ThreePhase Composite Sphere Model for the Prediction of Chloride Diffusivity of Concrete
In predicting the chloride diffusivity of concrete as a threephase material, the morphological characteristics of the three phases, the physical properties of each phase constituent material, and the interactions of the three phases in the concrete matrix should all be taken into account. The present paper attempts to develop an analytical method to achieve this. A threephase composite sphere model for the concrete matrix is proposed to represent the heterogeneous nature of concrete and a closed form solution for the chloride diffusivity of concrete is derived. After verifying the derived closed form solution with experimental results, the effects of key factors that affect the chloride diffusivity of concrete, namely the chloride diffusivity and thickness of the interfacial transition zone (ITZ), the maximum aggregate diameter, and the aggregate gradation are examined in a quantitative manner. It is found in the paper that the most important factor influencing the chloride diffusivity of concrete is the chloride diffusivity of ITZ. When the aggregate volume fraction is equal to 0.8, the relative chloride diffusivity of concrete to cement paste for a given relative chloride diffusivity of ITZ to cement paste at 10 is almost four times that for a given relative chloride diffusivity of ITZ to cement paste at 2. The second most important factor is the thickness of ITZ. When the aggregate volume fraction is equal to 0.8, the relative chloride diffusivity of concrete to cement paste for a given ITZ thickness at 0.05 mm increases by 76% as compared to that for a given ITZ thickness at 0.02 mm. The least important factors are the maximum aggregate diameter and aggregate gradation. The extent to which they influence the chloride diffusivity of concrete is in the range of 10–55%. The paper concludes that the closed form solution derived here can predict the chloride diffusivity of concrete with reasonable accuracy.

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Authors:
 Zheng, Jianjun
 Zhou, Xinzhu
 Publication Date: 20083
Language
 English
Media Info
 Media Type: Print
 Features: Figures; Illustrations; References;
 Pagination: pp 205211

Serial:
 Journal of Materials in Civil Engineering
 Volume: 20
 Issue Number: 3
 Publisher: American Society of Civil Engineers
 ISSN: 08991561
 EISSN: 19435533
 Serial URL: http://ascelibrary.org/journal/jmcee7
Subject/Index Terms
 TRT Terms: Aggregate gradation; Cement paste; Chlorides; Concrete; Diffusivity; Mathematical models; Mathematical prediction; Physical properties; Thickness; Volume
 Uncontrolled Terms: Closed form solutions
 Subject Areas: Data and Information Technology; Highways; Materials; I32: Concrete;
Filing Info
 Accession Number: 01091535
 Record Type: Publication
 Files: TRIS
 Created Date: Apr 5 2008 3:04PM