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Concrete structures in cold regions are exposed to cyclic freezing and thawing environment, leading to degraded mechanical and fracture properties of concrete due to microstructural damage. While the X-ray micro-/nano-computed tomography technology has been implemented to directly observe concrete microstructure and characterize local damage in rec...
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Under cold environments, the freezing and thawing cycles of water in concrete reduce the lifetime and durability of concrete structures. For enhanced freezing and thawing resistance, entrained air voids are generally required, but malfunctioning of air entrainment is sometimes reported in the field. To evaluate the quality of air entrainment, this...
Cold weather concrete construction under sub-zero temperatures presents challenging problems for the professionals involved in construction industry and are the main reason for poor development of such regions. Freezing of concrete before it gains required minimum strength at early age together with considerable retardation in setting time due to f...
In this research, the effect of minimum freezing temperature, freezing inhibitor concentration (NaCl), proportioning (water cement ratio, sand cement ratio) on salt scaling using the small piece test method were examined. The following results were obtained.
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Citations
... Song et al. [20] established a numerical model of freeze-thaw sandstone and investigated the evolution of microcrack derivation and fracture in freeze-thaw rock under load. Using computed tomography microstructure images and simulation models, Dong et al. [5] demonstrated that microcracks caused by freeze-thaw action are the primary reason for the degradation of concrete's mechanical properties. Most numerical studies treat asphalt as a homogeneous material and simplify the loading process as a linear elastic problem [22]. ...
To investigate the meso-mechanical behavior of heterogeneous asphalt mixtures more effectively, a discrete element method (DEM) model was developed and used to simulate uniaxial compression tests. The Weibull distribution function was introduced into the model to characterize the heterogeneity of asphalt particle contact strength, and a nonlinear damage equation derived from linear damage theory was utilized to simulate the initial damage evolution process of the asphalt mixture. The results show that: (1) After 5, 10, and 15 freeze–thaw cycles, the peak stress of the asphalt mixture decreased by 12.2%, 18.7%, and 24.9%, respectively, while the peak strain increased by 1.92%, 6.14%, and 16.1%, consistent with experimental results. (2) Both simulation and experimental damage variable evolution diagrams exhibit an ‘S’ shape, and the Weibull function effectively expresses the heterogeneous characteristics of the asphalt mixture. (3) The shape parameter m characterizes the peak stress and brittleness of the material, while the scale parameter a characterizes its deformation capacity.
... Variations in the temperature of the immediate environment have a significant effect on concrete in these locations. Few studies have focused on thermal cycling, and the majority of previous studies on the effects of temperature centered on fire disasters (Jiang et al., 2023;Thanaraj et al., 2020;Yin et al., 2022;Zhang et al., 2020Zhang et al., , 2022Zhao et al., 2023) and freeze-thaw cycles (Dong et al., 2018;Liu et al., 2022;Luo et al., 2018). The damage mechanisms of thermal fatigue and damage caused by fire are different. ...
The vast changes in temperature are what produce thermal fatigue damage to concrete. In this study, concrete specimens in three different categories—C20, C40, and C60—are tested for thermal fatigue at temperatures ranging from 10°C to 80°C in an atmosphere with constant relative humidity. Utilizing ultrasonic nondestructive testing, the elastic modulus of concrete is determined. After thermal cycling, the mass reduction and appearance of samples are also recorded. The results demonstrate that the degrading effects of thermal fatigue clearly influence concrete. As the thermal cycle lengthens, the elastic modulus of concrete rapidly decreases, and C60 concrete experiences a greater reduction in elastic modulus than C20 concrete. With thermal cycles, the damage factor increases and the ultrasonic wave velocity steadily decreases, suggesting a propagation of the concrete’s interior microcracks. Additionally, the micromechanical thermal fatigue model is developed based on the experimental results. The ability to simulate and describe the physical behavior of concrete under thermal fatigue stress on the microscale is validated by the proposed micromechanical damage model.
... 8,9 Additionally, laboratory core sampling for property testing has been extensively used to investigate the mechanical behaviors of concrete structures under freeze-thaw cycling, however, this labor-intensive approach compromises the integrity of concrete structures and fails to provide real-time information. 10,11 Worse still, it merely produces a localized measurement, unable to be generalized to the entire structure. Advanced testing techniques, such as ultrasonic testing, acoustic emission (AE), nuclear magnetic resonance (NMR), X-ray computed tomography (CT), digital image correlation (DIC), etc., have proven effective in monitoring the cyclic freeze-thaw damage of concrete structures and offering accurate measurements of concrete internal conditions. ...
