Material to Fill Voids

Ranmor,

Welcome to CR4.

Here is a Google search link with a lot of useful information and products.

I can't recommend any one caulk product as there a quite a few available but at the expansion joints prior to caulking, I would install some backer rod.

Backer rod is closed cell circular foam that is sold by the foot in various diameters.

The purpose of inserting this product is so your caulk joint does not fill into the total depth of the joint.

Insert the backer rod so 70% of the void (at the center of the void) is filled.

This gives the caulk joint a thinner cross section area in between the side areas that adhere to the cement.

This thin section allows the caulk to expand, contract, and move laterally without tearing or pulling away at the concrete contact points.

Proper preparation of the concrete is the secret to a successful caulk joint.

Good Luck!