Time-resolved combined SAXS and WAXS studies on hydrating tricalcium silicate and cement

Abstract

The objective of the experiments discussed here was to investigate the hydration process of the clinker minerals tricalcium silicate (C3S) and tricalcium aluminate (C3A) as well as that of ordinary Portland cement in the early stage of hydration (within several hours after the onset of hydration). Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) patterns caused by microstructural objects (nanometre and micrometre range) as well as by crystalline phases were observed at room temperature and at 40°C. Combined and time-resolved SAXS and WAXS studies in the early stage of hydration (until approximately 21 h) are reported. The experimental results indicate that two types of internal surfaces occurred simultaneously. Smooth surfaces, namely surfaces of Euclidean geometry, coexist with fractal surfaces. Analysis of different segments of a scattering curve showed that the proportions between Euclidean and fractal surfaces changed with time after the onset of hydration. A direct comparison of the structure-forming processes in the nanometre range at different temperatures (room temperature and 40°C) is given by the SAXS results. SAXS/WAXS, in addition to small-angle neutron scattering, represents one of the few relevant non-destructive test methods that provide undisturbed information about the nanostructure and microstructure of hydrating phases. The combination of SAXS and WAXS is a powerful tool for the simultaneous observation of X-ray amorphous (non-crystalline) and crystalline structures.