Direct three-dimensional observation of the microstructure and chemistry of C3S hydration

Abstract

Disagreements about the mechanisms of cement hydration remain despite the fact that portland cement has been studied extensively for over 100 years. One reason for this is that direct observation of the change in microstructure and chemistry are challenging for many experimental techniques. This paper presents results from synchrotron nano X-ray tomography and fluorescence imaging. The data show unprecedented direct observations of small collections of C3S particles before and after different periods of hydration in 15 mmol/L lime solution. X-ray absorption contrast is used to make three dimensional maps of the changes of these materials with time. The chemical compositions of hydration products are then identified with X-ray fluorescence mapping and scanning electron microscopy. These experiments are used to provide insight into the rate and morphology of the microstructure formation.

Direct measurements of 3d structure, chemistry and mass density during the induction period of C3s hydration

“…Some sedimentation (bleeding) could occur in the sample with w/s = 5 during the experiment, but the results provide an average w/s that matches the nCT experiments. The details of these experiments are given in a previous publication [44]. …”

“…IPA was used because it has been suggested previously to have the least impact on the microstructure of hydrated samples [45,46]. Previous work with these same materials and techniques has indicated no observed differences in the microstructure before and after using IPA to stop hydration [44]. The cup was then lowered and the sample was placed back on the nCT scanner to obtain the final tomography scan.…”

“…The nCT and nXRF data are aligned by comparing 2D radiographs to match the particle boundary and areas of uniquely identifiable chemical composition. Additional details about nTACCo are provided in earlier publications [31,44]. …”

A critical comparison of 3D experiments and simulations of tricalcium silicate hydration

“…The experimental data reported in this paper have been published in a previous paper with full details on the procedures used [18]. A brief summary of the procedure is provided here.…”

“…The particles remained submerged for 7 h, after which the seal was removed and hydration arrested by solvent exchange with 99 % isopropyl alcohol (IPA) for 5 min. IPA was used because it has been shown previously to cause no observable differences in the C−S−H morphology or other aspects of the microstructure of hydrated specimens [18]. …”