Soft X-ray Ptychographic Imaging and Morphological Quantification of Calcium Silicate Hydrates (C-S-H)

Morphological details of calcium silicate hydrate (C-S-H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC-based systems but are still only partially known. Here we introduce the first soft X-ray ptychographic imaging of tricalcium silicate (C3S) hydration products. The results are compared using both scanning transmission X-ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C-S-H of fully hydrated C3S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high-resolution ptychrography image enables us to perform morphological quantification of C-S-H, and, for the first time, to possibly distinguish the contributions of inner and outer product C-S-H to the small angle scattering of cement paste. The results indicate that the outer product C-S-H is mainly responsible for the q(-3) regime, whereas the inner product C-S-H transitions to a q(-2) regime. Various hypotheses are discussed to explain these regimes.