Expanding Concrete for railing repair

We have a steel railing on our porch and stairs in front of our townhouse. There is a small hole (1-1.5" deep) in the concrete at the base of the railing. The railing itself is solid but does have a little movement at the base.
I've been told there is a type of concrete that expands when it dries which would make it perfect to patch this area. Basically, I need to fill the hole to make sure water does not leak in and make the situation worse. Eventually, this will affect the structural integrity of the railing.
Does anyone know of such a product and it's name?
Thanks Scott
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The name is hydraulic cement.
Though just patching this little depression is not going to fix the problem. It will most likely is not going to stay.
Cement based products don't like to stick to already cured concrete and there is a lot of force on that spot (most likely why it cracked in the first place).
Hydraulic cement is used to archer posts in concrete but you need to have about a foot and a half of it deep and an inch or so all the way around the post. The cement expands as it cures and locks the post in the surrounding concrete.
Depending on your situation you may have to dug out the concrete around the post and pour a fair amount around the post.
As an alternative you could wedge something around the post to keep it from wobbling and seal around the post with concrete caulk or Gray silicone.

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<< Basically, I need to fill the hole to make sure water does not leak in and make the situation worse >>
You're best bet is a two part epoxy. The adhesion to concrete is legendary. The usual provisos are clean, dry, etc. Just follow the label directions. Have a look at other concrete patch products at the industrial supply houses, Grainger, etc., and do some Google browsing. HTH
Joe
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