Properties Of Interfacial Transition Zone Research Articles

Mechanical behavior of ultra-high performance concrete (UHPC) using recycled fine aggregate cured under different conditions and the mechanism based on integrated microstructural parameters

Mechanical behavior of ultra-high performance concrete (UHPC) using recycled fine aggregate (RFA) was experimentally investigated. It was found that the compressive and flexural strength and tenacity of UHPC decreased as more RFA was introduced, but were enhanced by the autoclaved curing. The total length of the diverse types of interfacial transition zones (ITZs) was found to increase along with the growth of RFA replacement ratios; the quality of ITZs was improved by the autoclaved curing. This paper integrated the geometric and mechanical properties of ITZs and the other material phases on the micro scale to propose two ITZ parameters, ψ1, ψ2, and a more comprehensive microstructural parameter, ψ3. Based on correlation analysis, ψ3 was proved to be more reliable in describing the key microstructural features of UHPC prepared with RFA, and also in quantitatively revealing the mechanism for the mechanical behaviour of UHPC on the macro scale, regardless of the RFA dosages or curing conditions.

Investigation on degradation of micromechanical properties of interfacial transition zone of ultra-high performance concrete under freeze-thaw cycles

In order to explore frost resistance mechanism of ultra-high performance concrete (UHPC) under freeze-thaw (F-T) action, the microstructures and micromechanical properties of two interfacial transition zones (ITZ) of steel fiber-paste and fine sand-paste are investigated using nanoindentation technology. The experimental results demonstrates that there exits an obvious weak zone in the ITZ of fiber-paste, of which the microstructure is largely affected by F-T action. The relative variation of the amplitude of modulus and hardness of calcium silicate and calcium hydroxide is less than 0.2 under F-T action. The volume fraction of micropores increases exponentially as the increase of F-T cycles, and the pore size gradually extends to tens of microns. The thickness of ITZ between steel fibers and paste gradually increased from 20 to 65 μm after 0–1500 F-T cycles. Thus, the volume fraction of micropores and the thickness of ITZ in steel fibers can be used to effectively characterize the degradation of micromechanical properties of UHPC under cold climates.

An investigation into the impact of warm mix asphalt additives on asphalt mixture phases through a nano-mechanical approach

This paper presents the results of a novel investigation to evaluate the effect of Sasobit, Rediset WMX and Rediset LQ on the mechanical properties of asphalt mixture phases, aggregate, interfacial transition zone (ITZ) and mastic using Nanoindentation. All warm additives improved the nano-mechanical properties of the ITZ if the reduction in the production temperature was not more than 10 °C for an asphalt mixture with the 40/60 hard binder and 20 °C with the 100/150 binder. The nano-mechanical properties of mastic for all WMAs manufactured at 20 °C lower than the control using 40/60 mix were less than the control mix. However, as the reduction in the production temperature decreased to 10 °C, the modulus and hardness of the mastic and ITZ for all WMAs significantly increased. While, 20 °C reduction in the production temperatures was achieved using 100/150 with inclusion of warm additives and the values of nano-mechanical properties of ITZ and mastic was same or even higher than the control mix. It can therefore be concluded that, in order to produce a warm asphalt mixture that performs the same or even better than the traditional HMA, the effect of production temperature must be addressed. In summary, Nanoindentation provides new insight about the effect of warm additives on the nano-mechanical properties of asphalt mixture phases and predicts level of bonding between aggregate and binder.

Evaluation of morphology and size of cracks of the Interfacial Transition Zone (ITZ) in concrete containing fly ash (FA)

Interfacial Transition Zone (ITZ) of coarse aggregate cement matrix is commonly regarded as the weakest element of concrete. In this phase – the first cracks in the material are initiated, and the process of destruction of the composite begins.An improvement of the ITZ properties are positively influenced by the mineral additives used for the composite. One of such a substitute for a binder is, potentially hazardous industrial waste, siliceous fly ash (FA).In this paper the ITZ between aggregate and cement paste in concretes containing FA is considered. The paper presents the results of tests on the effect of the addition of FA in the amount of: 0, 20 and 30% by weight of cement on morphology and size of cracks of the ITZ in composites.In matured concretes the smallest cracks occur in composite with the 20% FA additive. It can be concluded that composites with 20% addition of FA are characterized by low permeability and therefore high durability.The results of tests carried out can be helpful in obtaining concrete with the highest possible: strength, durability and reliability of operation. Moreover, such procedures also cause a restriction storage of hazardous materials, i.e. FA – by 160 million tons per year.

