Interfacial Zone Percolation in Concrete: Effects of Interfacial Zone Thickness and Aggregate Shape

1994 ◽  
Vol 370 ◽  
Author(s):  
D.P. Bentz ◽  
J.T.G. Hwang ◽  
C. Hagwood ◽  
E.J. Garboczi ◽  
K.A. Snyder ◽  
...  
Keyword(s):  
Transition Zone ◽  
High Performance ◽  
Dynamic Range ◽  
Hard Core ◽  
Concrete Specimen ◽  
Interfacial Transition Zone ◽  
Interfacial Zone ◽  
Transition Zones ◽  
Soft Shell ◽  
Aggregate Shape

AbstractPreviously, a hard core/soft shell computer model was developed to simulate the overlap and percolation of the interfacial transition zones surrounding each aggregate in a mortar or concrete. The aggregate particles were modelled as spheres with a size distribution representative of a real mortar or concrete specimen. Here, the model has been extended to investigate the effects of aggregate shape on interfacial transition zone percolation, by modelling the aggregates as hard ellipsoids, which gives a dynamic range of shapes from plates to spheres, to fibers. For high performance concretes, the interfacial transition zone thickness will generally be reduced, which will also affect their percolation properties. This paper presents results from a study of the effects of interfacial transition zone thickness and aggregate shape on these percolation characteristics.

scholarly journals Effect of water/cement ratio on micro-nanomechanical properties of the interface between cementitious matrix and steel microfibers in ultra-high performance cementitious composites

2021 ◽  
Vol 14 (4) ◽  
Author(s):  
Vanessa Fernandes Cesari ◽  
Fernando Pelisser ◽  
Philippe Jean Paul Gleize ◽  
Milton Domingos Michel
Keyword(s):  
Transition Zone ◽  
Cement Paste ◽  
Calcium Silicate ◽  
High Performance ◽  
Calcium Silicate Hydrate ◽  
Interfacial Transition Zone ◽  
Cement Ratio ◽  
Water Cement Ratio ◽  
Nanomechanical Properties ◽  
Cementitious Matrix

abstract: Ultra-high performance concretes with steel microfibers have been studied in depth with the aim of producing more efficient and durable structures. The performance of these materials depends on the characteristics of the interface between microfibers and cementitious matrix. This research investigates the micro-nanomechanical properties of the interfacial transition zone between the steel microfibers and the matrix of ultra-high performance cementitious composite. The effect of the water/cement ratio and distance from the microfiber were analyzed. The results confirm the formation of high-density calcium-silicate-hydrate (HD C-S-H) matrix at higher concentrations than low-density calcium-silicate-hydrate (LD C-S-H) for w/c ratios of 0.2 and 0.3. The properties in cementitious matrix interface with steel microfibers were very similar to that measured for the cement paste, and no significant difference was observed regarding the distance to the microfibers in relation to the elastic modulus, hardness and chemical composition. Thus, the authors can conclude that the formation of a less resistant region does not occur at the interfacial transition zone cement paste/microfibers.

The Influence on High-Temperature Mechanical Properties of Hybrid-Fiber-Reinforced High-Performance Concrete and Microscopic Analysis

2012 ◽  
Vol 226-228 ◽  
pp. 1709-1713
Author(s):  
Lan Yan ◽  
Y.M. Xing ◽  
Ji Jun Li
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Transition Zone ◽  
High Performance ◽  
Room Temperature ◽  
Steel Fiber ◽  
High Performance Concrete ◽  
Interfacial Transition Zone ◽  
Hybrid Fiber ◽  
High Temperature Mechanical Properties

This paper investigated the high temperature mechanical properties of the hybrid fiber reinforced high performance concrete (HFHPC) and normal concrete (NC) .After being subjected to different elevated heating temperatures, two kinds of concretes have been tested for the compressive strength, splitting tensile strength and flexural strength of test specimen at room temperature and 200 °C,400 °C,600 °C,800 °C.Microstructure changes of concrete were also observed by using Scanning Electron Microscopy (SEM) after high temperature. The results show that the hybrid fiber can significantly increase mechanical properties of the concrete at room temperature and high temperature. SEM and XRD analysis shows that there is a permeable diffusion layer in the steel fiber surface because of solid state reaction in the Interfacial Transition Zone of steel fiber and concrete. This permeable diffusion layer is white, bright, serrated and mainly consist of FeSi2 and the complex hydrated calcium silicate. The compounds of this layer change the Interfacial Transition Zone structure, enhance bonding capacity of the steel fiber and matrix, and increase the high temperature mechanical properties of concrete.

scholarly journals The Application of Berkovich nanoindenter to the study of interfacial transition zone in concretes containing fly-ash

