What do you place in the expansion joints when the original wood has rotted out?

The wood in the joint where the driveway meets the garage has rotted out. I figured I am supposed to put fir strips in there as a replacement but then what would hold them in place? The joint and the wood aren't even close in size.

Answers:
they make a injectable exspansion rubber that come in a tube to be used in a caulking gun.it comes out of the tube soft,but hardens with the curing process.home depot will be the best bet to grab yourself some.

Other answers:
Find some strips that are closer in size and wedge them in there. The pressure will keep them in place.
Find some strips that are closer in size and wedge them in there. The pressure will keep them in place.
try a mastic type silicone. as it will fill your joint but will allow movement also.
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