First world problems... all the wood has rotted in the joints on my driveway. Leaves, dirt, etc... fill them up and leave a mess. I bought some backer rod and self-leveling caulk and the cost was about $20 to fill 5 feet - I have about 140 feet total. I found something else called slabgasket, but the prices is going to be $450.

A treated piece of 1X2 doesn't work because it doesn't fit into the gap.

Any other suggestions?

How deep of a sealant joint are you laying?

https://trim-a-slab.com/

buy the big tubes of the self leveler (30oz). It's 3x the size, but only about 50% more in cost. You'll need a caulking gun than can hold the big tubes.

Small one $8.45 for 10oz

Big one $11.97 for 30oz.

I think I'll try the trim a slab. Thanks for the comments

Bumping this, need to take this project on. Slab gasket or silicone?

Same. Bought backer last week. Plan to use self leveling and put some play sand in it to make it blend better.

You really only need 1/2" depth of sealant at the most. You can use clean sand to fill the joint to ensure you aren't loosing sealant past the backer rod.

Remove the wood and fill with concrete. The expansion joints aren't needed. It's a terrible design.

Or fill to about 1/2 the width with sand/ fiber/ etc and use silicone.