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Mesoscale model for cracking of concrete cover induced by reinforcement corrosion
Junyu Chen,Weiping Zhang,Xianglin Gu 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.1
Cracking of concrete cover induced by reinforcement corrosion is a critical issue for life-cycle design and maintenance of reinforced concrete structures. However, the critical degree of corrosion, based on when the concrete surface cracks, is usually hard to predict accurately due to the heterogeneity inherent in concrete. To investigate the influence of concrete heterogeneity, a modified rigid-body-spring model, which could generate concrete sections with randomly distributed coarse aggregates, has been developed to study the corrosion-induced cracking process of the concrete cover and the corresponding critical degree of corrosion. In this model, concrete is assumed to be a three-phase composite composed of coarse aggregate, mortar and an interfacial transition zone (ITZ), and the uniform corrosion of a steel bar is simulated by applying uniform radial displacement. Once the relationship between radial displacement and degree of corrosion is derived, the critical degree of corrosion can be obtained. The mesoscale model demonstrated its validity as it predicted the critical degree of corrosion and cracking patterns in good agreement with analytical solutions and experimental results. The model demonstrates how the random distribution of coarse aggregate results in a variation of critical degrees of corrosion, which follows a normal distribution. A parametric study was conducted, which indicates that both the mean and variation of critical degree of corrosion increased with the increase of concrete cover thickness, coarse aggregates volume fraction and decrease of coarse aggregate size. In addition, as tensile strength of concrete increased, the average critical degree of corrosion increased while its variation almost remained unchanged.
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Junyu Zhang,Haoran Sun,Xiaotian Shui,Wenxuan Chen 한국콘크리트학회 2024 International Journal of Concrete Structures and M Vol.18 No.2
Pervious concrete (PC) as a green infrastructure material has been increasingly used due to its positive environmental impacts, such as controlling storm water runoff, removing water pollutants and reducing heat island effect. The aggregate gradation is a critical factor influencing the physical properties of PC. Therefore, this paper represents an attempt to determine the effects of aggregate gradation on the various physical properties of PC, and then to explore relationships between them. To this end, three aggregate gradations 4.75–9.5 mm, 9.5–19 mm and 19–31.5 mm were recombined with various proportions (20–80%) to obtain five different gradations named as A, B, C, D and E. PC mixtures were prepared with these five aggregate gradations. Then, physical and mechanical properties of PC including porosity, permeability, compressive strength and water stability were investigated, according to the available specification. The results suggested that it was feasible to use waste concrete for permeable pavement, because all the specimens provided required specification requirements. Different linear relationships were also found between the maximum aggregate size and porosity, permeability coefficient, compressive strength and its loss rate. That is, porosity and permeability increased with the proportion of larger size aggregate increased, however, compressive strength reduced. Thus the compressive strength had an inverse correlation with the porosity and water permeability. Among five different aggregate gradations, group C (20% of 4.75–9.5 mm aggregate, 50% of 9.5–19 mm aggregate and 30% of 19–31.5 mm aggregate) can be seen as the optimum gradation and is suitable for base layer materials of permeable pavements.
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Yuanyuan Qin,Yifei Wang,Jin Liu,Fengfeng Chen,Aiying Yao,Zhanchun Chen,Fu Junyu 한국고분자학회 2022 Macromolecular Research Vol.30 No.12
The mechanical properties of functionalized graphene/polyethylene (f- GRA/PE) composites and graphene/polyethylene (GRA/PE) composites were studied based on the crystallized models with the molecular dynamics simulation in this paper. The effects of GRA and f-GRA with different mass fractions on the mechanical properties of polyethylene were considered. The results showed that the adsorption capacity of polyethylene molecular chains of f-GRA is stronger, the compatibility of f-GRA/PE system is higher with decreasing the interface distance, and the dynamic property of molecular chain is weaker with reducing the radius of gyration of f-GRA/ PE. Furthermore, the reduction of mechanical energy consumption results in the increase of wear resistance of the system, which is more obvious when the mass fraction of f-GRA increases. Finally, the influence of different tensile rates on the composite system was studied. It was found that during the tensile process, the ability of the composite material to resist deformation in the stretching direction is enhanced, and the functionalized graphene inhibits the movement of the molecular chain due to the adsorption force, which improves the yield stress of the f-GRA/PE composite material, thereby increasing the tensile strength. Tensile rate has a certain effect on mechanical properties, and elastic modulus and yield stress increase with the increase of strain rate.
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Xuezhi Li,Yuanyuan Qin,Haojie Li,Guangjun Liu,Junyu Fu,Feng Li,Zhanchun Chen 한국고분자학회 2023 Macromolecular Research Vol.31 No.9
The processability and practical applications of poly (butylene adipate-co-terephthalate) (PBAT) /poly (lactic acid) (PLA) blends are limited due to their lower miscibility. To investigate the miscibility of various PBAT/PLA composite ratios and the mechanism of miscibility between them, PBAT/PLA blends with different ratios were prepared using the melt mixing method. A combination of multi-scale simulations and experiments were employed to investigate the miscibility of the composites. Molecular dynamics simulations analyzed PBAT/PLA mixtures that are incompatible and showed the molecular basis of their incompatibility through the radial distribution function (RDF). The degree of miscibility of different ratios of PBAT/PLA composites was described using the Flory–Huggins interaction parameter, indicating that the 50/50 PBAT/PLA blend has the worst miscibility. Mesoscopic dynamics described the mesoscopic morphology of PBAT and PLA blends visually. The results obtained from the simulations were consistent with scanning electron microscope (SEM) and differential scanning calorimeter (DSC) experiments, indicating the simulations' reliability. This work provides a molecular perspective on the mechanism of thermodynamic insolubility of PBAT and PLA, which can inspire future PBAT/PLA hybrid modifications.
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