Sidewalk question

Brain fart here.
What is the name of the material that gets stuffed into sidewalk expansion joints?

expansion joints are made out of what is called black board, or celotex, we called it expansion felt in my day.

Thanks Duke.
Inserting in a report because they need it.

I get those cramps also, you are welcome

Actually celotex does not appear to be the correct name so I simply recommended they fill the control joint and left material name open.

Still do not know as the web sites recommend concrete caulk.
What you said about it being called expansion felt makes sense but it looks as if they just use backer rod or urethane today.

Yepper, caulk at a control joint. Celotex I saw recently on a concrete site. New name to me. But I am getting up there.

I installed this stuff in my driveway expansion joints last year. Works great. Backer rod or sand needed to fill voids prior to using this product. Self leveling.

$50 for 29 ounces ,they must have some of Nicks gold mixed in.

This is interesting:

Too bad no picture though that may be the stuff.

Like the look but wonder how it ages?

Back in the day we called it impregnated celotex.

Thanks and I may also have been thinking of Oakum.