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[SEAOC] RE: [SEAOC] Durability of Lightweight concrete

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On Thu, 5 Sep 1996 15:56:24 -0700  Estes, Kent R. wrote:

>wear surface, but this is no small cost.  Any thoughts out there on the
>durability of lightweight concrete to tire traffic?  The vehicle is
>comparable to a car or truck.  Is it a common practice for bridges that
>use lightweight concrete to use it for the wearing surface?

Well, I keep reading articles that proclaim the glories of lightweight concrete, but the few examples 
of it we've had here in Montana have performed abysmally.  That's hardly a definitive statement, but 
I know that I'd steer clear of it (no pun intended:-) for any traffic-bearing surface.

As far as repairs go, our standard practice for normal concrete is either to use a latex-modified 
portland cement concrete overlay or a polymer concrete overlay.  They both cost about the same 
amount, but the polymers save money as you don't have to raise expansion joints and the approach 
roadway grade to match the thicker concrete overlays, and the polymers save BIG bucks on traffic 
control because you can put traffic back on them in a matter of hours, instead of weeks.

In either case, you have to make sure that you remove all spalled and delaminated areas of the 
existing concrete before putting the overlay down, and you have to make sure you get all the rust of 
the rebars in those areas or the delamination will just recur within a year or two.  You also have to 
make sure you have good surface preparation before putting the overlay down or it won't stick.  Those 
decks made of lightweight concrete on which we've started the repair and patching process have been 
in such bad shape we've wound up having to replace the whole deck.

In the case of the polymers, you have to be careful which ones you use.  Some of them don't stay put 
very well.  So far (and we don't have a long history with them) the epoxies seem to work much better 
than the methyl methacrylates.  The latter have failed on roughly a third to half of the bridges 
we've put them on.

Nigel

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Nigel Mends, PE
email:  nmends(--nospam--at)mt.net
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