Role of Thresholding to Determine Size of Interfacial Transition Zone

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Title: Role of Thresholding to Determine Size of Interfacial Transition Zone

Author(s): P. A. M. Basheer, L. Basheer, D. A. Lange, and A. E. Long

Publication: Special Publication

Volume: 189

Issue:

Appears on pages(s): 165-186

Keywords: aggregates; cement matrix; image analysis; microstructure

Date: 1/1/2000

Abstract:
Concrete may be considered a three phase material, consisting of cement matrix, aggregate and the interfacial transition zone (ITZ). The ITZ is studied usually by collecting backscattered electron (BSE) images of polished samples of concrete and by carrying out a quantitative analysis of these images. This technique makes use of the contrast between pores and cement hydrates to analyse the microstructure. Once the images are collected, grey level thresholding is used to segment regions associated with capillary porosity. The size of the ITZ is determined using this data. Different techniques have been suggested to minimise errors introduced at this stage of the analysis. The authors have carried out an investigation on 17 different concrete mixtures in an attempt to assess the role of threshold values. The results indicated that the size of the transition zone is not affected by the range of threshold values used. However, the porosity of both the ITZ and the bulk cement paste varied with different threshold values. The paper proposes a method which can be used to determine a reliable threshold value.