Interfacial Transition Zone Research Articles

Mechanical properties and repairing mechanism of recycled cement stabilized macadam for road base based on microbial induced carbonate precipitation technology

The utilization of recycled coarse aggregate derived from construction and demolition waste (CDW) in the construction of road cement stabilized macadam base could effectively alleviate the shortage of natural sand and aggregate resources. To explore the repairing effect of microbial induced carbonate precipitation (MICP) on recycled cement stabilized macadam (RCSM), the physical, mechanical, and microscopic properties of recycled concrete aggregate under different precipitation precursor concentrations were researched in this paper. The mechanical properties of RCSM with varying contents of recycled concrete aggregate were analyzed before and after repairing. Based on scanning electron microscopy (SEM) and mercury intrusion porosimeter (MIP) tests, the microstructure and pore structure parameters of recycled concrete aggregate were explored, and the repair mechanism of MICP on RCSM was revealed via the performance analysis of recycled concrete aggregate and RCSM. The results show that MICP could effectively reduce the water absorption of recycled concrete aggregates, while simultaneously enhancing its apparent density and crushing resistance. In a certain range, the higher the concentration of the precipitation precursor, the better the repairing effect on the performances of recycled concrete aggregates. However, while the concentration of urea or calcium source concentration exceeding 1.0 mol/L, the activity of urease would start to be inhibited. The unconfined compressive strength of RCSM after MICP repairing could be increased by 22.7 % with a maximum extent compared with that before repair, while the maximum increase of indirect tension strength and flexural tensile strength was 15 % and 8.2 %, respectively. The biological CaCO3 generated by MICP reaction could fill the micro-cracks and pores of the recycled concrete aggregate efficaciously. Besides, it could also optimize the pore parameters and pore size distribution parameters, and enhance the adhesive strength of interfacial transition zone (ITZ) between cement and recycled concrete aggregates, which could improve the mechanical properties of RCSM.

The Inclusion and Initial Damage Inspection of Intelligent Cementitious Materials Containing Graphene Using Electrical Resistivity Tomography (ERT)

This paper examines the theoretical foundations of electrical resistivity tomography (ERT) technology, followed by the finite element analysis method, for the positive problem and the linear back-projection (LBP) procedure for the inverse problem. The conductivity distribution image of the modeled concrete is then reconstructed, which includes one circular aggregate and the surrounding mortar. It is discovered that the conductivity obtained can be used to find the inclusive aggregate, mortar, and interfacial transition zone (ITZ). Natural aggregate and mortar have conductivities of 0.046 ms/cm and 0.115 ms/cm, respectively. Additionally, the conductivity of the ITZ, which is always regarded as the initial damage, is about 0.081 ms/cm. ERT is a cost-effective and readily available technique for determining the initial distribution of the aggregate and related ITZ. Therefore, ERT is a promising tool for determining inclusions and initial damage in concrete.

Analytical Study on the Load-Bearing Performance of RC Beams Subjected to ASR Expansion

The alkali–silica reaction (ASR), a major cause of cracks in concrete, is a critical issue in the maintenance of social infrastructure. In this study, a concrete mesoscale model was meticulously developed, and a coupled stress–moisture model was also developed to reproduce ASR degradation. The aim was to investigate the effect of ASR degradation on the bending load-carrying capacity of RC beams. The concrete mesoscale model, specifically designed to reproduce ASR degradation, was modeled from three phases: coarse aggregate, mortar, and ITZ (interfacial transition zone). ASR was considered as the expansion of the coarse aggregate, and the objective was to reproduce expansion cracks with numerical analysis using the mesoscale model. Uniaxial compression tests were carried out on cylindrical specimens with ASR-accelerated deterioration to clarify the relationship between ASR deterioration and compressive properties, and the experimental results were used to identify material parameters in the mesoscale analysis model. The results showed that the model proposed in this study can reproduce the change in compressive properties due to expansion cracking. Finally, RC beams were constructed using the mesoscale model, and the effect of ASR degradation on the bending load-carrying capacity of the RC beams was investigated. The results showed that the presence of expansion cracks caused the initial stiffness of the load-displacement curves to decrease, but the bearing capacity tended to increase. This suggests that factors other than cracks, such as chemical prestress and boundary conditions in this model, have a strong influence on the load-bearing capacity of deteriorated RC beams.

