[Stoves] Fly ash cement, Curiosity.

ajheggie at gmail.com ajheggie at gmail.com
Sat Feb 7 13:32:14 CST 2015


[Default] On Sat, 7 Feb 2015 13:28:09 -0500,Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:

>It is however still a hydrating mix (sets with addition of water which is absorbed and converts the lime back into limestone).

Careful Crispin I think you are mixing up two different processes,
hydrating will be the re attaching of water molecules to the oxidised
ash. Typically I think it is silicates of aluminium which re absorb
their waters of crystallisation and it is the growth of these crystals
that causes setting before the lime reaction.  Lime is first slaked
from CaO to Ca(OH)2 and this gradually re absorbs CO2 from the air to
form the calcium carbonate again.

Either will presumably fail when heated past your 400C temperature. I
thought it was you who recently pointed out a successful cement and
clay mixture works because the clay particles vitrify as the water and
carbon dioxide are driven off and hence hold the matrix together?

AJH




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