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• The failure processes between deformed bar and concrete under monotonic pull-out and push-in loading were analyzed. • Effect of reversed loading on the shear crack development was studied. • Effect of lateral pressure on the cyclic bond deterioration of deformed bars in well-confined concrete was evaluated. The cyclic bond deterioration mechanism of deformed steel bars embedded in concrete is critical for establishing the hysteretic bond stress-slip relationship. For a deformed steel bar, well-confined in concrete, the bond failure model under monotonic loading is governed by pullout, the bond deterioration trend under cyclic loading is remains unclear, especially in the case of applied lateral pressure. In this paper, the effect of uniaxial lateral pressure on the bond performance under different loading histories was studied. The test results indicate that the variation in bond parameters under varied lateral pressure is negligible. Therefore, the monotonic and reversed bond stress-slip constitutive relationship of a deformed bar failed by pullout, without lateral pressure confinement, can be used for simulating the bond response under different uniaxial lateral pressures. Cubic concrete specimens with small openings were used to quantitatively analyze the failure process under reversed loading through digital imaging correlation (DIC). The bond stress was observed to be nearly uniformly distributed along the interface at the initial loading stage. After increasing the pull-out or push-in loading to 75 %–85 % of the peak bond strength, we observed minute shear cracks between the interfaces. Subsequently, the length and width of the cracks were then gradually developed with the controlling slip and number of cycles, leading to reduced mechanical interaction and friction between the shear cracks. [ABSTRACT FROM AUTHOR]

Concrete is modeled on the mesoscale as a heterogeneous three-phase composite consisting of mortar, aggregates and the interfacial transition zone (ITZ). By exerting a steady state flow in the concrete sample, the effective permeability is estimated using finite element method (FEM). Extensive Monte Carlo (MC) simulations for more than 1000 concrete samples are carried out. The effects of the mesostructural parameters (i.e., the shape, gradation and volume fraction of aggregates and the thickness and permeability of ITZ) on the permeability of concrete are comprehensively investigated. For a specific set of mesostructural parameters, the size of the representative volume element (RVE) for concrete permeability is suggested in terms of the expected errors by numerical and statistical analysis. It shows that computational homogenization for estimating the effective permeability of concrete in three dimensions (3D) is absolutely necessary since the two dimensional (2D) results are less representative. [ABSTRACT FROM AUTHOR]

Durability of concrete depends largely on its water permeability, which is dominated by the composition and difficultly evaluated. This paper presents a three-dimensional (3D) FE algorithm to investigate the water transport performance in concrete. This FE model possesses three-phase mesostructure consisting of coarse aggregates, mortar matrix, and the interfacial transition zone (ITZ) which is practically modeled by the zero-thickness interface element. A series of numerical tests with regard to concrete samples containing different volume fractions of coarse aggregates are conducted. The calculated permeability coefficients are in reasonable accordance with the physical experiment data. Effects of aggregates and ITZ on the concrete permeability are also quantitatively studied by the numerical test. It is proved that the proposed algorithm is capable of modeling the permeable characteristics of concrete which is affected greatly by its heterogeneous mesostructure. [ABSTRACT FROM AUTHOR]

The bond behavior of steel bars in concrete subjected to complex lateral stresses has received wide attention over the last two decades and various bond strength models and bond stress–slip relationships have been proposed. However, the knowledge of how the loading rate affects the bond behavior of steel bars remains limited. In this paper, a total of 237 pull-out specimens were tested to investigate the effect of the loading rate on the bond behavior between plain round bars and concrete under different lateral pressures. The experimental results showed that, when a lateral pressure is applied, the bond performance is greatly affected by the loading rate. For a given lateral pressure, the ultimate and residual bond strengths increase but the slip at the peak bond stress decreases with the increase of the loading rate. The larger the lateral pressure is, the more pronounced the loading rate effect is. Finally, an empirical bond stress–slip relationship considering lateral pressure, the loading rate, the strength of concrete, and the bar diameter is proposed and verified with experimental results. [ABSTRACT FROM AUTHOR]

• The evolution processes of the surface strain field and internal damage of the self-expanding grouting materials were analyzed. • Effect of density on the mechanical properties was evaluated. • A compressive stress–strain model before yielding considering the density variation was established. The compressive mechanical properties of self-expanding grouting materials with different densities are essential in evaluating the ultimate conditions of the repaired underground infrastructure. In this study, digital imaging correlation (DIC) and acoustic emission (AE) techniques were applied to monitor the compressive damage evolution process of self- expanding materials with different densities. It was found that the varied density exhibits great effect on the compressive response of self-expanding grouting materials, and that the length of the horizontal yield plateau decreases with the density. As the density increases to 0.399 g/cm3, the horizontal yield plateau diminishes and the materials present from plastic to brittle characteristics. Moreover, a statistical damage constitutive model of the ascending branch was developed and validated by experimental results. [ABSTRACT FROM AUTHOR]

