Quantifying dispersion of nanosilica in hardened cement matrix using a novel SEM-EDS and image analysis-based methodology

A novel image analysis method integrated with SEM-EDS is proposed in this study for assessing the dispersion state of nanosilica (NS) particles in the hardened cement matrix. The method entailed capturing a statistically significant number of SEM micrographs of a cement-NS paste and their EDS elemental maps, the latter of which revealed that at 3-days, distinct C-S-H gel with a consistently low Ca/Si ratio (<0.9) had formed through pozzolanic reaction. Thereafter, pixels with Ca/Si ratio of 0.6-0.9 were extracted from a micrograph using a ternary plot of the atomic percentages of Ca, Si, and Al. Following this procedure, binary images were obtained, based on which, for the first time, the agglomeration and dispersion of NS particles in hardened cement paste were characterized using various quantitative descriptors, such as fractal dimension and Delaunay triangulation. A relatively small mean absolute error (1.16 vol%) validated the accuracy of the proposed methodology.