Effect of modifiers on the properties of bamboo scraps/magnesium oxychloride composites under dry-wet cycling environments

Bamboo scraps/magnesium oxychloride composites (BS/MOC) is a new low-carbon and eco-friendly building material, which is composed of magnesium oxychloride cement (MOC) as the matrix and bamboo scraps as the reinforcing materials. However, the poor strength and durability of BS/MOC under special environmental conditions seriously restrict its application range. To solve the above problems, citric acid (CA), D-gluconic acid sodium salt (GS), and styrene-acrylate emulsion (SAE) were used as modifiers to improve BS/MOC properties. The effect of modifier addition on the mechanical strength and durability of BS/MOC was investigated under dry-wet cycling environments. The phase composition, microstructure, pore structure, and Clˉ concentration of BS/MOC were characterized by XRD, TGA, SEM, MIP, and ICS-600. The results showed that CA and GS improved the interface adhesion between bamboo scraps and MOC matrix, and both inhibited the hydration reaction of the residual MgO and the hydrolysis of phase 5 crystals, resulting in good mechanical properties and microstructural stability of BS/MOC under dry-wet cycles. GS outperformed CA in refining pore structure, improving mechanical properties and durability of BS/MOC under identical dry-wet cycles. Conversely, the addition of SAE increased initial defects and interfacial transition zones in the BS/MOC matrix, and increased the total porosity and the harmful pores content, which negatively affected the mechanical properties and durability of BS/MOC.

Mechanical properties and enhancement mechanism of iron ore tailings as aggregate for manufacturing ultra-high performance geopolymer concrete

Reusing of iron ore tailings (IOT), particularly as recycled aggregate to prepare concrete, plays an important role in reducing dependence on natural resources and solving the problem of waste accumulation. In this paper, the effects of IOT as aggregate on the flowability, compressive strength of ultra-high performance geopolymer concrete (UHPGC) were studied, and the enhancement mechanism of IOT on compressive strength was elucidated through microscopic characterizations. The results show that with the increase of IOT content, the flowability of UHPGC decreases, and the compressive strength increases first and then decreases. 25 % IOT replacement yielded the best compressive strength, and 50 % substitution of IOT was comparable to the without IOT regarding compressive strength. The microstructure analysis shows that the crystalline components in the IOT do not participate in the hydration reaction and have the effect of micro-aggregate filling. The amorphous components on the IOT dissolve rapidly in the early stage, participate in geological polymerization reaction, and produce synergistic effect with slag to promote the formation of hydration products. However, excessive IOT incorporation will inhibit the dissolution of slag active ions and hinder the formation of hydration products. In addition, the enhanced interfacial transition zone (ITZ) and mechanical interlocking effect formed by IOT can effectively inhibit the crack development of UHPGC.

Utilization of recycled fine aggregate in ultra-high performance concrete: Mechanical strength, microstructure and environment impacts