2014 ◽  
Vol 13 (2) ◽  
pp. 085-092
Author(s):  
Grzegorz Golewski
Keyword(s):  
Fly Ash ◽  
Grain Boundary ◽  
Transition Zone ◽  
Interfacial Transition Zone ◽  
Berkovich Indenter ◽  
Fly Ashes ◽  
Transition Zones ◽  
Coarse Aggregates ◽  
Percent Increase ◽  
Technique Analysis

The paper presents the results of nanohardness (HB) in the Interfacial Transition Zones (ITZ) of concretes with the addition of 0, 20 and 30% siliceous fly ashes (FA). A compact platform CSM Instruments was used in the testing. An area in the ITZ of coarse aggregates with paste was analysed in the five measurement points during the experiments, i.e. at the distance of: 5, 25, 50, 100 and 150 µm from the grain boundary. The indents in concrete were create by Berkovich indenter using DSI technique. Analysis of the results revealed that the 20% additive of FA causes a few percent increase in nanohardness, while 30% FA additive leads to between ten and twenty percent drop of HB. On the basis of nanohardness distributions in particular concretes, it was found that the most heterogeneous one is the ITZ zone within the distance of 25µm from the aggregate grain.

Effect of Aggregate Shape on the Chloride Diffusivity of Concrete

2012 ◽  
Vol 450-451 ◽  
pp. 150-153 ◽  
Author(s):  
Xin Zhu Zhou ◽  
Jian Jun Zheng ◽  
Yun Ying Liang
Keyword(s):  
Numerical Method ◽  
Transition Zone ◽  
Interfacial Transition Zone ◽  
Area Fraction ◽  
Lattice Method ◽  
Chloride Diffusivity ◽  
Ellipse Model ◽  
Three Phase ◽  
Quantitative Manner ◽  
Aggregate Shape

The effect of aggregate shape on the chloride diffusivity of concrete is studied. To represent the heterogeneity of concrete, a three-phase composite ellipse model is constructed and the relative dimensions are determined by calculating the area fraction of interfacial transition zone in a numerical manner. The height of each bar in the lattice mesh is derived analytically. The lattice method is then used to estimate the chloride diffusivity of concrete. After the validity of the numerical method is verified with experimental results, the effect of aggregate shape on the chloride diffusivity of concrete is evaluated in a quantitative manner.

scholarly journals Geometrical Modeling of Concrete Microstructure for the Assessment of ITZ Percolation

10.14311/1674 ◽  
2012 ◽  
Vol 52 (6) ◽  
Author(s):  
Daniel Rypl ◽  
Tomáš Bým
Keyword(s):  
Transport Properties ◽  
Hard Core ◽  
Critical Factor ◽  
Interfacial Transition Zone ◽  
Constant Thickness ◽  
Geometrical Modeling ◽  
Multiphase Materials ◽  
And Topology ◽  
Soft Shell ◽  
Aggregate Particles

Percolation is considered to be a critical factor affecting the transport properties of multiphase materials. In the case of concrete, the transport properties are strongly dependent on the interfacial transition zone (ITZ), which is a thin layer of cement paste next to aggregate particles. It is not computationally simple to assess ITZ percolation in concrete, as the geometry and topology of this phase is complex. While there are many advanced models that analyze the behavior of concrete, they are mostly based on the use of spherical or ellipsoidal shapes for the geometry of the aggregate inclusions. These simplified shapes may become unsatisfactory in many simulations, including the assessment of ITZ percolation. This paper deals with geometrical modeling of the concrete microstructure using realistic shapes of aggregate particles, the geometry of which is represented in terms of spherical harmonic expansion. The percolation is assessed using the hard core – soft shell model, in which each randomly-placed aggregate particle is surrounded by a shell of constant thickness representing ITZ.

Digital-Image-Based Computer Modeling and Visualization of Cement-Based Materials

1996 ◽  
Vol 1526 (1) ◽  
pp. 129-134
Author(s):  
Dale P. Bentz ◽  
Edward J. Garboczi
Keyword(s):  
Computer Modeling ◽  
Cement Paste ◽  
Digital Image ◽  
Hard Core ◽  
Percolation Model ◽  
Interfacial Transition Zone ◽  
The Past ◽  
Cement Based Materials ◽  
Soft Shell ◽  
Modeling Techniques

Over the past several years, digital-image-based computer models and subsequent visualization of microstructure have proven valuable in studying processing-microstructure-property relationships in cement-based materials. This paper reviews the computer modeling techniques used to simulate the microstructure of hydrating cement paste at the micrometer level and the microstructure of concrete and mortar at the millimeter level. In the former case, digital-image-based models using cellular automata offer many advantages in simulating the reactions occurring during the hydration of cement paste. In the latter case, a continuum hard core-soft shell percolation model appears to be most efficient for modeling the aggregates in a mortar or concrete, each surrounded by an interfacial transition zone (ITZ). Here, digitization is employed to compute the volume fractions occupied by aggregate, bulk cement paste, and ITZ cement paste. The influence of microstructure on the diffusivity of these materials is addressed within the overall framework of this multiscale modeling approach.

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