Investigation of spatial nano-structure development of the hardened C3S pastes by serial block-face SEM

Hardened tricalcium silicate (C3S) pastes cured for different times from 12 h to 28 days were studied by serial block-face scanning electron microscopy (SBFSEM) with the region of interest (ROI) of (2.0 × 104) μm3 and their three-dimensional (3D) spatial structures with a voxel size down to 16.6 nm × 16.6 nm × 20 nm were quantitatively analyzed. From these 3D images, the morphological characteristics of different components of the hardened C3S pastes in three-dimensions are observed directly, such as the connected pores and closed pores. Additionally, the degree of hydration and porosity of the samples are measured as well. Results show that the evolution of the degree of hydration reveals the high reactivity of C3S with water. The formation of the pore network is a complex process which includes not only the partition of the open pores but also the continued hydration of C3S in the closed pores, especially the newly formed closed pores during hydration. The quantitative analysis from SBFSEM measurements were compared with those from traditional TG-DSC and MIP, and it proves that SBFSEM has good applicability in the field of cement-based materials