Liliane Chermant

Some fields of applications of automatic image analysis in civil engineering

Abstract This paper illustrates the use of automatic image analysis technique to investigate the morphology of cement, concrete and fibre-reinforced concrete. First the methods to be used for powders and secondly for mortar and concrete are introduced. The dispersed phases are characterized by classical morphological parameters: these also enable to accede to the hydration process. The covariances give quantitative information on the homogeneity and dispersion of the different components: gravel, air-voids and cement paste. Air-voids are characterized by granulometric distributions and their mean free paths. Rose of directions gives information on feature orientation: fibres, microcracks for fibre-reinforced concrete, etc. Finally probabilistic models can be used to simulate the microstructure of such materials.

Automatic image analysis and morphology of fibre reinforced concrete

Abstract Automatic image analysis is an efficient tool to quantify the morphology of materials. Moreover, it can aid to understand their mechanical behaviour. Several applications of automatic methods are presented to investigate concrete reinforced by ribbon shaped amorphous cast iron fibres. Introducing ribbons into the plain matrix entrapped air voids. This affected the workability and, later on, the compressive strength of the fibre reinforced concrete (FRC). Both were improved by additions of superplasticizer in order to keep the water to cement ratio constant. The influence of the superplasticizer and fibre contents on the compactness of the FRC was characterized by the dimensional and the spatial distributions of the air voids. The orientations of fibres and microcracks were quantified by Fourier image transforms. Due to the casting procedure of the FRC, the fibres were located in “horizontal layers”, perpendicular to the casting axis. Whatever the direction of compression with respect to the layers of fibres, the microcrack network was getting more and more oriented in the direction of compression as stresses increased. The analysis of fibre and microcrack orientations suggests that, under uniaxial compression, the inelastic strain domain should be characterized by an anisotropic biaxial damage model, whose principal axes are the orthogonal and parallel directions to the layers of fibres.

STUDY OF PHASE DISPERSION IN CONCRETE BY IMAGE ANALYSIS

Abstract The scope of this paper is to investigate by an automatic image analysis technique the dispersion of phases in concrete. Three morphological and statistical tools were used: co-occurrence matrices, and simple and crossed-covariance. It was shown (1) that there is a repulsion between gravel, (2) that gravel and air-voids are surrounded by matrix (cement paste and sand), and (3) that the dispersion of gravel and air-voids is perfectly uniform.

Distances between air-voids in concrete by automatic methods

Abstract In order to access to the air-void distances in concrete by automatic image analysis, three different methods were proposed, used and discussed: half-distances between two voids nearest neighbours, called count-dilation; half-distances between all neighbours, called SKIZ; and distance function. They were utilized in a euclidean and geodesic way. Some of them can replace favourably the manual methods proposed in the different standards.

Effect of powder processing on microstructure of zirconia during sintering

Abstract The effect of the processing route on both the sintering and mechanical properties of a stabilized zirconia was investigated. Zirconia samples prepared by dry pressing and by tape casting are compared from the point of view of microstructural evolution during thermal treatment and from the point of view of mechanical properties. Kinetics of densification and grain growth are studied by automatic image analysis. The greater homogeneity of the green state obtained by tape casting, in comparison with that obtained by pressing, leads to increased densification and grain growth rates, and to improved mechanical properties.

Morphological characterization of hot-pressed α-SiC with Al-based additives deformed by compression at high temperature

Abstract An automatic image analysis method has been used to study the microstructure evolution of polycrystalline α-SiC samples hot pressed with 0.3 wt% and 1.5 wt% Al-based additives after compression at high temperature. Microstructures have been characterized in terms of grain shape, grain size and grain orientation with respect to the macroscopic stress direction. It has been shown that grains tend to flatten perpendicularly to the external stress for the 0.3 wt% Al grade. By contrast, for the same macroscopic deformation value, grains of the 1.5 wt% Al grade do not exhibit any shape change after creep tests, suggesting that a certain amount of superplastic deformation has occurred.

Texture analysis of ceramic films by image processing

This paper presents an application of automatic image analysis to the morphometry of ceramic sheets. The sheets can be characterized by granulometrie and stereological texture parameters of the granular and the porous phases. Grey level granulometry, automatic thresholding and filtering have thus been used. The results show that the morphology of green sheets is strongly dependent on the ball‐milling conditions.