Using fractal geometry to recover the 3D air void, scale-independent, microstructure information from 2D sections of mortars

Advances in digital image analysis have allowed for rapid and detailed investigations of themicrostructural topography of cementitious materials, and recent theoretical and analytical work have allowed for recovery of 3D information from2D analyses. However,measurements of parameters such as the entrained air void size distribution and number density obtained fromdigital images of concrete are sensitive to the resolution of the image. To address this, an analyticalmodel for recovering 3D information from2D sectionswas applied to images of air-entrainedmortar at different resolutions, and the results were interpreted in terms of fractal geometry. It is shown that there exists a "cutoff" resolution for scale independence, which is crucial for viewing stereological measurements in an absolute sense rather than relative to the resolution of the instrument used to acquire them. For the analysis of entrained air void structure, this cutoff resolution is around 3200 DPI; for such analyses, it is recommended that images be acquired at this resolution. Furthermore, the same analytical model was validated against full 3DX-raymicrotomographic images.