A multiphase micromechanical model for unsaturated concrete repaired by electrochemical deposition method with the bonding effects

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A multi-scale micromechanical model is proposed to predict the damage degree of hybrid fiber-reinforced concrete under or after high temperatures. The thermal degradation of hybrid fiber-reinforced concrete is generally composed of the damage of the cement paste caused by thermal decomposition and thermal incompatibility, the deterioration of aggregates and fibers, and the interfacial damage between aggregates and the matrix. In this multi-scale model, four levels of hybrid fiber-reinforced concrete structures are considered when the thermal damage degree is derived; namely, the equivalent calcium silicate hydrate (C–S–H) product level, the cement paste level, the concrete level, and the hybrid fiber-reinforced concrete level. At the cement paste level, thermal decompositions of C–S–H product and calcium hydroxide are taken into account. In addition, a dimensionless parameter of the crack density is introduced to represent the thermal cracking of the matrix. At the concrete level, the interfacial damage of aggregates is simulated by a spring–interface model, in which the interfacial parameters are assumed to be functions of temperature. Moreover, at the cement paste level and the hybrid fiber-reinforced concrete level, a sub-stepping homogenization method is proposed to determine the effective properties. Comparisons between previously published experimental data and predictions and discussions illustrate the feasibility of the proposed multi-scale model in predicting thermal damage of concrete and hybrid fiber-reinforced concrete.

Section: Model Developmentmentioning

confidence: 93%

A novel multi-scale model for predicting the thermal damage of hybrid fiber-reinforced concrete

Zhang

Zhu

et al. 2019

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“…The multilevel homogenization scheme is proved to be effective to obtain the effective properties of the multiphase composites, such as the repaired saturated concrete (Chen et al., 2015a, 2015b, 2016, 2017), the repaired unsaturated concrete (Chen et al., 2017, 2018; Yan et al., 2013) and the particle reinforced composite (Ju and Sun, 2001; Sun and Ju, 2001, 2004). The main idea of the multilevel homogenization approach can be described as follows.…”

Section: Deterministic Micromechanical Frameworkmentioning

confidence: 99%

Investigation of the unbiased probabilistic behavior of the fiber-reinforced concrete's elastic moduli using stochastic micromechanical approach

Zhu

et al. 2020

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The probabilistic behavior of the fiber-reinforced concrete is usually represented by the common probability density functions, which will lead to the biased results. This study aims to develop a stochastic multiphase micromechanical framework with Legendre orthogonal polynomial to investigate the unbiased probabilistic behavior of the fiber-reinforced concrete's moduli. The different phase volume fractions are analytically calculated based on the aggregate grading and the material's effective properties are quantitatively reached by employing the multilevel micromechanical homogenization schemes. The Monte Carlo simulations are adopted to attain the different order moments of fiber-reinforced concrete's effective properties, with which the unbiased probability density functions are reached by using the Legendre orthogonal polynomial approximations and the linear transformations. Numerical examples indicate that the proposed framework is accurate and computationally efficient to characterize the fiber-reinforced concrete's probabilistic behavior.

“…According to the similarity of the damage and healing process for the MD-based model and the CDM-based model, the net damage variable dnet has the same expression as that in previous work (Chen et al., 2018a, 2018b; Hong et al., 2015a, 2015b, 2016a, 2016b; Ju et al., 2012a, 2012b; Wu and Ju, 2017; Yan et al., 2019; Yang et al., 2017; Zhang et al., 2019; Zhou et al., 2017). At high temperatures, the net damage variable dnet decreases and the material can be healed.…”

Section: Simulation Detailsmentioning

confidence: 99%

The damage and healing of quartz under radiation at high temperatures

Zhou

2019

The effect of radiation on silica has attracted significant attention due to its potential application where radiation exists. However, the nature of the atomistic defects of quartz formed during the radiation-induced damage at high temperatures has not been fully elucidated. Molecular dynamics is adopted to investigate the damage-healing behavior of the quartz at high temperatures in this research. The ensuing diffusion and recovery of point defects in the irradiated specimen at high temperatures are simulated. The high temperature reduces the number of point defects. At 1400 K, all point defects are removed, while only some point defects are erased at 700 K. It is illustrated that the over-coordinated atoms are the main source of point defects at 300 K and 700 K. The temperature influences the configuration of point defects. The healing variable of the molecular dynamics model is subsequently developed to describe the healing process. The healing mechanisms of the irradiated specimen at high temperatures are summarized by analyzing the trajectories of atoms in detail. These results are helpful to understand the nature of radiation damage in quartz at high temperatures.