Characteristics Of Interfacial Transition Zone Research Articles

Investigation of gradient properties for cement mortar interfacial transition zones and their effects on mechanical characteristics using micro-CT

The interfacial transition zone (ITZ) in cement-based composites with aggregates is widely recognized as the most vulnerable component, greatly affecting their physical and mechanical properties. In this study, the effect of the ITZ characteristics on the mechanical behavior of cement mortar using its actual microstructure was investigated with image-based numerical approaches in this study. The volumetric information of the ITZ of the mortar sample was obtained and characterized from high-resolution synchrotron micro-computed tomography (micro-CT) images. The mechanical properties of the mortar were evaluated using the finite element method, based on the components characteristics represented by grayscale information of the micro-CT images. It was found that the adhesion between the aggregates and binder was well replicated in the simulation with the multiple-phase model, based on the gradient characteristics and properties of the ITZ. Considering the ITZ thickness according to the aggregates size, a more realistic crack propagation trend can be observed. The obtained results confirmed the significant influence of the ITZ thickness and phase distribution characteristics on the mechanical properties of cement mortars, emphasizing the importance of considering ITZ phases for accurate material analysis.

Microstructural characteristics of bonding interfacial transition zone of concrete and magnesium ammonium phosphate cement

Microstructural characteristics of bonding interfacial transition zone (ITZ) are vital to the bonding performance of new-old concrete, which remains difficult to characterize accurately. In this paper, the microstructural characteristics of ITZ based on magnesium ammonium phosphate cement (MPC) bonding to ordinary Portland concrete (OPC) were investigated by the combination of BSE-EDS and microhardness. It was found that ITZs were distinguished into MPC bonding to OPC paste (ITZ-P) and aggregate (ITZ-A). Meanwhile, Gaussian Kernel Smoothing was suitable to the statistical analysis of microhardness. The peak interval of microhardness in ITZ-P for 113.1 MPa was higher than that in ITZ-A for 87 MPa. It was reflected by the observation of denser hydration products and calculation of lower porosity in ITZ-P, especially the observation of enriched pore area in ITZ-A. Moreover, based on the interrelation of indentation lattice and corresponding distribution of element, the hydration products was quantitatively analyzed. The denser hydration products and lower porosity in ITZ-P are 41.4% and 4.3%, respectively, compared with the 29.3% and 12.5% in ITZ-A. The exposure of more aggregate is not conducive to the attachment of the hydration products of MPC.

Investigation of the Wet and Thermal Conditions Effect on the Micro-Scale Characteristics of Interfacial Transition Zone of Porous Asphalt Mixture

Complex environmental factors can significantly influence the micro-properties of porous asphalt (PA) mixture. Therefore, the effects of short-term and long-term thermal aging and moisture immersion on the micromechanics properties, micro-morphology, and chemical element distributions of the interfacial transition zone (ITZ) of PA mixture were studied to reveal the mechanisms by which environmental degradation impact performance by means of nanoindentation (NI), backscattering scanning electron microscope (BSEM), and energy-dispersive X-ray spectroscopy (EDS) analysis techniques. The results show that the ITZ is not the softest part of the PA mixture, and the order of modulus is aggregate > ITZ > asphalt mastic. ITZ thickness is about 10–20 μm. Thermal aging has negligible effect on the width of ITZ. With increasing aging degree, the asphalt mastic and ITZ modulus increase, while water damage reduces the modulus of ITZ and slightly increases the width of ITZ. Thermal aging has little effect on the morphology of ITZ, while water damage will lead to microcracks and micropores in ITZ. Compared with thermal aging, water damage has a greater effect on the morphology of ITZ and leads to softening of the interfacial transition zone and asphalt mastic phase. The width of ITZ obtained by EDS line scanning is basically consistent with that of nanoindentation. Overall, external environmental factors have a more significant effect on the mechanical properties than the micro-morphology of ITZ. The outcomes of this research provide a better understanding of the impact of the service environment on the microscopic characteristics of PA mixture.

