|
Peter:
Mas vale tarde que nunca. (Translation:
It´s better late than never)
The HEBEL support engineer here gave as
the following info:
All
cement-based materials are vulnerable to the attack of atmospheric carbon
dioxide In concrete due to
the scarce diffusion of gas in their interior; the effect is only
superficial. AAC is a lot more
permeable to air and it absorbs carbon dioxide easily, then the hydrated lime,
either from the cement free lime or from the Si and Al hydrates reacts with the CO2 forming
calcium carbonate:
Ca(OH)2 +
CO2--------CO3Ca + H2O
Carbonatization causes a decrease of
volume, denominated
"carbonatization contraction". If CO2 concentration is high, or the
exposure time is enough long, the contraction originates fissures. In AAC during the curing Ca hydrates react with
the sand Si forming highly stable tebermorite so "carbonatization contraction"
tends to be small. The
risk from atmospheric CO2 contamination is very low, but is not the case in a
combustion chamber or chimney.
HEBEL of
Germany recommends coating chimneys or smoking conduits with refractory bricks
to avoid carbonisation.
Other
point in combustion chambers is
permanent exposure to flames. AAC resists a flame temp of 1000 ºC 240 minutes without any loss of
stability. If exposure time is much longer, the combined water of moisturized
cement will evaporate, degrading the material
Regard
Roberto.
----- Original Message -----
Sent: Tuesday, September 03, 2002 3:01
AM
Subject: Fwd: Re: A note in AAC
Date: Tue, 03 Sep 2002 15:59:55
+1000
To: Roberto Escardó <robertoescardo@arnet.com.ar>
From:
Peter Verhaart <pverhaart@optusnet.com.au>
Subject:
Re: A note in AAC
Maybe you should do a test. Did the man tell you
what chemical reactions you could expect?
Peter Verhaart
At
18:56 02/09/02 -0300, you wrote:
Autoclaved Aerated Concrete
(AAC)
There was
a thread about AAC some weeks ago: An young engineer workinkg with us
contacted last week a local maker (under a licence from Hebel in Germany)
The sales technician was very collaborative and he quickly discouraged us
about using it for combustion chambers: AAC is atacked by
CO2!!!
(Big note in
Manuals: carefully protect any chimney made with AAC bricks with
refractory bricks - AAC dose not stand CO2 exposure) Pitty, it sounded as
a nice material for combustion chambers!!
Roberto
Escardó
| 
