl solution.
The durability of cement-based materials is significantly influenced by the transport ability of multiple ions in gel nanopores of calcium silicate hydrate (C-S-H) that is directly associated with the degree of water saturation. In this study, the mechanism of ions transport in unsaturated C-S-H gel pores was revealed by the molecular dynamics simulation at the nanometre scale. The ions transport behaviour in gel pores was investigated via the establishment of different types of simulation models, which had different initial saturations, pore sizes and bending numbers of gel pores. The thickness of the electrical double layer was determined by the analysis of the distribution of ions, and the ions transport in C-S-H gel pores was affected by the electrical double layer. The percolation effect would appear in gel pores during the simulation from the dry state to saturated state, and it could promote the transport ability of ions significantly. However, it affected the extreme value of ion diffusion coefficient rather than the maximum value. Another result is that the bending numbers of gel pores would hurt the transport of ions. It is noted that the incorporation of Ca2+ will weaken the diffusion capacity of ions in the NaCl solution, while the reverse phenomenon is observed when K+ is incorporated.
Fast and real-time detection of trace Hg(Ⅱ) by fluorescent probes under acidic conditions is urgently required due to the high toxicity and accessibility to creatures and human being. However, ...fluorescent probes for Hg(Ⅱ) detection in environmental samples are rarely reported due to the protonation potential of acidic mercury sources. In this study, the SD probe was developed by 5-(p-dimethylaminobenzylidene) rhodanine (DMABR) loaded on sepiolite by hydrothermal treatment, and showed excellent Hg(Ⅱ) detection performances for mercury sources at pH 4–10 due to buffering ability of the hyperconjugated lactam rings. Sepiolite functioned as the support skeleton to decrease intermolecular transition, and thus increased the sensitivity. At pH 4, the SD probe showed high selectivity and sensitivity for Hg(Ⅱ) among various species, with low LOD and binding constant of 4.78 × 10−9 M and 1.34 × 106 M−1, respectively. Through DFT calculations, MAS 1H NMR and 2D-COS analysis, the detection mechanism was demonstrated as SN1 substitution of the spontaneous leaving H on amino groups in the transient state during tautomeric equilibrium, rather than the expected high-affinity sulphydryl. Additionally, the SD probe exhibited promising potential in quantifying water-soluble and bioavailable Hg(Ⅱ) in acidic polluted soil and water samples. Moreover, real-time detection was realized by paper-based strips.
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•The SD probe exhibited excellent performance in Hg(Ⅱ) detection pH 4-10.•Bioavailable Hg(Ⅱ) in soil and water samples was accurately detected by SD probe.•Real-time detection of Hg(Ⅱ) by SD probe was achieved by paper-based strips.•pH-induced tautomeric equilibrium posed the mechanism as SN1 substitution on N-H.
x mol% CeO2-YTaO4 (x = 0, 3, 6, 9, 12) ceramics have been synthesized by the spark plasma sintering (SPS) technique. We focus on the changes in lattice distortion, bonding length, thermal ...conductivity, thermal expansion, and phase stability of the prepared samples. XRD, Raman, and XPS are used to determine the chemical valence and solid solution mechanism of Ce in the lattice of YTaO4, while its effects on thermal/mechanical properties are elucidated from microstructures. Y3+ is substituted via Ce3+, and all samples maintain a monoclinic phase. The limit thermal conductivity (1.2 W∙m−1∙K−1, 900 °C) is realized in 9 mol% CeO2-YTaO4, and the thermal expansion coefficients are increased to 10.2 × 10−6 K−1 at 1200 °C. Furthermore, the exceptional phase stability and mechanical properties of all samples indicate that they can provide good thermal insulation at high temperatures, and have higher working temperatures than the current YSZ thermal barrier coatings.
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•CMAS corroded YSZ columnar crystal firstly from corner structure is investigated by DFT.•Deep corrodibility of CMAS/YSZ originates from its small contact angle and large adhesion ...energy.•Powerful affinity of Y and Ca elements induce t-ZrO2 transforming into c-ZrO2 easily.•Similar energy level of d orbital of Y and Ca element plays vital role in CMAS infiltration.
Through Yttria stabilized zirconia (YSZ) microfacet models, the infiltration mechanism of Ca-Mg-Al-silicate (CMAS) melt on the corner of YSZ columnar crystal at high temperature was studied by first-principles calculation. The results show that the contact angles of CMAS melt on YSZ(0 1 0 × 0 1 0), YSZ(0 1 0 × 1 0 1) and YSZ(1 0 1 × 1 0 1) are equal to 40°, 48° and 38° respectively, which exhibit hydrophilicity. Their adhesion energies Wad are also larger than that of CMAS/YSZ bulk surface. Elements diffusion points out that the large wettability of CMAS melt on the corner of YSZ columnar crystal comes from the powerful converging ability of Y and Ca elements, which have the similar energy levels of electrons at d orbital. And their large and positive charged of electrostatic potentials provide further chemical corrosion reaction of CMAS melt.
