With the application of a three-dimensional (3D) characterization technique, serial block-face scanning electron microscopy (SBFSEM), the 3D microstructure of a hydrated cement monomineral, tricalcium silicate (C₃S), was measured with nanoscale resolution. The 3D morphologies of anhydrous particles, hydrated products, and capillary pores were visualized. Closed and open pores were discovered inside an anhydrous particle. The size and distribution of both the anhydrous C₃S particles and their capillary pores were analyzed quantitatively and the porosity was determined to be 9%. The distribution of pores was found to be in a good agreement with the inner and outer product model of Hu et. al., with an inner shell distance of 860 nm. Considering the spatial resolution of the instrument and the volume of sample measured, most pores in this experiment could be characterized as capillary pores.

A serial block-face scanning electron microscopy (SBFSEM) system, composed of a scanning electron microscope (SEM) and an ultra-microtome installed within the SEM vacuum chamber, has been used to characterize the three-dimensional (3D) microstructure of tricalcium silicate (C₃S) grains embedded in epoxy resin. A selection of C₃S grains were segmented and rendered with 3D-image processing software, which allowed the C₃S grains to be clearly visualized and enabled statistically quantitative analysis. The results show that about 5% of the C₃S grains have volumes larger than 1 μm³ and the average volume of the grains is 25 μm³. Pores can also be clearly seen in the biggest C₃S grain, the volume of which is 3.6 × 10⁴ μm³, and the mean volume and total volume of all the pores within this grain are 4.8 μm³ and 3.0 × 10³ μm³, respectively. The reported work provides a new approach for the characterization of the 3D spatial structure of raw C₃S materials, and the resulting 3D structure of the raw C₃S is important for further systematic research on the relationships between the spatial microstructure and the hydration kinetics of C₃S and other cement minerals.