Microstructural Characterization of ITZ in Copper Slag Concrete Composite

The use of copper slag as an alternative to natural fine aggregates in concrete construction has two advantages: effective management of hazardous waste and assistance in conserving natural resources. In order to build confidence among stakeholders and to improve the utilization of copper slag in concrete construction to the required extent, this article evaluates the interfacial transition zone (ITZ) of hardened copper slag concrete composites through various experimental studies. This includes tests on compressive and split-tensile strengths, sorptivity, microhardness, and microcrack properties of ITZ. This paper also examines the surface morphology of ITZ along with its elementary compositions using field emission scanning electron microscopy (FESEM) imaging and energy dispersion spectroscopy (EDS) analysis. The results show that copper slag improves the ITZ characteristics of hardened concrete due to its higher level of pozzolanic reactivity compared to natural sand.

Particle size distribution of aggregate effects on the reinforcing roles of carbon nanotubes in enhancing concrete ITZ

By virtue of their superior mechanical properties and huge surface area, carbon nanotubes (CNTs) have become a potential representative in the field of the nanoengineered concrete, which provides an excellent opportunity to reinforce concrete interfacial transition zone (ITZ) characteristics. Adjusting the most reasonable aggregate gradation of concrete to maximize the enhancement effects of CNTs to ITZ is the key to popularizing the application of nano reinforcement in practical engineering. Hence, in this work, we investigated the reinforcing roles and mechanisms of CNTs on the concrete ITZ, and the corresponding influence on the mechanical performance and impermeability properties under different aggregate particle size distributions. The results reveal that CNTs can promote nucleation effects to generate hydration products growth and act as the refined templates to produce finer microstructure in concrete ITZ. Compared with plain concrete, the reinforcing ratios of CNTs on the ITZ characteristics, mechanical performance and impermeability present a quadratic function correlation with the Talbot index. The optimal effects of CNTs on the reinforcement of concrete ITZ characteristics appear at 0.8 Talbot index, reducing about 30% ITZ width and 22.8% abrasion crack width in ITZ. The corresponding mechanical properties and impermeability improve 20.7–35.6% and 38.1–43.6%, respectively. Low Talbot gradation index would result in the uneven dispersion of CNTs among the capillary pores. In contrast, high Talbot gradation index may enlarge the ITZ range, increase the amount and width of abrasion cracks in ITZ, and further weaken the reinforcing effects of CNTs.

Effect of Interfacial Transition Zone on diffuse ultrasound in thermally damaged concrete

The correlation between Interfacial Transition Zone (ITZ) and the diffusion of ultrasound for the Non Destructive Evaluation of thermally damaged concrete is investigated in this study. As most damages first emerge from the ITZ, it is necessary to understand the ultrasonic wave/ITZ interaction. This paper focuses on the use of the diffusivity parameter to characterize thermal damage within the microstructure. A numerical model accounting for real ITZ characteristics and validated through a previous study is used to assess the effects of ITZ on diffusivity values. Diffusivity measurements are performed on real concrete specimens with different thermal damage states. Comparison of experimental and numerical data exhibits a strong correlation between the ultrasonic diffusivity, the thermal damage level and the ITZ contact level. A direct correlation between diffusivity and ITZ characteristics is suggested. This result is a major step toward the development of quantitative ultrasonic methods for the NDE of concrete.

Numerical Analysis of Effective Permeability of Concrete-Like Material With a Random Three-Phase Mesostructure

Interfacial transition zone (ITZ) is an important component of a concrete-like material. Accurately simulating the ITZ's characteristics of the concrete-like materials is a difficult process in numerical simulation. This article proposed a random three-phase mesostructural modeling method using the incorporation of random aggregate generation, Minkowski sum theory, and polygon union techniques. It was found that this method can better simulate the mesostructure and ITZ characteristics of concrete-like materials. By using this method, a random three-phase mesostructural model had been built for conducting a finite element analysis to investigate the effective permeability parameters of concrete. A good agreement between numerical and experimental results indicates the feasibility of this method in the concrete-like material analysis.