A multiphase numerical simulation of chloride ions diffusion in concrete using electron microprobe analysis for characterizing properties of ITZ

In order to demonstrate the chlorides ions diffusion in concrete, a multi-phase numerical model was established at mesoscale. The thickness of interfacial transition zone (ITZ) surrounding aggregate was measured based on an element analysis using electron probe technique. And the diffusivities of ITZ and mortar matrix were deduced through a one-dimensional transmission test. By introducing the experiment parameters into the two-dimensional numerical model, the chloride ions diffusion in concrete was simulated and verified through the electron probe technique accordingly. A sensitivity analysis on the parameters was conducted to furtherly assess the influence ITZ on the chloride ions diffusion in concrete. This study indicates that the size of coarse aggregate has no influence on the thickness of ITZ which follows a normal distribution. The properties of ITZ, including its the thickness and diffusivity, have significant affections on the diffusion of chlorides ions in concrete. And for the concrete employed in this research, the diffusivity affects the diffusion more severely than thickness of ITZ.

A theoretical method to determine the tortuous crack length and the mechanical parameters of concrete in direct tension—A particle size effect analysis

Cementitious materials, mainly in the form of concrete, belong to a class of macroscopically heterogeneous materials. The building technology of mass concrete structures enables large-sized coarse aggregate to be used. The maximum coarse aggregate size, in conjunction with the mechanical properties of the interfacial transition zone (ITZ), have great influences on the mesoscopic crack path and the macroscopic mechanical behavior of concrete. Herein this study, based on some pioneering work (Stroeven, 2000; Rosselló and Elices, 2004, Rosselló et al., 2006; Elices and Rocco, 2008), the effects of varying the maximum coarse aggregate size and the ITZ strength on the global mechanical properties of concrete in direct tension are theoretically modelled from a mesoscopic point of view. The particle size effect behavior of concrete is analyzed based on the proposed theoretical method, and some general conclusions can be drawn as: (1) The degree of tortuosity of the mesoscopic crack path in direct tension increases with increasing maximum coarse aggregate size and with decreasing ITZ strength; (2) The fracture energy and the tensile strength of concrete increase dramatically with increasing ITZ strength; (3) For normal strength concrete, the fracture energy and the tensile strength decrease with increasing maximum coarse aggregate size, while for relatively high strength concrete, the trends are the opposite; (4) The properties of ITZ could significantly affect the homogeneity of concrete. High quality ITZ could make the mechanical properties of concrete more homogeneous and get a relatively high strength concrete, consequently a short characteristic length and a high brittleness number are resulted; (5) For normal strength concrete, the characteristic length increases with increasing maximum coarse aggregate size, while for relatively high strength concrete, it is fairly insensitive to the maximum coarse aggregate size. It is hoped that this theoretical method may be helpful in the study of size effect and in the design of concrete and future cementitious materials.

Micromechanical performance of interfacial transition zone in fiber-reinforced cement matrix

The paper investigates microstructure, chemical composition and micromechanical behavior of an interfacial transition zone (ITZ) in steel fiber reinforced cement matrix. For this goal, a combination of scanning electron microscopy (SEM), nanoindentation and elastic homogenization theory are used. The investigated sample of cement paste with dispersed reinforcement consists of cement CEM I 42,5R and a steel fiber TriTreg 50 mm. The microscopy revealed smaller portion of clinkers and larger porosity in the ITZ. Nanoindentation delivered decreased elastic modulus in comparison with cement bulk (67%) and the width of ITZ (∼ 40 μm). The measured properties served as input parameters for a simple two-scale model for elastic properties of the composite. Although, no major influence of ITZ properties on the composite elastic behavior was found, the findings about the ITZ reduced properties and its size can serve as input to other microstructural fracture based models.

Quantitative characterization and elastic properties of interfacial transition zone around coarse aggregate in concrete

Backscattered electron images (BSE) obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone (ITZ) in concrete. Influences of aggregate size (5, 10, 20, and 30 mm), water to cement ratio (0.23, 0.35 and 0.53) and curing time (from 3d to 90d) on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu & Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.

