Aggregate shape effect on the overestimation of ITZ thickness: Quantitative analysis of Platonic particles

• A methodology to construct the ITZ layer around Platonic particles is proposed.
• Systematic line sampling algorithm is used to estimate apparent ITZ thickness.
• The reliability of the generalized formula around Platonic particles is verified.
• Effects of particle shape and particle size are investigated.
• Overestimation of ITZ volume fraction and concrete diffusivity is evaluated.

Quantitative image analysis approach was often employed to obtain the apparent interfacial transition zone (ITZ) thickness around aggregate particles. However, the ITZ thickness may be overestimated via sectional plane analysis method, and exaggerate the ITZ's contribution to the macro-properties of cementitious composites. Until present, little work was done to derive the quantitative relationship between apparent and actual ITZ thickness, especially on non-spherical particle. This paper has proposed a methodology to construct the ITZ layer around Platonic particles and has employed a systematic line sampling algorithm to estimate the thickness of ITZ, called apparent ITZ thickness. The influence of particle shape unified by sphericity on the estimation of ITZ thickness unified by degree of overestimation is discussed where the degree of overestimation represents the ratio of apparent ITZ thickness to actual ITZ thickness. The particle shape effect is discussed for a single particle, for multi-dispersed spherical systems and for Platonic particle systems, respectively. Finally, the unexpected contribution of ITZ thickness overestimation on ITZ volume fraction and diffusivity of concrete are analysed.

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