Recycled aggregate derived from construction and demolition (C&D) waste offers new opportunities for the construction industry due to the shortage of natural aggregate. This study presents the feasibility of utilizing recycled fine aggregate (RFA) in ultra-high performance concrete (UHPC) to alleviate autogenous shrinkage, mitigate environmental effects, and further improve mechanical strengths. Three types of RFA with different particle sizes (0–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm) are pre-saturated and then used as substitutes for quartz sand in UHPC. The influences of pre-saturated RFA on the workability, internal relative humidity, autogenous shrinkage, compressive strength, resistance to chloride ion penetration, and microstructure of UHPC are investigated. Experimental results showed that, compared to the plain UHPC, incorporation of 20 % RFA with particle size of 1.18–2.36 mm provides efficient internal curing, maintaining a higher internal relative humidity, and thus reducing autogenous shrinkage by 78.5 % at the age of 7 days. The compressive strengths of the UHPC containing 20 % RFA with particle size of 1.18–2.36 mm shows 7.1 % increase at the ages of 28 days. While it has a negligible effect on the fluidity and resistance to chloride penetration. The underlying mechanisms for the enhancement of properties involve the improved hydration degree of UHPC due to internal curing, which optimizes the structure of the interface transition zone and reduces the number of large pores. Furthermore, the sustainability analysis indicated that the use of RFA in UHPC exhibits 7.0 % lower carbon emissions and 7.8 % lower energy consumption, respectively. This study successfully proposes an effective approach for mitigating the autogenous shrinkage of UHPC without sacrificing strengths.

Study on the mechanical properties of recycled brick coarse aggregate concrete based on finite element modeling

In recent years, the use of recycled materials in concrete production has garnered significant attention due to their environmental and economic benefits. To promote the application of recycled aggregates, this study focuses on investigating the utilization of Recycled Brick Coarse Aggregate (RBCA) as a substitute for natural aggregate. This paper presents the development of stochastic convex polygonal RBCA through the utilization of a custom-programmed algorithm and proposes a finite element model designed to simulate the behavior of RBCA concrete under compression and splitting tensile. Numerical simulations were conducted to investigate the effects of brick aggregate Replacement Rate (RR) and porosity on the compressive and splitting tensile properties of RBCA concrete. A strong correlation was found between the Concrete Damage Plasticity (CDP) model developed in this study and experimental results, indicating high reliability. The results indicate that the replacement rate of brick aggregates has a more significant impact on the compressive strength than on the splitting tensile strength of concrete. Furthermore, the distribution of coarse aggregates and pores has a minor influence on the mechanical properties and ultimate failure mode of RBCA concrete but significantly affects the crack distribution pattern. The sequence of damage initiation in RBCA concrete was found to be: pores, old Interfacial Transition Zone (ITZ), old mortar, new ITZ, new mortar, RBCA, and Natural Coarse Aggregate (NCA). These findings contribute to a comprehensive understanding of RBCA's performance and offer valuable insights for optimizing its behavior.

Fracture mechanical properties and interfacial characteristics of engineered cementitious composites containing coarse aggregate

Engineered cementitious composites (ECC) have significantly high deformability, but their application in the field of engineered crack prevention is severely limited by their high shrinkage and high cost. To address this issue, a safer and more economical ECC was designed in this paper by adding coarse aggregate (CA) into the ECC matrix (i.e., ECC-CA). Then, experimental studies on the fracture properties of ECC-CA were carried out from both macroscopic and microscopic perspectives, by considering four CA mass contents and three CA particle sizes. The results show that ECC-CA maintains good mechanical properties and deformation capacity as ECC. Its crack mouth opening displacement corresponding to the largest particle size (13–17 mm) and the largest mass content (30 %) is equivalent to 47.8 % of that of ECC, which is about 40 times higher than that of conventional concrete. Further, the interfacial transition zone characteristics between each phase medium and matrix were analyzed in ECC-CA for the purpose of clarifying the crack initiation and evolution trends, elucidating the influence of CA on the fracture mechanism of ECC-CA (i.e., fiber cage effect) based on both macroscopic performance and microscopic characteristics.

