Progress in building materials analysis (Part 2)

15 C3S after 18 h hydration time: a) Helix detector image of the needle-like C-S-H phases in their native state; b) the same C-S-H phases imaged with too high charge density (damage to the C-S-H crystal structure – typical formation of bubbles)
15 C3S after 18 h hydration time: a) Helix detector image of the needle-like C-S-H phases in their native state; b) the same C-S-H phases imaged with too high charge density (damage to the C-S-H crystal structure – typical formation of bubbles)
16 Cryo-SEM: a) high content of K-sulfate OPC – 90 min hydr. time: ettringite and syngenite are detectable; b) low content of K-sulfate OPC – 40 min hydr. time: only ettringite and foil-like C-A-H phases are detectable – no syngenite
16 Cryo-SEM: a) high content of K-sulfate OPC – 90 min hydr. time: ettringite and syngenite are detectable; b) low content of K-sulfate OPC
– 40 min hydr. time: only ettringite and foil-like C-A-H phases are detectable – no syngenite
17 UHPC matrix with reacted silica fume particles (see arrows): a) Helix detector image at 0.4 mbar water vapor pressure; b) vCD – BSE-detector image: beam deceleration mode landing energy of the electrons 1.5 keV
17 UHPC matrix with reacted silica fume particles (see arrows): a) Helix detector image at 0.4 mbar water vapor pressure; b) vCD – BSE-detector image: beam deceleration mode landing energy of the electrons 1.5 keV
18 UHPC matrix with spherical shaped silica fume particles – uncoated sample imaged in LV-SEM mode at 2 kV: a direct comparison of a progressing pozzolanic reaction [a) Silica fume particle with signs of dissolution, b) respectively in its original state]
18 UHPC matrix with spherical shaped silica fume particles – uncoated sample imaged in LV-SEM mode at 2 kV: a direct comparison of a progressing pozzolanic reaction [a) Silica fume particle with signs of dissolution, b) respectively in its original state]
19 OIM analysis of a strained quartz: subgrains smaller than 10 µm are selected (see image small); these are color-coded in the map. 20  % of the entire scan area consists of these subgrains
19 OIM analysis of a strained quartz: subgrains smaller than 10 µm are selected (see image small); these are color-coded in the map. 20  % of the entire scan area consists of these subgrains















Reaction products of blast furnace slag (left) and silica fume particles
Reaction products of blast furnace slag (left) and silica fume particles

Summary: By means of modern electron microscopy and preparation technologies it  could be proved without doubt that the temporary syngenite formation during the early hydration of OPC with a high content of potassium sulphates is not an ESEM artefact. It can be derived from the microscopic investigations that the C-S-H phases occurring during the hydration process of OPC or C3S in the outer hydration rim always show the same needle-like habit and they have a crystalline nature. These C-S-H phases are very sensitive to radiation damage. Furthermore some applications of the integrated EDS-EBSD system for phase identification and orientation mapping for the subgrain crystal size determination are presented.

4 Results and discussion

In the following some examples are described relating to the manifold microscopic and analytical capabilities of the FEI Nova NanoSEM in combination with high-pressure cryo-preparation techniques. These methods are especially useful to answer fundamental questions on cement chemistry.

 

Are the C-S-H phases crystalline which are
formed during the OPC hydration?

The C-S-H phases formed during the hydration process at ordinary temperatures and for realistic water/cement ratios of C2S, C3S and OPC always appear in the same needle-like morphology when ESEM-FEG and NanoSEM...

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ZKG 02/2010

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ZKG 02/2010

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