Mechanical properties, durability, and ITZ characteristics of full-grade dam concrete prepared by aggregates with surface rust stains

Aggregates with surface rust stains (ASRS) is very common in the construction of water conservancy and hydropower projects. The purpose of this paper is to provide the possibility to utilize rusted raw rocks as aggregate in dam concrete. The physical and chemical properties of rusted raw rocks are measured. In addition, comparisons of their mechanics and the durability of dam concrete prepared by ASRS and rust-free limestone aggregates (RFLA) are investigated. The characteristics of interfacial transition zone (ITZ) between aggregate and paste are investigated by the means of scanning electron microscope with energy dispersive spectrum (SEM-EDS) and nano-indentation technology. The results show the apparent density and uniaxial compressive strength of ASRS are lower than the RFLA by 10 kg/m3 and 5.3 MPa, respectively. The compressive strengths of ASRS concrete are approximate those of RFLA concrete. The tensile strength of ASRS concrete is lower than that of RFLA concrete by 13 %. The ASRS slightly reduces the dam concrete frost resistance and impermeability. The ITZ average thickness of the ASRS sample is thicker than that of the RFLA sample by 15.0–20.0 μm. The values of indentation modulus and hardness observed across the ITZ in the ASRS sample are lower than those of the RFLA sample by 6.31 GPa and 0.11 GPa, respectively. The ASRS can be utilized as aggregates in dam concrete, such as in the structure with lower tensile strength requirements.

Influence of ultrasonication energy on reinforcing-roles of CNTs to strengthen ITZ and corresponding anti-permeability properties of concrete

Concrete is the most common material used extensively in fundamental construction and engineering. The interfacial transition zone (ITZ), as the region of the cementitious pastes around the aggregate particles, is the weakest area and always limits the performance and application of the concrete. In this study, we used carbon nanotubes (CNTs) as nano-additives to strengthen the ITZ characteristics in concrete and the corresponding anti-permeability reinforcement under different ultrasonication energy (UE). The results prove that balancing the separating and shearing forces during the ultrasonication processes is crucial to ensure the dispersion and suitable particle size of CNTs in their further application. It is found that ultrasonication energy of between 225 J/mL and 338 J/mL can simultaneously ensure the degree of dispersion and the tube-length of CNTs in the suspension, and optimize the ITZ width and abrasion crack width in the ITZ in concrete to 30%–40.2%. The relationship between the ITZ characteristics and UE can be described using a quadratic function. Both the ITZ width and abrasion crack width in the ITZ have a linear correlation with permeability-related parameters in the concrete. After mixing CNTs into concrete specimens, the corresponding anti-permeability properties increased by more than 43% under 270–338 J/mL UE. Scanning electron microscopy observation further reveals that CNTs not only have a nucleating role in generating a higher hydration reaction but also form net-like distributions in the hardened concrete to reinforce the microstructure of the ITZ. However, both insufficient and excess UE will inhibit the superior reinforcing ability of CNTs.

Nanomechanical Characteristics of Interfacial Transition Zone in Nano-Engineered Concrete

This study investigates the effects of nanofillers on the interfacial transition zone (ITZ) between aggregate and cement paste by using nanoindentation and statistical nanoindentation techniques. Moreover, the underlying mechanisms are revealed through micromechanical modeling. The nanoindentation results indicate that incorporating nanofillers increases the degree of hydration in the ITZ, reduces the content of micropores and low-density calcium silicate hydrate (LD C–S–H), and increases the content of high-density C–S–H (HD C–S–H) and ultrahigh-density C–S–H (UHD C–S–H). In particular, a new phase, namely nano-core-induced low-density C–S–H (NCILD C–S–H), with a superior hardness of 2.50 GPa and an indentation modulus similar to those of HD C–S–H or UHD C–S–H was identified in this study. The modeling results revealed that the presence of nanofillers increased the packing density of LD C–S–H and significantly enhanced the interaction (adhesion and friction) among the basic building blocks of C–S–H gels owing to the formation of nano-core–shell elements, thereby facilitating the formation of NCILD C–S–H and further improving the performance of the ITZ. This study provides insight into the effects of nanofillers on the ITZ in concrete at the nanoscale.