Ultrasonic wave characteristics in multiscale cementitious materials at different stages of hydration

Monitoring the microstructural change in cementitious materials during hydration is an essential but challenging task. Therefore, a non-invasive and sophisticated technique is warranted to understand the microscopic behaviour of the multiphase cementitious materials (where the length scale of the constituents varies from centimeters to micrometers) in different stages of hydration. Due to exothermic hydration reactions, different hydration products start to evolve with individual mechanical properties. In concrete, an interface transition zone (ITZ) appears between the aggregate surface and paste matrix, which influences the overall properties of concrete material. In the present research, 1) several wave characteristics, such as wave velocity, energy distribution, and signal phase are found out using Ultrasonic Pulse Velocity (UPV), Wavelet Packet Energy (WPE) and Hilbert Transform (HT) methods, to monitor the hydration mechanism (1d-28d) in cement-based materials with two levels of heterogeneities (cement paste and concrete, representing microscale and mesoscale, respectively). Also, the unique nonlinear behaviour is studied in the frequency domain using the promising Sideband Energy Ratio (SER) and Sideband Peak Count Index (SPC-I) methods. 2) Numerical simulations are carried out to understand the wave interaction in the developing microstructure. A discretized microstructure of cement shows microscopic details of each phase at any instant of hydration (e.g., formation stage and after complete maturity level). The experimental and numerical investigations on the characteristics of the nonlinear ultrasonic wave propagation show the impact of microstructural development of multi-scale cementitious materials during hydration.

Chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion stability of interfacial transition zone material using alkali-treated banana fiber for concrete

ABSTRACT It might be of interest for authors to learn more that in the early 1900s, fibers were used in cement-based material, as cement-based materials exhibit shrinkage cracking over time, which can be controlled by adding fibers. The main aim of the inserting natural fiber into cement-based material is to decrease the shrinkage of cement-based material, prevent the rising of shrinkage cracks, and develop low-cracking cement-based material. In the research, the same aim aforementioned was kept same way. For carrying out the aim, agricultural waste, known as banana fiber (BF), can be considered a shrinkage reducer, expansion stabilization, a renewable material and has potential to make cement-based material transformed into a green construction material. This research investigated the effect of BF incorporation on cement paste shrinkage. Thus, five mixes were developed with different BF additions based on the total volume of cement paste (0, 0.5, 1, 1.5 and 2%). For each mixture, four tests were carried out to assess the impact of BF addition on the paste’s volume stability: chemical, autogenous, drying shrinkage and expansion. Testing was conducted for up to 90 days. Compared to the control mix, the addition of 2% BF reduced chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion by 27%, 57%, 47%, and 66%, respectively. Furthermore, a positive correlation was observed between chemical shrinkage and both autogenous and drying shrinkage and the percentage of BF content. Conversely, there was an inverse relationship between chemical shrinkage and expansion. The most significant conclusion to emerge from this study is that the incorporation of banana fiber (BF) into alkali-treated concrete results in a reduction in chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion. This is attributed to the molecular structure of BF, which is characterized by uninterrupted glycosidic linkages, leading to alkaline breakdown within the alkaline environment. Consequently, the alkali-treated BF can be described as a volume stability admixture in concrete technology.

Micromechanical and chemical characteristics of interfacial transition zone in alkali-activated slag concrete containing lightweight iron-rich aggregates

This study explored the time-varying alkali-activation effects of the lightweight aggregates (LWA) on the interfacial transition zone (ITZ) of the alkali-activated slag concrete with different curing ages, molar ratios, and alkali concentrations from 28 to 300 d. The improved micromechanical performance of the ITZ at 28 d stemmed from the early-age internal curing effect of the porous LWA. However, the post-28 d internal curing effect diminished, with the alkali-activation dominating the performance of the ITZ from 28 to 300 d. Although alkali-activated cement possessed early strength characteristics, the deconvolved phase results illustrated that alkali activation persisted in the ITZ between the LWA and cement from 28 to 300 d, leading to a high proportion of calcium silica aluminate hydrate. As a marker, Fe from the lightweight iron-rich aggregates mitigated into the alkali-activated cement, demonstrating the alkali-activated reaction between the LWA and alkali-activated slag matrix. Molecular dynamics simulations further characterized that the low content of Fe did not decrease the overall strength of the ITZ. The interfacial interaction energy revealed the alkali-activation between the LWA and cement compensated for the weakening of mechanical properties caused by Fe ions on the ITZ.

