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Re: Carbonation

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Carbonation of concrete is a process by which carbon dioxide in the air penetrates the concrete and reacts with the hydroxides to form carbonates.  This can easily happen if you happen to be using heaters in a cold weather situation and you do not exhaust the fumes adequately.  Carbonation and rapid drying of fresh concrete may affect surface durability but is prevented by proper curing (or the opposite if you had poor curing).  Carbonation of hardened concrete does not necessarily harm the concrete matrix (in fact it can raise the surface concrete compressive strength) but it significantly lowers the alkalinity (pH) of the concrete which can cause accelerated corrosion of the rebar.  The surface of severely carbonized concrete can be almost slick and shinny which could effect the bonding of new concrete to old.

Thomas Hunt, S.E.

"Terangue Gillham" <tiger(--nospam--at)>
05/07/2008 09:07 AM
Please respond to seaint

I am trying to figure out what role carbonation may have played in a structure that has experienced debonding of a 2 inch thick concrete topping that was placed on 4 inch thick precast planks (roof structure).
I had a lab do analyses on a number of samples including ones in which the debonding had occurred and one sample where the topping and plank were still bonded.
The staining with the phenolphthalein indicator solution showed significant carbonation depths for the debonded topping and plank interface surfaces (debonded a while ago and carbonation occurred), but for the still bonded sample it showed carbonation on the top plank surface and NONE on the bottom topping surface.  In other words, the plank top surface appeared to carbonated prior to placement of the topping.
I am wondering if anyone has dealt with the effects that carbonation may have on the ability of fresh concrete to bond to a carbonated surface.  Would it reduce the potential bond, or have no discernable effect?
I’d welcome comments if you have any.


Terangue *Tiger* Gillham, PE
GK2, Inc.

tiger(--nospam--at) <
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