Cold regional tunnels extensively suffer from severe damage in concrete linings under cyclic freeze-thaw environment. Therefore, accurate detection and evaluation of cyclic freeze-thaw damage within lining concrete is of great significance to help grasp structural health state and guarantee timely maintenance. This study pioneered the application of electromechanical impedance (EMI) method to monitor the freeze-thaw damage in bended concrete beams. The mass loss and flexural strength degradation of concrete beams under two different bending loads were thoroughly assessed to quantify the evolution of cyclic freeze-thaw damage. Moreover, the conductance signatures driven by d 31 and d 33 modes were analyzed, respectively. It was found that the variation in the d 31 mode-dominated signal well agreed with the progressive damage characterized by the flexural strength degradation. The key innovation of this study is that a deep hybrid neural network DenseNet–GRU was constructed and well trained to predict the cyclic freeze-thaw damage from augmented EMI data. The results indicated that the proposed model achieved excellent performance with determination coefficients exceeding 0.997 for both bending scenarios. Additionally, DenseNet–GRU outperformed conventional baseline machine or deep learning models in prediction accuracy and noise-resistance capacity. Notably, it demonstrated good adaptability when trained with limited data samples. In summary, the proposed methodology enabled automated detection and accurate forecasting of the cyclic freeze-thaw damage in lining concrete without hand-crafted features.
... It has been found [10] that aggregate shape has a more significant effect on the mechanical properties and crack patterns of concrete. Among the meso-numerical concrete models, the common ones include the transition motor method [10], which regards the interfacial transition zone as high-porosity mortar and implements the corresponding equivalent deduction of mechanical parameters; the interfacial spring element method [11,12], which characterizes the mechanical behavior of the interfacial transition zone by establishing the spring with the multiple node pairs at the same node position from the junction between aggregate and mortar elements; the cohesive element method [13,14], which finds all element pairs sharing the same two nodes in the interfacial transition zone elements and mortar elements of the model and embeds cohesive elements to simulate concrete fracture. ...
... After 100 FTC, the water absorption of concrete increased by 65.85-270.73% due to increased microcracks generated within the concrete as a result of cyclic freeze-thaw (Gonen et al. 2014;Yijia et al. 2018). After 10 FTC, the ice pressure within the soil pores causes an increase in the degree of separation of the soil particles, resulting in more macropores with more water storage space, and an increased ability to absorb water (Hotineanu et al. 2015). ...
In this paper, the effects of freeze-thaw cycle (FTC), freezing temperature (FT) and initial moisture content (IMC) on Cunninghamialanceolata’s water absorption behavior were investigated. The porosity was measured with a gas permeability-porosity analyzer, and its tracheid structure changes were obtained using an optical microscope to explore microstructural deformation under varied freeze-thaw conditions. The results showed a maximum increase in water absorption and mean absorption rate of 25.2% and 24.8%, after 30 FTC experiments. The FTC experiments revealed a positive correlation between FTC and both water absorption and mean absorption rate. The FT experiments showed that Cunninghamia lanceolata’s water absorption and mean absorption rate initially increased, then decreased, and increased again with decreasing temperature, due to the tracheid volume change through icing ratio and ice crystal volume alteration. IMC experiments show water absorption and mean absorption rate decrease for cCunninghamia lanceolata with IMC 0-45% and increase for IMC 60-110% post freeze-thaw. The water absorption and mean absorption rate data were fitted to tracheid volume to derive the predictive models. Correlation analysis identifies the strongest impact of IMC on water absorption and mean absorption rate. FTC primarily influenced tracheal volume, while FT had the weakest effect on tracheal volume, water absorption, and mean absorption rate.
... Recent studies [11][12][13][14][15] have also shown that UHPC is an excellent 55 repair material. UHPC was first used in repairing NC in bridge deck systems [16], with 56 experiments confirming its ability to improve repair interface performance. Feng et al. 57 [17] compared NC-UHPC's repair effectiveness using circumferential confinement and 58 discovered that UHPC can create a denser and stronger OTZ, enhancing adhesive 59 performance. ...
In the harsh environment of extreme salt-freezing conditions, concrete structures face secondary durability issues after undergoing repairs, making it a critical yet challenging topic. This paper employs a novel ex-situ X-ray computed tomography approach to explore the mechanism of damage evolution in NC-UHPC composites under salt-freezing conditions. For the first time, we consider evolution in both external and internal pores to quantitatively assess the damage. Additionally, slant shear tests, Mercury Intrusion Porosimetry (MIP) were also employed to validate the damage mechanism of NC-UHPC. Finally, empirical formulas summarizing the bond strength and pore changes in NC-UHPC were derived. The results reveal a crucial factor influencing the progression of damage in the NC-UHPC composite: the presence of external pores that directly interact with the salty solution. Damage initiation primarily occurs within the NC-UHPC composite due to these external pores located in the NC region, subsequently extending into the OTZ and UHPC sections. Remarkably, the resistance of the OTZ, previously identified as the weakest zone in the NC-UHPC composite, surpasses that of the NC. This exceptional performance can be attributed to the higher porosity of the OTZ, offering additional space for the dissipation of pressure caused by freezing. What's even more important is that this highlights the consistent origin of damage in the NC-UHPC composite, emphasizing that it always begins within the NC. Considering this perspective prompts the question of whether the exceptionally high strength and durability of UHPC may lead to an excess of repair capabilities?
