Wednesday, August 03, 2016

Creepy concrete

I hadn't realized it before, but concrete bends or creeps under stress, albeit slowly. At least when it is outdoors.

The summary I linked is about a study looking at the effect of stress on calcium-silicate-hydrates. You can think of concrete as grains held together by calcium-silicate-hydrates. Put the whole thing under stress, and nearby grains will be pushed in slightly different directions, producing a force on the "glue joint." Add water ("aqueous solvent") and tiny amounts of the calcium-silicate-hydrates will dissolve.(*) Of course they'll precipitate out again too, but they will dissolve more readily from a stressed area, and precipitate out elsewhere. In effect, the grains and the matrix they are embedded in will slowly change shape--to a configuration with less relative force. Creep.

The stuff isn't very water soluble, so the change happens slowly. They still have to measure other factors--this might account for the known effects, or perhaps other things are going on too.

(*) You knew that glass was water soluble too, right? And quartz too--just not very. In some studies that matters. And it matters for growing agates.

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