Properties of recycled aggregate concrete with different water control methods

The paper studies the properties of Recycled Aggregate Concrete (RAC) with four different water control methods: the control group, pre-wetting with the same total water amount group, pre-wetting with the same mixing water amount group and adding extra mixing water group. Macro properties of concrete materials, i.e., compressive strength, drying shrinkage and chloride penetrability, and micro properties of Interfacial Transition Zone (ITZ), i.e., length and elastic modulus, are tested. The results show that RAC with a pre-wetting process has lower compressive strength and a higher Cl− diffusion coefficient, but a smaller shrinkage value compared to RAC with the same total water amount and no pre-wetting process. Adding extra mixing water process weakens the properties of RAC. The comprehensive elastic modulus is defined as an integrated interface parameter, and it has a good correlation with the macro properties like compressive strength and diffusion coefficient of Cl− of RAC.

Properties of interfacial transition zones (ITZs) in concrete containing recycled mixed aggregate

Concretes containing mixed recycled aggregate (RA) have a larger number of coarse aggregate/paste interfacial transition zones (ITZs) than conventional concretes, due to the various component materials present in recycled aggregate. This study investigated the properties of various RA/paste ITZs in concrete using nanoindentation and scanning electron microscopy (SEM) and analysed the possible impact of the properties of the ITZs on the macro-mechanical performance of recycled concrete. It was found that the elastic modulus of the ITZ varies with the type of constituent materials present in recycled aggregate, with ITZs associated with organic components (e.g. wood, plastic and asphalt) exhibiting lower minimum elastic modulus values. The impact of ITZ properties on macro-mechanical properties of concrete depends on the relative content of different constituent materials present in the recycled aggregate and the micro-mechanical properties of the ITZs involved.

Nano-mechanical behavior of the interfacial transition zone between steel-polypropylene fiber and cement paste

The fiber-matrix interfacial transition zone (ITZ) at nanoscale plays an important role in determining the mechanical performance of hybrid steel-polypropylene fiber reinforced concrete at upper scales. This paper investigates the elastic behavior of the ITZ between steel/polypropylene fiber and pure cement paste through nanoindentation for different water/cement ratios. The microstructure mapping and gradient of ITZ were analyzed based on the elastic modulus (E) and hardness (H) distributions. The morphology of ITZs was observed with the help of Scanning Electron Microscope. In addition, to probe into the formation mechanism of ITZ, distinct phases in ITZ were statistically determined from the frequency density distributions of E and H values through the deconvolution technique. Results show that the thickness of fiber-matrix ITZ mainly depends on the fiber type, where the steel fiber and polypropylene fiber ITZ are about 30μm and 15μm in thickness respectively. It is also found from E distribution that a trough in the steel fiber ITZ exists at lower w/c ratios, whereas a gradual growth of E and H values is demonstrated away from polypropylene fiber surface for all cases shown. The ITZ’s chemical compositions at nanoscale suggest that the volume fractions of HD C-S-H, CH/C-S-H and porosity are noted to be the main determinants for the overall properties of ITZ. In comparison with steel fiber samples, a larger amount of porosity exists in the vicinity of polypropylene fiber surface. Finally, based on the test data, the ITZ formation mechanism was discussed with water/cement ratio effect considered.

Improved interfacial transition zone between aggregate-cementitious matrix by addition sugarcane industrial ash

The aim of this study was to evaluate the influence of sugarcane industrial ash (SCIA) on mechanical properties of interfacial transition zone (ITZ) between aggregates and cementitious matrix by nanoindentation technical analysis. The sugarcane biomass (agroindustrial by-product) was used for generation of electricity by burning in a cogeneration power system. The results of nanoindentation analyses showed that the ITZ thickness varied significantly with the water/binder ratio. Each formulation used different water and binder ratio, with the inclusion of 20% silica fume (SF) or SCIA. In fact, the mineral additions caused a reduction of the thickness of the matrix-aggregate ITZ, and consequently increased the values of the indentation modulus and hardness in relation to aggregate-matrix interface of the reference concrete.