... Sulfate attack has been identified as a prominent factor contributing to the reduced durability of concrete [33,34], with documented cases of damage due to sulfate attack in coastal regions. Degradation of the mechanical properties of concrete due to freezethaw damage in civil engineering practice in cold climates is recognized as the primary factor [35,36]. Therefore, the development of high-performance concrete is of great importance in various engineering applications. ...
In this paper, firstly, the effects of graphene oxide on the mechanical properties of concrete were investigated. Secondly, the degradation and mechanism of the mechanical properties of graphene oxide concrete (GOC) under sulfate attack and a freeze–thaw environment were investigated. In addition, the dynamic modulus of elasticity (MOEdy) and uniaxial compressive strength (UCS) of the GOC were measured under different environmental conditions. According to the test results, the incorporation of graphene oxide in appropriate admixtures could improve the mechanical properties of concrete in these two working environments. It is worth noting that this effect is most pronounced when 0.05 wt% graphene oxide is incorporated. In the sulfate attack environment, the MOEdy and UTS of the GOC0.05% specimen at 120 cycles decreased by 22.28% and 24.23%, respectively, compared with the normal concrete specimens. In the freeze–thaw environment, the MOEdy and UTS of the GOC0.05% specimen at 90 cycles decreased by 13.96% and 7.58%, respectively, compared with the normal concrete specimens. The scanning electron microscope (SEM) analysis showed that graphene oxide could adjust the aggregation state of cement hydration products and its own reaction with some cement hydration crystals to form strong covalent bonds, thereby improving and enhancing the microstructure density.
... In cold regions, concrete structures are exposed to freeze-thaw cycle (FTC) environment, thereby degrading concrete's mechanical and fracture properties due to microstructural damage [27]. Freeze-thaw damage has a severe impact on the load-carrying capacity and durability of concrete structures. ...
To obtain the shear capacity calculation method and competition failure mechanism of headed stud connectors of steel-concrete composite structures under the influence of freeze-thaw cycles (FTCs) and artificial corrosion (AC), the material performance of concrete specimens after the FTCs and push-out tests of 36 headed stud connectors specimens were tested under the influence of FTCs and AC. The cubic compressive strength, dynamic elastic modulus, and mass loss rate of C50 concrete were obtained under different FTCs. Failure modes, load-slip curve, shear capacity, and shear stiffness of stud connectors were investigated based on push-out tests of miniaturized specimens. Based on the nonlinear fitting of test data, a formula for calculating the shear capacity reduction factor is proposed. Results show that the shear capacity and stiffness of stud connectors will deteriorate due to the deterioration of concrete performance caused by FTCs or the weakening of stud section caused by AC. The two failure modes of stud breakage or concrete cracking will change with the aggravation of FTCs and AC effect.
... In this section, the proposed DeepFEM is utilized to analyze the cohesive fracture process of notched beams in the three-point bending test. The cohesive zone model (Borg et al. 2004;Dong et al. 2018Dong et al. , 2021 has been widely used to study the fracture behavior of brittle or quasi-brittle materials, such as rock and concrete. Thus, the cohesive element is introduced in DeepFEM to capture the crack initiation and propagation process, in which the crack criterion is characterized by the strength, fracture energy, and softening law. ...
In this paper, an element-based deep learning approach named DeepFEM for solving nonlinear partial differential equations (PDEs) in solid mechanics is developed to reduce the number of sampling points required for training the deep neural network. Shape functions are introduced into deep learning to approximate the displacement field within the element. A general scheme for training the deep neural network based on derivatives computed from the shape functions is proposed. For the sake of demonstrations, the nonlinear vibration, nonlinear bending, and cohesive fracture problems are solved, and the results are compared with those from the existing methods to evaluate the performance of the present method. The results demonstrate that DeepFEM can effectively approximate the solution of the nonlinear mechanics problems with high accuracy, while the shape functions can significantly improve the computational efficiency. Moreover, with the trained DeepFEM model, the solutions of nonlinear problems with different geometric or material properties can be obtained instantly without retraining. Finally, the proposed DeepFEM is employed in the identification of material parameters of composite plate. The results show that the longitudinal and transverse elastic moduli of the ply in the composite plates can be accurately predicted based on the nonlinear mechanical response of plates.
... Therefore, obtaining the damage patterns of the microstructures during the deterioration process is crucial for a comprehensive understanding of the mechanical deterioration mechanisms. Many studies have investigated the damage evolution during FTC deterioration using either destructive or nondestructive test methods (Dong et al. 2018, Sokhansefat et al. 2020, Pilehvar et al. 2019. However, because the measurement of expansion or mechanical deterioration was not combined with that of the microstructural changes, the microscale damage and macroscale deterioration were not quantitatively related in these studies. ...
