Hydration of Portland cements (PC) is a complex phenomenon caused by the presence of multiple
components with multi-length scale variability. To investigate this complicated process, state-of-theart
3D nanoimaging techniques with excellent spatial resolution and the ability to scan large fields of
view are required. In this work, synchrotron X-ray near-field ptychographic tomography is used to
study four cement pastes within 0.2 mm thick capillaries.
Synchrotron ptychotomography produces electron density and absorption coefficient tomograms that
facilitate the characterisation of amorphous materials. By achieving a spatial resolution of around 220
nm with good contrast, nanofeatures such as the density and spatial distribution of amorphous
constituents can be identified.
Key findings include the revelation that a seeded C-S-H gel has a lower density than a CaCl2 accelerated
PC paste. In addition, the density of the C-A-S-H gel in a PC blend containing metakaolin and limestone
decreases when limestone is present. These density variations are critical in estimating the space filling
in the paste.
C-S-H nucleation seeding results in a reduced inner/outer C-S-H gel ratio, with different average sizes
of high-density inner C-S-H gel found under different hydration conditions. Various additives, including
nucleation seeding admixtures and CaCl2, alter the water/cement ratio and the overall density of the
C-S-H gel. The addition of alkanolamine admixture increases C4AF hydration, resulting in the
development of amorphous Al-rich iron-silicate hydrogarnet, which affects C4AF dissolution. The
addition of limestone to the PC-MK blend changes the electron density of the C-A-S-H gel and increases
the production of amorphous monocarboaluminate-like components, which influences porosity
refinement.
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