Investigating the Influence of Oil Shale Ash and Basalt Composite Fibres on the Interfacial Transition Zone in Concrete

Investigating the Influence of Oil Shale Ash and Basalt Composite Fibres on the Interfacial Transition Zone in Concrete

Uncertainties quantification for damage localization in concrete based on Bayesian method

The presence of defects in concrete can diminish load-bearing capacity of structures, giving rise to potential concerns regarding safety and durability. Thus, a method that enhances the sensitivity, resolution and robustness of damage localization is critically necessary to assess the condition of concrete structures. This research presents a damage localization method based on Bayesian probabilistic fusion, and uncertainties from measurement and identification process are considered and quantified. The likelihood function is constructed based on the hyperbola-based damage localization method, and the posterior distributions of unknown parameters are calculated via Bayesian theorem combined with measurement data. Furthermore, a meso-level finite element model is established, wherein the concrete medium is considered as a three-phase composite material consisting of polygonal aggregates, mortar matrix and interface transition zones. Owing to the meso-level modeling, the propagation behavior of stress waves within concrete and complicated interactions between stress waves and concrete internal structures can be better characterized. Finally, the damage information, time-difference-of arrival, is extracted from the response signals and the efficiency of the proposed method is verified numerically. The numerical results demonstrate that the proposed probabilistic fusion method outperforms the conventional hyperbola-based method in terms of achieving high spatial resolution and resilience in damage localization.

Elastoplastic damage model and numerical implementation of nano‐silica incorporated concrete

AbstractAn energy‐based isotropic elastoplastic damage model is developed for investigating the elastoplastic damage responses and stress–strain relationships of nano‐silica incorporated concrete. The formulation employs a multiscale micromechanical framework to determine the effective elastic properties of composites at different scales. The stress–strain constitutive relation is derived by splitting the strain tensor into “elastic‐damage” and “plastic‐damage” parts while introducing the homogenized free potential energy function and the undamaged potential energy function. The elastoplastic damage response of the material is further characterized by elastic–plastic‐damage coupling. To construct realistic 3D three‐phase concrete mesostructures in numerical simulations, this paper introduces an encapsulation placement method that avoids particle overlap checking when placing aggregates. This methodology allows adjustments for the aggregate compactness as needed and enhances computational efficiency in concrete mesostructure construction. The numerical results of the modeling show good agreement with the experimental values in the open literature. Further, the influence of nano‐silica addition contents and ITZ (interfacial transition zone) thicknesses on the elastoplastic damage response of nano‐silica incorporated concrete are quantitatively and qualitatively investigated for the optimization of nano‐silica incorporated cementitious composites. The proposed model facilitates simulating and optimizing the mechanical characteristics of nano‐silica incorporated concrete and enhances the computational efficiency of 3D concrete modeling with the introduced encapsulation placement method.

Enhancement of the tensile properties of cement mortar composites with nanoadditives produced by chemical vapor deposition

While graphene effectively enhances the performance of cement-based materials, its current production methods are characterized by environmental unfriendliness and high energy consumption. To investigate a large-scale and eco-friendly graphene preparation approach, Carbon Nano Sheets (CNS) were synthesized via chemical vapor deposition (CVD). The influence of CNS content on the tensile strength of cement mortar was assessed through the Brazilian splitting test. Concurrently, the mechanism of CNS was examined using acoustic emission monitoring and scanning electron microscope. The experimental results revealed that methane can be effectively decomposed into high-quality CNS at 1080 ℃ when using fly ash, silica fume, and sand as substrates. The Brazilian splitting test revealed that CNS effectively enhances the tensile strength of cement mortar, with improvements ranging from 9 % to 58.7 %. Acoustic emission results indicated that the inclusion of CNS reduces the occurrence of micro-fractures during the failure of cement mortar specimens. Furthermore, nano-mechanical testing and microstructural characterization demonstrate that CNS can reduce micro-cracks and pores in the interface transition zone and hydration products, playing a role in dense hydration products. Furthermore, it can decrease the width of the interface transition zone and enhance the micro-mechanical properties of cement pastes. This study offers a novel approach for the eco-friendly production of cement nano additives.