• Bond properties for deformed bars in concrete under lateral pressure and cyclic loading were tested. • Effects of lateral pressure and bar diameters on the bond behavior were evaluated. • A bond stress-slip model considering the lateral pressure and cyclic loading was established. The reversed cyclic bond behaviour between steel bar and concrete is critical to simulate the hysteretic response of reinforced concrete structures suffering from seismic loading and the bond behaviour is also greatly influenced by the stress field around the bond region. The objective of this study is to investigate the influence of uniaxial lateral confinement on the bond response of deformed bars in concrete under variable-amplitude reversed cyclic loading. The effect of lateral pressure and bar diameter on the bond parameters under reversed loading were evaluated. In addition, a hysteretic bond stress-slip constitutive model considering the uniaxial lateral confinement was proposed and validated with the test results. [ABSTRACT FROM AUTHOR]

The composite modifier (CM) of asphalt concrete (AC) mixture containing crumb tire rubber, recycled plastic particles, and SBS was developed. The main objective of this study was to evaluate the effect of CM on the performance of AC mixture. Wheel tracking test, beam bending test, freeze-thaw indirect tensile test, and bending creep test of CM modified AC mixtures and the control mixture (AC mixture without CM) were conducted in laboratory. The results show the addition of CM in AC mixtures can significantly improve high temperature performance compared to the control mixture, but the unsuitable dosage of CM may have some adverse effect on low temperature performance and moisture susceptibility. Considered comprehensively, the optimum dosage of CM was determined to be 0.3%. The relationship between the low temperature performance and CM dosage was verified by the m / S and dissipation energy ratios ( W d / W s ) calculated using Burgers model parameters of the bending creep at 0 °C. Compared to the control mixture, the values of permanent deformation and creep rate of CM modified AC mixture were smaller, and the values of the parameters E 1 and η 1 of Burgers model for the bending creep at 35 °C were larger. It can be further verified that the addition of CM obviously improves permanent deformation resistance of AC mixtures at high temperature. [ABSTRACT FROM AUTHOR]

The composite modifier (CM) of asphalt concrete (AC) mixture containing crumb tire rubber, recycled plastic particles, and SBS was developed. The main objective of this study was to evaluate the effect of CM on the performance of AC mixture. Wheel tracking test, beam bending test, freeze-thaw indirect tensile test, and bending creep test of CM modified AC mixtures and the control mixture (AC mixture without CM) were conducted in laboratory. The results show the addition of CM in AC mixtures can significantly improve high temperature performance compared to the control mixture, but the unsuitable dosage of CM may have some adverse effect on low temperature performance and moisture susceptibility. Considered comprehensively, the optimum dosage of CM was determined to be 0.3%. The relationship between the low temperature performance and CM dosage was verified by the m / S and dissipation energy ratios ( W d / W s ) calculated using Burgers model parameters of the bending creep at 0 °C. Compared to the control mixture, the values of permanent deformation and creep rate of CM modified AC mixture were smaller, and the values of the parameters E 1 and η 1 of Burgers model for the bending creep at 35 °C were larger. It can be further verified that the addition of CM obviously improves permanent deformation resistance of AC mixtures at high temperature. [ABSTRACT FROM AUTHOR]

• The effect of polymer density and interfacial moisture on the bond behavior was evaluated. • Correlation between bond strength and microstructural features was analyzed. • Bond mechanism between self-expansion polymer and concrete was characterized. Polymer grouting technology is a new trenchless method to restore leakage and subsidence of underground concrete structures, and the bond between polymer and concrete is critical to estimate the deformation and ultimate conditions of the repaired structures. In this paper, scanning electron microscopy (SEM) and a series of direct shear tests were used to evaluate the interfacial bond properties between self-expansion polymer and concrete. Based on the test results, the effect of polymer density, the strength of concrete, the moisture content of grouting interface before and after grouting on interfacial microstructure, failure mode, shear stress-slip curves, and bond capacity were evaluated and discussed. The results demonstrated that the polymer could infiltrate into the pores of the concrete grouting surface, the infiltrate value and the polymer strength increased with the amount of grouting and resulted in large bond strength. Pre-moistened the grouting surface reduce the polymer migration into the irregularities of the concrete substrate and affect chemical reactions, show un-full filled pores of the interface and increased the diameter of the polymer cells around the interface, which is thought to exerts a negative influence on the bond behavior. [ABSTRACT FROM AUTHOR]

The self-restraint thermal stress caused by mismatch in thermal and mechanical behaviors of cementitious material and coarse aggregates could be a factor associated with early-age cracking in massive concrete structures, which might be even complicated when considering the mesostructure of concrete. This paper presents the application of mesoscopic model based numerical approach to trace the progression of thermo-mechanical mismatch and consequent self-restraint thermal stress development during early-age hydration in concrete. The mesostructure of concrete sample which contains aggregates, mortar and ITZ is modeled, with the material properties for each phase rationally incorporated. Thermo-mechanical behaviors of both homogeneous mortar and heterogeneous concrete samples under standard curing condition are simulated, focusing on the production mechanism of self-restraint stress. Numerical results show that the spatial-time distribution of temperature and expansion coefficient fields in concrete samples is the main origin of the self-restraint stress. The magnitude of this stress is non-negligible, which may become an influential factor to the load-bearing capacity of concrete. [ABSTRACT FROM AUTHOR]