ITZ properties of concrete with carbonated steel slag aggregate in salty freeze-thaw environment

The concrete samples with carbonated steel slag aggregate (CSA), normal aggregate (NA) and crushed steel slag aggregate (SSA) with W/C of 0.42 were prepared. The properties of the resistance on freezing and thawing were investigated and compared by freeze-thaw test with the condition of fresh-water and salt-water. The rapid chloride migration test (RCM) and coulomb electric flux test (CEF) were made in order to test the resistance of the concrete to chloride ion penetration. The ITZ properties and freeze thaw resistance of concrete were investigated by micro hardness tests, SEM, Ca/Si ratios, weight loss and relative dynamic elastic modulus test. The results show that using CSA instead of NA increased the freeze-thaw cycles from about 30 cycles to 175 cycles in salt-water condition and from about 150 cycles to 300 cycles in fresh-water condition. The average value of the hardness of ITZ around CSA is more than 43, which may due to the low W/C ratio caused by high water absorption of the CSA. The range of interfacial transition zone (ITZ) of CSA from SEM and EDS is larger but denser than NA and SSA, and fewer cracks are observed. The resistance to freeze and thaw will be improved by the hydration of steel slag to bond cement matrix. The cambered surfaces of CSA are less likely to occur stress concentration.

Influence of mesoscale three-phase parameters to the tensile behavior of concrete

In the mesoscopic level, concrete is regarded as three-phase composite material with cement matrix, aggregate, and the interfacial transition zone (ITZ) between them. The mechanical properties of ITZ are regarded weaker than those of the cement matrix and aggregate. In this study, a mesoscale mechanical model based on the interface specimen with a single aggregate is established to study the influence of three-phase parameters on the interface specimen under quasi-static and dynamic direct tensile loading. Besides, the loading rate effect is also considered in this study to further analyze the dynamic performance of ITZ and the whole interface specimen. According to the numerical results, it is indicated that the ITZ properties (elastic modulus and strength) play significant roles in the performance of the interface specimen under quasi-static direct tensile loading. However, the cement matrix is dominant to the mechanical properties of interface specimen under dynamic tensile loading. Moreover, the properties of ITZ (elastic modulus, strength, and DIF values) and the ITZ thickness have some influence on the dynamic performance of ITZ and the whole interface specimen under dynamic tensile loading. In contrast, the Poisson’s ratio and density of ITZ have little influence on the dynamic behavior of the whole interface specimen. Additionally, the aggregate diameter is influential to the time reaching peak stress of ITZ and the whole interface specimen, and the loading rate only influences the time to reach the peak stress of ITZ under dynamic tensile loading.

Multi-scale approach for modeling the transversely isotropic elastic properties of shale considering multi-inclusions and interfacial transition zone

Multiscale approach based explicit analytic predictions are obtained for the transversely isotropic properties of shale rock considering the multi-inclusion and interfacial transition zone (ITZ) effects. Representative volume elements (RVEs) are utilized to describe the material’s hierarchical microstructures from the nanoscale to the macroscale. A new multilevel micromechanical homogenization scheme is presented to quantitatively estimate the material’s transversely isotropic properties with the multi-inclusion and ITZ effects. The ITZ is characterized by the interphase material, whose effects are calculated by modifying the generalized self-consistent model. Furthermore, the explicit form solutions for the transversely isotropic properties are obtained by utilizing the Hill polarization tensor without numerical integration and the standard tensorial basis with the analytic inversions of fourth-rank tensors. To verify the proposed multiscale framework, predictions obtained via the proposed model are compared with experimental data and results estimated by the previous work, which show that the proposed multi-scaling approaches are capable of predicting the macroscopic behaviors of shale rocks with the multi-inclusion and ITZ effects. Finally, the influences of ITZ and inclusion properties on the material’s macroscopic properties are discussed based on the proposed multiscale framework.

Study on the Interfacial Transition Zones of Recycled Aggregate Concrete

Background/Objectives: The objective of the present paper is to study the effect of admixtures and the mixing approach on the Interfacial Transition Zone (ITZ) of Recycled Aggregate Concrete (RAC). Methods/Statistical analysis: The micro structure of RAC is generally analyzed by the Vickers micro-hardness test, Atomic-Force Microscopy (AFM), Nanoindentation and scanning electron microscope (SEM). The various mixing approaches were presented for partially and fully replacement of recycled aggregate (RA) which basically enhanced the properties of RA. It is also observed that the use of fly ash and silica fume improve the properties of ITZ. Findings: This paper presents a review of the studies on the micro structure and mixing approach of RAC elements and Structures. The behavior of RAC has been studied since last 45 years. In this paper micro structure of RAC and mixing approaches conducted by many researchers are critically studied for the enhancement of strength and durability of RAC. The findings and recommendations derived from the earlier research may be helpful for the design engineers and professionals for proper design of structural components using RAC. This will also help in popularizing the use of recycled concrete aggregate in Civil Engineering field. Applications/Improvements: To achieve sustainable issue in construction area the use of waste concrete as RAC is an important focus for construction industries and for the safe guard of the natural environment.

