Hairy mold on concrete?

A few weeks ago a pipe burst in my garage and had a slow leak (drips) which I didn't detect for weeks. The wall and a raised concrete area were soaked. I let a fan blew on that area for a few days. The wall (wood and drywall) seems to be dry.
Later on, little dots of dark mold grew on the paper on the drywall. These are easily removed with bleach.
But there are also white hairy mold growing out of the concrete! If I shine an ultraviolet light on them for a few days they disappear. If I remove the light they grow back. In some area the mold grow so dense it looks like coral reef in air.
It's very strange because firstly, I thought the concrete has dried. Secondly, other than water, what's there for the mold to eat?
I turn the uvc light back on. When the white mold disappear, I plan to clean that concrete area with bleach to see if that would prevent them from growing back when I remove the light. Is there a better solution?
I don't go examine that area very often to avoid unnecessary exposure to mold.
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Posting a hosted-site picture or two would help, but it might be efflorescence. Google it and click on the Images tab.
R
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On Wed, 12 Jan 2011 11:52:28 -0800, bob wrote:

You've probably still got moisture trapped in there which is slowly coming back out and allowing the mold to grow; I've had a similar problem in our basement with a small patch after rainwater got in via the wood- chute last summer. The concrete might seem dry at surface-level, but it doesn't mean that there isn't moisture deeper in which is finding its way back out via hairline cracks in the concrete.

I did mine with bleach (although at a quite low concentration), and the mold just came back a few weeks later. I'm going to get some concrete- sealing paint and try that, I think - it can be applied to concrete which isn't 100% dry and claims to contain stuff that inhibits mold growth, so it should kill the mold and prevent moisture which might allow more to grow.
cheers
Jules
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Does bleach kill the mold on the concrete, if it doesnt its effloresence not mold.
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