Environmental impact, durability performance, and interfacial transition zone of iron ore tailings utilized as dam concrete aggregates

This paper discusses the utilization of iron ore tailing aggregates (IOTA) as a replacement for normal aggregates (NA) in dam concrete for hydraulic engineering applications. The durability performance of concrete prepared using IOTA and NA, including resistance to chloride-ion permeability, sulfate corrosion resistance, and abrasion-erosion resistance, are investigated in this study. Based on it, the interfacial transition zone (ITZ) characteristics of IOTA and NA samples are examined by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and microscopic nanoindentation. Besides, the economic and environmental evaluations of the IOTA utilization in real hydraulic engineering are proposed. The results show the concrete prepared with IOTA has more superior durability than NA. The abrasion resistance of concrete prepared with IOTA is higher than that of the NA sample by 1.32–2.90 h m2/kg. Since the IOTA raw rock has higher compressive strength, lower saturated-surface-dry (SSD) water absorption, and angular shape, the concrete prepared with IOTA has more superior ITZ characteristics and durability performance than NA. Significant economic and environmental benefits of the utilization of IOTA in hydraulic engineering are obtained. The investments into the IOTA utilization in two practical hydraulic engineering applications can save 8.98 × 106 USD. It can also reduce the occupied land space, CO2 emission, and water consumption by 151 900 m2, 8157.0 t, and 942 000 m3. The relative reductions of CO2 emission and water consumption, as compared to NA, are 15.7 and 27.4%.

Roles of carbon nanotubes in reinforcing the interfacial transition zone and impermeability of concrete under different water-to-cement ratios

Concrete plays a central role in fundamental construction and engineering. However, the interfacial transition zone (ITZ), as the area between the aggregates and cementitious pastes, is the weakest component in concrete and always limits the properties and application of the concrete. Here, we reveal the potential of carbon nanotubes (CNTs) as superior additives for reinforcing the ITZ in concrete and the corresponding impermeability enhancement against various of water-to-cement (W/C) ratios. The results suggest that CNTs not only promote higher hydration reaction and generate more hydrated products to dense ITZ area, but also form net-like distributions to inhibit flaws propagation at the microscale. Compared with the plain concrete specimens, the addition CNTs micrified the ITZ width by 14.3–30% and reduced the abrasion crack width by 19.5–35%. The reinforcing effects of CNTs on ITZ characteristics are consistent with Gauss fitting and achieve the highest enhancement at 0.4 W/C ratio. The corresponding impermeability properties of concrete present a linear correlation with both ITZ width and abrasion crack width, which can be strengthened by approximately 10.9%-35.8% assisted by CNTs. Furthermore, selecting the appropriate W/C ratios is the key to make full use of CNTs roles in strengthening the ITZ of concrete. High W/C ratios may lead to the re-agglomeration of CNTs and low W/C ratios would promote CNTs to act as pulled-out roles and weaken their ability to inhibit flaws propagation.

Improvement in freeze-thaw durability of recycled aggregate permeable concrete with silane modification

Currently, there are few effective methods for improving the freeze–thaw durability of recycled aggregate (RA) permeable concrete without reducing the strength or permeability. Thus, this study aims to improve the freeze–thaw durability of recycled aggregate permeable concrete without the degradation of strength and permeability. Accordingly, two silane emulsion modification methods, namely the surface modification of recycled aggregate and integral modification of cement matrix, were used to raise the freeze–thaw durability. The compressive strength, permeability coefficient, freeze–thaw durability of recycled aggregate permeable concrete were measured. The characteristics of interfacial transition zone (ITZ) and cement matrix were investigated to analyse the modification mechanism. The results indicate that surface modification of recycled aggregate can increase both the compressive strength and freeze–thaw durability of recycled aggregate permeable concrete more effectively than the integral modification of cement matrix. This study provides an effective method to improve the comprehensive performance of recycled aggregate permeable concrete.

