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Re: Concrete disintegration[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Concrete disintegration
- From: GSKWY(--nospam--at)aol.com
- Date: Fri, 25 Apr 2003 09:53:01 EDT
There are an awful lot of things that can cause concrete disintegration. When it happens very soon after casting, it is usually something like the air-entraining agent dosage that was ten times as high as it should have been, due to a problem with the metering valve at the batch plant. This is something that can be established pretty easily by a petrographic examination. There is a machine that counts air bubbles in hardened concrete.
With respect to concerns about aluminum in concrete from the mixer or the pump line, this is not considered a problem as far as I know. Aluminimum is actually used as an expansive agent in most "non-shrink" grouts. The aluminum reacts with the alkalis in the cement to form little air bubbles. When properly dosed, you end up with a very small amount of air bubbles, when over-dosed, you get something that looks like hyperactive bread dough. It is sometimes used in precast construction for pour strips - usually a pre-mixed material is used, to avoid overdosage of the aluminum admixture.
The more common problem with aluminum in concrete is that when it is contact with steel, you get very severe galvanic corrosion. In this case though, it is an aluminum conduit or embed, in contact with rebar, not aluminum powder.
Aluminum is actually found in all portland cements as tricalcium aluminate (C3A).
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