Behavior of Concrete Permeability Considering ITZ

A stochastic micromechanical framework for predicting the concrete probabilistic behavior is proposed considering the interfacial transition zone effects in this paper. The volume fraction of the interfacial transition zone is analytically calculated based on the aggregate grading. Multilevel homogenization schemes based on the direct interaction micromechanical solutions are presented to predict the concrete effective properties considering the aggregate and interfacial transition zone effects. By modeling the volume fractions and properties of the constituents as stochastic, we extend the deterministic framework to stochastic to incorporate the inherent randomness of effective properties among different concrete specimens. With the moments of the effective properties, the probability density function is approximated using the exponential polynomial for concrete material. Numerical examples including limited experimental validations, comparisons with existing micromechanical models, commonly used probability density functions, and the direct Monte Carlo simulations indicate that the proposed models provide an accurate and computationally efficient framework in characterizing the material’s effective properties. Finally, the effects of the randomness of interfacial transition zone and aggregate on the materials’ macroscopic probabilistic behaviors are investigated based on our proposed stochastic micromechanical framework.

The interfaces between the deposition products and concrete are not always well bonded when the electrochemical deposition method (EDM) is adopted to repair the deteriorated concrete. To theoretically illustrate the deposition healing process by micromechanics for saturated concrete considering the imperfect interfaces, an improved micromechanical framework with interfacial transition zone (ITZ) is proposed based on our recent studies. In this extension, the imperfect bonding is characterized by the ITZ, whose effects are calculated by modifying the generalized self-consistent model. Meanwhile, new multilevel homogenization schemes are employed to predict the effective properties of repaired concrete considering the ITZ effects. Moreover, modification procedures are presented to reach the properties of repaired concrete with ITZs in the dry state. To demonstrate the feasibility of the proposed micromechanical model, predictions obtained via the proposed micromechanical model are compared with those of the existing models and the experimental data, including results from extreme states during the EDM healing process. Finally, the influences of ITZ and deposition product on the healing effectiveness of EDM are discussed based on the proposed micromechanical model.

Unraveling the Stray Current-Induced Interfacial Transition Zone (ITZ) Effect on Sulfate Corrosion in Concrete

Effect of interfacial transition zone on the transport of sulfate ions in concrete

3D mesoscale investigation on the compressive fracture of concrete with different aggregate shapes and interface transition zones

Concrete might be subjected to impact or blast loading. To analyze the concrete behaviors under such loading cases, it is of interest to study the dynamic damage and failure behavior of concrete under high strain rate. In the present paper, a mesoscale model is developed to numerically analyze the dynamic damage process of concrete samples under high strain rate tension. In the mesoscale model, the concrete is regarded as a three-phase composite consisting of coarse aggregate, mortar matrix, and interfacial transition zone (ITZ) between the aggregate and the mortar matrix. Different coarse aggregate shapes, such as circular, oval, and polygon, are calculated and compared. It is found that the shapes of the coarse aggregates do affect the tensile strength and failure pattern.

Concrete is a multiphase composite material, in which the mortar, aggregate and interfacial transition zone (ITZ) have important influence on the chloride ions transport. In this research, the thickness ITZ was measured and the concentration distribution of chloride ions in concrete was obtained through electron microprobe analysis. The experiment results that the thickness of ITZ follows a normal distribution and the size of aggregate shows no clear influence on the thickness of ITZ.

Predicting peak tensile stress in mesoscale concrete considering size effects: A data-physical hybrid-driven approach

Nano/microcharacterization and image analysis on bonding behaviour of ITZs in recycled concrete enhanced with waste glass powder

Two-dimensional meso-scale finite element models with real aggregates are developed using images obtained by digital image processing to simulate crack propagation processes in concrete under uniaxial compression loading. The finite element model is regarded as a three-phase composite material composed of aggregate, mortar matrix and interface transition zone (ITZ). Cohesive elements with traction–separation laws are used to simulate complex nonlinear fracture. During the experiment, digital image correlation (DIC) was used to obtain the deformation and cracks of the specimens at different loading stages. The concept of strain ratio is proposed to describe the effectiveness of simulation. Results show that the numerical strain ratio curve and stress–strain curves are both in good agreement with experimental data. The consistency between the cracks obtained by simulation and those obtained by DIC shows the good performance of cohesive elements as well as the effectiveness of simulation. In summary, the model is able to provide accurate predictions of the whole fracture process in concrete under uniaxial compression loading.

Surgically Inspired Technique of ITZ Integration in Lattice Model for Numerical Simulation of Cement Composites

Considering the heterogeneity, a mesoscopic simulation method was developed to analyse the heat conduction behaviour of heterogeneous concretes. In the numerical homogenisation technique, the concrete was regarded as a heterogeneous material consisting of three components (aggregate, mortar matrix and interfacial transition zones (ITZs)). Both two- and three-dimensional random aggregate structures of concrete were established. The temperature-dependent thermal properties of the mortar and aggregate were obtained based on experimental data from the literature, and those of the ITZ were determined by comparing the simulation results with measured values. The heat conduction equations were solved using the finite-element method: the three components were meshed separately and continuity of the heat fluxes at interfaces was applied. Good agreement was found between the simulation results and available test observations. The simulation results indicate that both the effective thermal conductivity (ETC) and a more accurate temperature field of concrete can be obtained using this mesoscale simulation method considering the temperature dependency of the materials' thermal properties. Aggregate shape was found to have a negligible influence on the ETC of concrete, but the type of aggregate cannot be ignored due to their different thermal conductivities. The ETC of concrete increased with increasing aggregate content and decreased with increasing temperature.

Three-dimensional reconstruction and sulfate ions transportation of interfacial transition zone in concrete under dry-wet cycles

The permeability of chloride ion in concrete can be studied using the accelerated aging method in a short period, but the influence of loading characteristic on chloride ion permeability and diffusion coefficients is not considered generally. Three RC beam (120 mm×240 mm×2400 mm) specimens with different flexural loading state are exposed in an artificial corrosion container filled with salt-fog of 5.0 % sodium chloride for 40 days, the chloride ion concentration in different depths of compressive and tensile region are measured, diffusion coefficients of different region concrete are fitted on the basis of Fick’s second law, the effect of flexural loading on chloride ion concentration and diffusion coefficients of concrete are analyzed. The results show that the effect of the flexural load influences permeability of chloride ion and diffusion coefficients of concrete, content of chloride and diffusion coefficients of concrete are controlled by loading level, and the bending load is one of the important factors that can not be ignored in the study of concrete durability.

Study on the penetration and diffusion of chloride ions in interface transition zone of recycled concrete prepared by modified recycled coarse aggregates