The analysis of nanocrystalline and amorphous phases in cement matrices which
contain high amounts of crystalline phases is a very challenging task. In this respect,
pair distribution function (PDF) methodology in combination with synchrotron radiation
is very useful to characterize cement pastes. PDF data can give insight about the
atomic local structure of the non-crystalline components such as C-(A)-S-H gels. This
work is focused on the characterization of amorphous and nanocrystalline gels which
are present in cement related pastes by total scattering PDF analyses in selected
samples. In addition, the PDF approach also allows us to perform quantitative analysis
in order to know the nanocrystalline and microcrystalline contents. [1]
X-ray scattering data of different pastes were collected in BL04-MSPD beamline at
ALBA Synchrotron (Barcelona, Spain). Three sets of hydrated samples have been
studied and they will be reported: (i) tricalcium silicate, Ca3SiO5, the main component of
Portland cements; (ii) dicalcium silicate, Ca2SiO4, the main component of belite
cements; and (iii) tricalcium silicate samples mixed with different amounts of silica fume
(as the simplest example of supplementary cementitious materials). For all the PDF
analyses, a multi r-range approach was followed (see Figure below): the higher r-range
(e.g. 40-80 Å) is used to determine the microcrystalline phase contents, for instance,
portlandite and anhydrous phases; then, the intermedium r-range allows characterizing
the atomic ordering in the nanocrystalline fraction of the C-S-H gel (e.g. 10-40 Å); and
finally, the low r-range, below 10 Å, gives information about the chemical nature of the
additional amorphous components [2].
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