Comparative study of effect of raw and densified silica fume in the paste, mortar and concrete

The differences of effect of silica fume in paste, mortar and concrete were studied by determining the non-evaporable water content of pastes, measuring the compressive strengths of pastes, mortars and concretes containing 5% and 10% raw silica fume or densified silica fume with water-to-binder ratios (W/B) of 0.29 and 0.24 and investigating the properties of interfacial transition zone between hardened paste and aggregate. The results show that silica fume can significantly increase the hydration degree of paste. The addition of silica fume trends to increasing the compressive strengths of hardened pastes, mortars and concretes, and the strength activity index of densified silica fume in concrete is the highest while that in paste is the lowest. The agglomeration of silica fume has been found in blended paste which is hardly seen in concrete. The silica fume can improve the interface bond strength between hardened cement paste and aggregate. The crystalline orientation degree, the crystalline size and the content of calcium hydroxide at the interface are obviously decreased by adding silica fume. The different dispersion and the improvement of the interfacial transition zone are the main factors causing the different role of silica fume in paste, mortar and concrete.

Understanding the mechanical and interfacial properties of core–shell structured bamboo–plastic composites

ABSTRACTCore–shell structured bamboo–plastic composites (BPCs) were directly prepared with a single‐screw/single‐screw coextruder system. The effects of different shell layers, such as high‐density polyethylene (HDPE), bamboo pulp fiber (BPF)/HDPE, and white mud (WM)/HDPE, were studied in the context of the mechanical properties and the characteristics of the interfacial transition zone (ITZ) of BPC. The mechanical properties of the core–shell structured BPC were characterized by flexure, short‐beam shear, and impact tests. The surface morphologies of BPC were analyzed with field emission scanning electron microscopy. The ITZ properties were studied with dynamic mechanical analysis and nano‐indentation testing. The results show that the flexural properties, short‐beam strength, and impact strength decreased profoundly in the presence of BPF or WM. The dynamic mechanical analysis results suggest that the ITZ properties decreased, as indicated by the reductions in the storage modulus, loss modulus, and loss factor; the nano‐indentation results show that on the addition of BPF or WM, a gradient in the hardness and modulus of elasticity appeared across ITZ. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43053.

Micromechanical Modeling of Transport Properties of Cement-Based Composites: Role of Interfacial Transition Zone and Air Voids

The transport properties of cement-based composites, including solute diffusivity, electrical conductivity and water permeability, are regarded as durability indicators of cement-based composites. These transport properties are closely related to the microstructure, or rather to the pore structure of materials. Among all the microstructural aspects, the interfacial transition zone (ITZ) between the cement paste matrix and aggregates, and the air voids are believed to play an essential role in the transport properties. However, their impacts on the transport properties are difficult to be quantified. This paper develops a closed-form four-phase micromechanical model accounting for the local properties of ITZ and the saturation states of air voids. The effects of ITZ and air voids on the transport properties of cement-based composites are addressed quantitatively in the model. The Katz–Thompson equation is reinterpreted by the model in particular. It is shown that the local properties of ITZ and volume fraction of aggregates act mutually on the overall transport properties, the influence of air voids depends significantly on the water saturation, and a critical saturation degree is found to be 1/3.

Statistical relationship between mix properties and the interfacial transition zone around embedded rebar

The relationship between concrete mix properties and the properties of the interfacial transition zone (ITZ) formed around embedded rebar was investigated. Multiple samples of various mix compositions and bar orientations were prepared so as to represent common concrete technology. Water-to-cement ratios varied from 0.40 to 0.65 and powder (cement+limestone filler) contents ranged from 362kg/m3 to 564kg/m3. Over 1300 BSE images of the steel–concrete interface were taken and analyzed automatically. Statistical methods were used to identify correlations between ITZ properties and mix composition or fresh mix properties.A single large void was identified beneath all horizontal bars regardless of concrete composition. The ITZ around vertical bars was more uniform and extended around the entire rebar. No clear relationship was found between ITZ thickness and mix composition or fresh mix properties for either vertical or horizontal bar orientations. The degree of ITZ variability beneath horizontal bars clearly depends, however, on the bleeding properties of the mix. The distance from steel surface to the closest concrete solid, which influences the chemistry over the surface of the steel, is affected by precipitation of hydration products in horizontal bars, but not by mix composition.