Investigating specimen size and shape effects on compressive mechanical behaviors of recycled aggregate concrete using discrete element mesoscale modeling

In comparison to natural aggregate concrete (NAC), recycled aggregate concrete (RAC) typically exhibits a more diverse composition of materials, heightened variability and greater inherent weaknesses. These characteristics may result in varying effects of specimen size and shape on compressive responses. Within this framework, the present study endeavors to comprehensively investigate these influences on RAC's compressive properties and their underlying mechanisms utilizing discrete element simulation technology. At the mesoscale, RAC is depicted by several components, encompassing both new and old aggregates, mortar and interfacial transition zones. Through integrating contacts for each phase, elucidating mesoscale mechanical responses with a parallel bond model and introducing Weibull random fields to delineate variations in phase properties, this study effectively simulates these mechanical responses. Subsequent extensive calculations scrutinize the repercussions of specimen size and shape on the compressive strength, elastic modulus, peak strain and failure modes of RAC across varying water-to-binder ratios. The study concludes that RAC manifests a size effect, albeit less pronounced than in NAC with an equivalent water-to-cement ratio, yet more significant than in mortar. Moreover, owing to end plate constraints, the reduction in RAC's cubic compressive strength is notably less than its prismatic compressive strength. Based on these findings, it is recommended to establish the strength size reduction coefficient and cube-to-cylinder shape coefficient for RAC at 0.86 and 0.72, respectively. Notably, these values diverge significantly from the respective 0.81 and 0.78 coefficients for NAC.

Numerical Study of Concrete: A Mesoscopic Scale Simulation Methodology

This study aims to understand and simulate the mechanical properties of concrete, focusing specifically on the mesoscopic scale and its relation to the macro scale. Investigating concrete at this level involves examining its composition as a heterogeneous amalgamation of mortar, aggregates, and the Interfacial Transition Zone (ITZ). Numerical models, utilizing the finite element method (FEM), are employed to thoroughly examine the structural behavior of concrete. The study uses MATLAB (2023a) programming to develop three-dimensional models, which are then subjected to FEM analysis. Various mesoscopic Representative Volume Elements (RVEs) are formulated, considering spherical aggregates with different locations and dimensions to capture the complex nature of concrete. MATLAB is used to generate files containing comprehensive information about the RVEs, which are then processed with FEM to simulate compression strength tests. As the complexity increases with the inclusion of the ITZ, prismatic RVEs are developed to better represent real-world conditions. The proposed mesoscopic model establishes a foundational framework for a numerical simulation methodology tailored to laboratory compression tests, bridging the gap between mesoscopic and macroscopic scales. This approach provides detailed insights into concrete behavior, elucidating deformation and fracture mechanisms. Although not a complete substitute for experimental methods, these models offer a cost-effective and efficient alternative, identifying vulnerable areas and exploring the effects of additional materials on concrete behavior. The progressive replacement of laboratory tests with numerical simulations using RVEs of specific compositions will make the study of concrete behavior at the mesoscopic scale increasingly sustainable, paving the way for more efficient and environmentally friendly research practices in the field.

