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Recently a dip formed in our flooring inside our sports performance training facility. We discovered that the concrete job there had a good number of stones in it, and I believe that it was that combined with poor adhesion and cavitation that led to what you see at the following links:

I cleaned out all the larger 'stones', and am wondering if I can fix this myself. If I do, what will I need? What do I need to do to ensure that this doesn't happen again? We're a training facility, so the floor needs to be able to withstand some amount of impact.

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More pictures

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    Training facility is wonderfully vague. You train stenographers, typists, lions, acrobats, dogs, CCNA's, tomatoes? If you can track down the concrete contractor responsible, I'd start with making them fix it. – Ecnerwal Aug 3 '15 at 17:12
  • Couldn't have said it myself. I think this is indicative of a larger problem. Rarely have a see acute, isolated AND catastrophic failure of concrete. It's all mostly good, or it's all suspect. It's just a matter of timing. – BrownRedHawk Aug 3 '15 at 17:35
  • Sorry guys, sports performance. This hole is right next to our medicine ball wall, where the wall is subject to many impacts from balls over the course of the day. – Ellocomotive Aug 3 '15 at 18:20
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    I'm not an expert, but there's what looks like a drain inside. Given that, I think its likely that this occurred when the building was redone for our facility. – Ellocomotive Aug 3 '15 at 18:23
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Acquire a rotatory impact hammer drill so that you can pocket rebar into the existing concrete. Buy 'high-strength' expensive concrete. If you called a truck for onsite mixing (an unnecessary expense), tell the driver, 7 bag mix.

An alternative to rebar, for such a small patch, is to use long masonry screws, left standing proud to provide an anchor. E.g., use 3" screws, embedded a mere inch, using at least two per side (quarter inch diameter fasteners, minimum).

Knock down any sharp edges or small 'lips' in the hole, as it will crack along them later if you don't. I'd square off that part where it slopes down into the hole; it's not going to be thick enough there if you don't. Remove all unsound or lose concrete.

Before you pour, settle the substrate by soaking it with a garden hose. While you spray it, hit the sides of the old concrete to clean them of dust and debris. I like to slightly undermine what's there, so that it all locks in like a tetris piece. Wait until all standing water has dispersed.


There's what looks like a drain inside.

Insure the drain is 'properly' capped (plug it with empty concrete bags, leaving a little room for concrete and encapsulate the whole thing with your pour), this could be the root of the problem, or it's at least the reason a patch was slapped at it, in the first place. Do a better job anchoring it this time and you should be fine, even if the drain still weeps a bit.

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The big issue here is that it looks like you have about 3 inches of concrete sitting on sand. Sand is not a good foundation material. Don't you read the bible? Right in the bible it says:

Everyone then who hears these words of mine and does them will be like a wise man who built his house on the rock. And the rain fell, and the floods came, and the winds blew and beat on that house, but it did not fall, because it had been founded on the rock. And everyone who hears these words of mine and does not do them will be like a foolish man who built his house on the sand. And the rain fell, and the floods came, and the winds blew and beat against that house, and it fell, and great was the fall of it.

You can fill those holes with concrete, but your fundamental problem remains.

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    I don't think liquefaction is the problem here. – Mazura Aug 3 '15 at 21:53

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