Mechanical Properties Of Interfacial Transition Zone Research Articles

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.

Erosion damage and expansion evolution of interfacial transition zone in concrete under dry-wet cycles and sulfate erosion

Interfacial transition zone (ITZ) is of paramount importance to the durability of concrete. However, the evolution of damage characteristics and mechanical properties of ITZ under dry-wet cycles and sulfate erosion were not fully investigated in the literature. Therefore, this paper presents the expansive model of ITZ based on cylindrical cavity expansion theory, following by calculation of mechanical properties evolution of ITZ under sulfate erosion. The expansion ratio, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were utilized to analyze the internal erosion and expansion characteristics of concrete with the water-cement ratio (w/c) of 0.3, 0.4 and 0.5. The results indicate that the expansion ratio of concrete increases with the erosion age and w/c. The new diffraction peaks appear in the XRD pattern after sulfate erosion. As compared with Poisson's ratio (γ) and internal friction angle (φ), cohesive force (C) has the largest influence on the internal stress and plastic zone width. The final internal stress and plastic zone width are affected by w/c, and the damage degree of concrete with 0.4 w/c is the minimum. This study provides new insights into damage mechanism of concrete and ITZ under dry-wet cycles and sulfate erosion, the results of which provide new perspectives for improving the durability of concrete.

Experimental study of the chemo-mechanical properties of the interfacial transition zone of concrete

This article presents an experimental study of the chemical and mechanical properties of the cement paste / aggregate interphase. Interfacial Transition Zone (ITZ) represent the contact zone of the cement paste with the aggregate with a thickness of about 20 - 50 μm. This zone has different mechanical and chemical properties compared to the bulk paste. Cement paste / limestone aggregate composite samples were performed to allow the study of the chemical and mechanical properties of ITZ. The cement paste is made with Portland cement with a water/cement mass ratio of 0.4. Calcium concentration profiles in the ITZ show a high concentration of calcium due to the presence of portlandite and ettringite. The nano-indentation tests indicate weakness of ITZ compared to bulk cement paste.

Experimental Study on Interface Strength Between Hardened Cement Paste-Aggregate

The interfacial transition zone (ITZ) is a weak part of concrete, which is the main reason that the mechanical properties of concrete are far lower than those of hardened cement paste and aggregate itself. In order to improve the mechanical properties of concrete ITZ, the effects of cement varieties, water-binder ratio, mineral admixtures and aggregate types on the strength of hardened cement paste-aggregate ITZ were studied by orthogonal test. A linear regression model between interfacial bonding splitting tensile strength and splitting tensile strength of hardened cement paste was proposed. The results show that the water-binder ratio has the greatest impact on the mechanical properties of ITZ, followed by aggregate. The interfacial bonding splitting tensile strength of five kinds of aggregate and cement paste is in the order of marble > coral > granite > basalt > quartzite. The optimal interface test combination is as follows: water-binder ratio 0.25, aggregate is marble, P•O52.5 cement, slag content 15%, fly ash content 20% and silica fume content 10%. The optimal cement slurry combination is: water-cement ratio 0.25, basic magnesium sulfate cement, slag content 15%, fly ash content 20% and silica fume content 10%. The linear regression model between interfacial bond splitting tensile strength and hardened cement paste splitting tensile strength is established by dividing aggregate, which is of great significance to study the law of interfacial strength.

Quantitative characterization of anisotropic properties of the interfacial transition zone (ITZ) between microfiber and cement paste

A new approach to characterize ITZ between microfiber and cement matrix is reported. Results show that microstructure of hydrated cement paste is highly modified in the vicinity of microfibers, with higher porosity and less anhydrous cement. ITZ can extend up to 100 μm from the interface into the matrix. The larger extent of ITZ suggests that perturbation due to inclusion of microfibers to packing of cement grains is severer than that due to inclusion of aggregates. Furthermore, ITZ between microfiber and cement matrix is highly heterogeneous along its axial direction. Existing ITZ analysis methods performed on 2-D cross-sectional plane intersecting with fiber axis thus can lead to errors and uncertainties. Mechanical properties of ITZ between microfiber and cement matrix are anisotropic. Stiffness and ductility of ITZ in the radial direction are 31% and 28% higher than that in the tangential direction, respectively.

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.