Damage mechanism and interfacial transition zone characteristics of concrete under sulfate erosion and Dry-Wet cycles

The durability of concrete structures under sulfate attack is of paramount importance to the structural safety and serviceability. Previous relevant researches have considered concrete as a single phase and homogeneous material in experiments without analyzing its multi-phase and heterogeneous properties. In addition, the damage mechanism of concrete under sulfate attack at the microscopic level, i.e., interfacial transition zone (ITZ), was not fully explored in literature. Therefore, this paper provided a comprehensive investigation on the damage mechanism and ITZ characteristics of concrete under sulfate attack and dry-wet cycles. Two typical sulfate attack conditions were examined in an experimental study, which includes 10% Na2SO4 and 10% MgSO4 solutions (by mass), respectively. The deterioration process of concrete was investigated by inspecting the visual change, corrosion resistance coefficient, and ions transportation. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Atomic Force Microscopy (AFM) were also utilized to analyze the micro-topography change and corrosion products of concrete. The results indicate that the porosity of ITZ increases with the dry-wet cycles in tap water, and the concrete microstructure can be compensated by sulfate solutions, in which cases the compensation of C30 concrete is more remarkable than that of C60. 10% Na2SO4 solution is found to exhibit a stronger compensation effect than 10% MgSO4 solution. However, such compensation effect cannot offset the sulfate erosion damage on the microstructure of concrete. As a result, the porosity and initial cracks of ITZ continue to expand, and finally accelerate the cracking process and deterioration of concrete. It is also found that that under the combined effect of sulfate corrosion and dry-wet cycles, the roughness of ITZ increases with exposure time together with the largest increase in tap water. This study provides new insights and deeper understanding into the deterioration process and ITZ-link characteristics of concrete under sulfate erosion, the results of which serve as a decision basis for more durable concrete structure design.

Microhardness characteristics of high-strength cement paste and interfacial transition zone at different curing regimes

In order to understand the influencing mechanisms of curing temperature on the performances of steam cured concrete further, the microhardness characteristics of the interfacial transition zone between cement paste and coarse aggregate under different curing temperatures were studied through microhardness measurements, backscattered electronic microscopy (BSEM) and mathematical statistical analysis. The experimental results indicate that the microhardness of the hardened cement paste presents a significant statistical distribution characteristic. That is to say, there are two microhardness characteristic values which reflect the hydrated products and unhydrated cement particles, respectively. The curing temperature has a significant effect on the microhardness of interfacial transition zone. In other words, the microhardness decreases, and the thickness range of interfacial transition zone increases with increasing the curing temperature. The relationship of the microhardness value of the interfacial transition zone to the distance from the aggregate surface conforms to the Peal function.

Effect of type of coarse aggregate on the strength properties and fracture energy of normal and high strength concrete

An attempt has been made in the present work to study the effect of type of coarse aggregate on the strength properties and fracture energy of M30, M50 and M80 grade of concretes. The aggregate used in this study includes Grey Granite (GG), Anorthosite (AS) Charnockite (CK) Limestone, (LS) and Gneiss (GS). The result shows that the strength of concrete is greatly influenced by the aggregate types in high strength concrete. However, the aggregate has not impacted the Normal Strength Concrete as the strength is governed by the characteristics of interfacial transition zone, rather than aggregate. Among all aggregates, the Grey Granite aggregate has produced concrete with highest compressive strength followed by Anorthosite, Charnockite, Limestone and Gneiss indicating that the surface texture, structure and mineralogical composition played a dominant role. The similar trend was noticed even in fracture energy and modulus of elasticity of high strength concrete.