A novel cement-based interface functional material for application onto shotcrete-rock interface of tunnel in cold regions

In cold regions, the “natural weak zone”+“frost heave cracking” problems at the interface between shotcrete and rock will superimpose damage to the shotcrete-surrounding rock support system structure. However, there is no direct and effective technique to improve the bond strength and frost resistance of shotcrete for infrastructure such as tunnels in cold regions. Based on this, this study innovatively proposes the pretreatment technology of the interface between shotcrete and surrounding rock in tunnels in cold regions, and tries to investigate the fracture evolution of the binary and the distribution characteristics of the interface transition zone (ITZ) in cold regions under the action of interface functional material (IFM) by relying on the techniques of mechanical strength test, morphology analysis, and microstructure test. The study showed that: (1) the optimal mix ratio of IFM was designed as cement (10)+water (4)+calcium acrylate(1.5 %)+bamboo liquefied binder (4 %)+acrylate laminating adhesive (8 %)+ICA (2 %). At room temperature, the shear strength of the binary sample pretreated with the IFM was elevated by 1.56 MPa compared with that of the normal sample, and this increase could be raised to 1.64 MPa under freeze-thaw cycles (FTC). (2) As the freeze-thaw effect intensifies, the number of sandstone particles adhering to the failure surface of the binary increases correspondingly, and the morphology of the failure surface also becomes more undulating. This is due to the fact that after a certain FTC, more cracks are deflected towards the sandstone side due to the higher degradation of the sandstone compared to the ITZ. (3) Under FTC, the application of IFM will lead to an increase in the proportion of sandstone adhering to the failure surface and the fractal dimension of the failure surface, and this phenomenon becomes more pronounced with the intensification of FTC. (4) In the ITZ space, the hydration products and pore structure of the area closer to the sandstone are worse, the use of IFM can optimize this phenomenon. The new idea of utilizing the surrounding rock surface pretreatment technology to improve the bond strength and frost resistance of shotcrete proposed in this study has good application prospects in the construction of tunnels and other infrastructures in cold regions.

Bonding performance of ethylene vinyl acetate reinforced carbon nanotube repair materials

Inorganic repair materials have significant advantages such as high durability, high strength, and good corrosion resistance. However, their low bonding strength and inadequate tensile performance are clear disadvantages, which often results in problems like cracking, delamination, and insufficient repairing strength. In the current study, a new repair material is developed, which enhances the interfacial bonding performance of carbon nanotubes (CNTs) repair materials by introducing ethylene vinyl acetate (EVA). The bonding strength of composite specimens was tested by splitting tensile test. Then the microstructure analysis of the repaired materials was conducted by X-ray computed tomography, backscattered electron imaging, and scanning electron microscopy. The phase composition of the repair material was further analyzed by Fourier transform infrared spectroscopy. Finally, the bonding mechanisms of EVA reinforced CNTs repair materials were discussed. The results indicate that the interaction between EVA and CNTs can enhance the bonding performance of repair materials. Additionally, the polymer film formed by EVA within the repair material can refine the pores, thereby reducing the porosity of the interfacial transition zone and that of repair materials. The electrostatic repulsion between EVA and CNTs contributes to the uniform dispersion of CNTs within repair materials.

Unraveling concrete's interfacial transition zone vulnerability under erosive environments: A molecular dynamics study

The Interfacial Transition Zone (ITZ) in concrete is considered to be the weakest region of the mechanical properties of concrete, owing to the prevalence of microcracks induced by various external factors. These microcracks facilitate the ingress of corrosive solution into the ITZ through pores or crevices, ultimately impacting its mechanical integrity. This study aims to investigate the effects of different erosive environments on the mechanical properties of concrete ITZ and to analyze the intrinsic weakening mechanism via molecular dynamics simulations. The effects of different water contents and different ionic solutions are individually discussed in this study. Simulation results demonstrate a distinct trend in the mechanical properties of ITZ, exhibiting an initial increase followed by a decrease with the rise of water content under various conditions. Moreover, the magnitude of the mechanical properties of ITZ exhibits a hierarchy under different ionic solution conditions, ranked as follows: dry >10 wt% Na2SO4+NaCl >5 wt% Na2SO4 > 5 wt% NaCl >5 wt% Na2SO4+NaCl > H2O. The mechanical properties of ITZ are significantly influenced by its internal chemical bonds, which are susceptible to erosion from the infiltrating solution, resulting in the rupture of original chemical bonds and consequent reduction in ITZ's mechanical strength.