Cement: Difference between revisions
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Altilunium (talk | contribs) (Created page with "Portland cement consists of the following major compounds : tricalcium alumniate, tricalcium silicate (alite), dicalcium silicate (belite), tetracalcium aluminoferrite and gypsum. == Reactions == When water is added to cement, the following series of reactions occur * The '''tricalcium aluminate''' reacts with the '''gypsum''' in the presence of '''water''' to produce '''ettringite''' and heat (▲H = 207 cal/g). Ettringite consists of long crystals that are only stab...") |
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* The '''tricalcium aluminate''' reacts with the '''gypsum''' in the presence of '''water''' to produce '''ettringite''' and heat (▲H = 207 cal/g). Ettringite consists of long crystals that are only stable in a solution with gypsum.
* The '''alite''' is hydrated to produce '''calcium silicate hydrates''' (CSH), '''lime''' and heat (▲H = 120 cal/g). The CSH has a short-networked fiber structure which contributes greatly to the initial strength of the cement glue.
* Once all the gypsum is used up in the first reaction, the '''ettringite''' becomes unstable and reacts with any remaining '''tricalcium aluminate''' to form '''monosulfate aluminate hydrate''' crystals.
** The monosulfate crystals are only stable in a sulfate deficient solution. In the presence of sulfates, the crystals resort back into ettringite, whose crystals are bigger than the monosulfates (two-and-a-half-times). It is this increase in size that causes cracking when cement is subjected to sulfate attack.
* The '''belite''' also hydrates to form '''calcium silicate hydrates''' and heat (▲H = 62 cal/g).
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