|
Hydration
Product of Tricalcium silicate : C3S
|
Hydration Product of Dicalcium silicate : C2S
|
|
|
|
|
Hydration Products of Tricalcium aluminate : C3A
(Ettringite & Monosulphate)
|
|
|
Ettringite:
The reaction of tricalcium aluminate with gypsum gives needle-like crystals
of a hydrated sulfate tricalcium aluminate called ettringite.
• Needles interlock, take up much water
• contributes to stiffening of mixture
• some early strength
|
|
|
Monosulfate:
Hexagonal plate morphology arranged in “rosettes”
during early hydration
• become more “platey” with
continued hydration
• can contain impurities
• vulnerable to sulfate attack
|
|
Hydration
Product of Tetracalcium aluminoferrite: C4AF
|
Picture showing plates of
Calcium Hydroxide (typical hexagonal habit) and the needle-like habit of
ettringite
|
|
|
|
|
Image of fracture surfaces of hardened cement
paste showing a platy, or foil-like, calcium silicate hydrate (CSH)
slender fibers of calcium silicate hydrate and, along the base of the image,
calcium hydroxide (CH) :platy habit.
|
|
|
|
Image of hydrated cement paste showing
calcium silicate hydrate (CSH), calcium hydroxide (CH) & Ettringite
|
|
|
|
Image of hydrated
cement paste showing calcium hydroxide (CH), unhydrated cement
& Capillary pores
|
|
|
|
Sketch showing structure of hydrated
cement paste
|
|
|
Calcium Silicate Hydrates exist in a variety of forms like fibrous particles,
flattened particles & a reticular network. The predominant form is that
of fibrous particles, possibly solid, possibly hollow, sometimes flattened,
sometimes branching at the ends. Typically they are 0.5-2µm long and less
than 0.2µm across.
Unfortunately, the structure of Calcium Silicate Hydrates is too
disorderly to be established by the existing techniques, including those like
scanning electron microscope & dispersive X-ray spectrometer.
Ca(OH)2 liberated by hydrolysis of the calcium silicates forms thin hexagonal plates, often tens of µm across, but
they later merge into a massive deposit.
Tricalcium aluminate hydrate forms a prismatic dark
interstitial material, possibly with other substances in solid
solution and is often in the form of flat plates surrounded by the calcium
silicate hydrates.
|