Micro-structural behavior of interfacial transition zone of the porous sintered fly ash aggregate

The interfacial transition zone (ITZ) has a significant influence on the hardened concrete behavior. The behavior of ITZ is not well established in the case of sintered fly ash aggregate (SFA) concrete compared to normal aggregate concrete. The present study emphasizes to quantify the characteristics of ITZ of the SFA concrete. To understand the influence of water-cement ratio on the ITZ behavior, various water-cement ratios ranging from 0.25 to 0.75 were employed and the ITZ characteristics were assessed both at 28 and 90 days through various experimental methods such as microhardness test, SEM-EDX and impedance spectroscopy. Also, a comparison is made with the ITZ of the normal granite aggregate concrete. The results indicate that the ITZ formed in the SFA aggregate concrete is denser than the normal aggregate concrete.

Multi-scale modelling for diffusivity based on practical estimation of interfacial properties in cementitious materials

The interfacial transition zone (ITZ) between matrix and aggregate is a weak region because of its physical nature of relatively high porosity and low rigidity. ITZ microstructural configurations such as its thickness and volume fraction play an important role in transport and mechanical behaviours of cementitious composites. However, such ITZ characteristics are usually overestimated since random sampling planes from conventional sectional plane analysis technologies rarely pass through the normal to the surface of anisotropic aggregates. In this study, we first propose a normal line sampling (NLS) algorithm to evaluate the overestimation degrees of these microstructures for complex geometrical shaped aggregates like Platonic particles. The NLS algorithm applies the sampling lines along the normal of aggregate boundary at the given section plane that is significantly different from the previous methods in the literature. Then, the ITZ volume fraction can be determined by the ITZ thickness according to a generalized formula. We also extend these practical ITZ characteristics to estimate the effective diffusivity of cementitious composites by the classical effective medium approximation. The derived results show that the ratio of the apparent ITZ thickness to the actual ITZ thickness is dependent on the sphericity which is a shape descriptor of particles. Moreover, the overestimation degree of ITZ volume fraction and diffusivity of three-phase composites are governed by aggregate volume fraction, particle size distribution and particle shape. Finally, the results reflect that the aggregate shape has a significant effect on the apparent ITZ thickness, and the sampling process of ITZ thickness by using NLS algorithm is similar to the sampling techniques in experiment.

Effects of Mineral Admixtures on Microstructure-linked Strength Properties of Macro-synthetic Fiber Reinforced Concrete

This study investigates the effects of fly ash and silica fume on the mechanical properties and microstructure characteristics of interfacial transition zone (ITZ) between macro-synthetic fiber and the bulk matrix of the fiber reinforced concrete. The experimental results show that the concrete is able to withstand significant post-cracking loads and undergo remarkable deflections under flexural loads due to the bridging effect of macro-synthetic fiber. The mechanical properties of concrete incorporating fly ash plus silica fume are much better than those prepared with no mineral admixtures or mono addition. The work of adhesion is an integrated index to evaluate the bonding behaviors between fiber and matrix, which exhibits a trend similar to that noted in the flexural toughness. The compound addition of fly ash and silica fume presents the most distinct improvement effects on microstructure of ITZ and the bonding behaviors between fiber and matrix. The amount of hydrated calcium silicate (C-S-H) gel and compaction of ITZ play key roles in the fiber - matrix interfacial bond and the mechanical properties of concrete.

Influence of incorporation of nano-silica and recycled aggregates on compressive strength and microstructure of concrete

The present investigation deals with the study of compressive strength and characteristics of the Interfacial Transition Zone (ITZ) of concrete containing recycled aggregates and nano-silica. For this purpose, compressive strength at 7, 28, 90 and 365days are determined for fully natural and recycled aggregate concrete mixes made with or without nano-silica. In addition to above, Vickers microhardness test and backscattered-mode scanning electron microscopic analysis is carried to characterize ITZ of concrete mixes. The results of study depict that full replacement of natural coarse aggregates with recycled ones have significant effect on compressive strength and ITZ characteristics of concrete. However, compressive strength and microstructure of concrete mixes improves with the incorporation of nano-silica.