Looks like your expansion joints rotted out.
Mason supply yards sell plastic expansion joints. They are two pieces. The top snaps into the bottom. Anyway use the top only and bang it into the gap. You may have to shave off the tabs but you want a snug fit.
I have done this before and it worked out well.

lets keep in mind that the OP is located in Utah where they can experience wide temperature swings from snow/ice in winter and elevated temperatures in summer.

I would be wary of putting any material in the joint that will interfere with the expansion/contraction of the individual segments

if you're heart set on filling the joint I'd suggest a non-rigid flexible caulk

Thanks for posting about this, 4x5...I've been meaning to do research on this for my driveway area.

I'm down here in Houston, so of course it's hot and humid 75% of the time and then cool and pleasant the other 25%. I share a common drive with the townhouses behind me, and that's the access to our garages...garages face each other. Most of the wood strips between the squares of concrete have rotted/broken away leaving a 3/4" to 1" gap. What is recommended to fill those voids?

I wouldn't care (but I do ), and every year or so, I power wash my "driveway" area and the area of some of my elderly neighbors. When I hit those cracks with 4,000psi, mud/dirt flies everywhere, especially all over me. Given our climate, can those areas be filled with some type of caulking? TIA!!

quote:

Originally posted by craigcpa:

quote:

Originally posted by mark60:
Backer rod with Sika Flex on top will work well.

My thoughts as well.

Yes agree, I have done this with my driveway.

Looks like there is lateral shift going on. Is the patio sliding down any slope of the yard?