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-   -   Line spacer gaps in concrete driveway and sidewalks - ok to fill up gap? (

daluu 07-24-2012 09:05 PM

Line spacer gaps in concrete driveway and sidewalks - ok to fill up gap?
I've observed that concrete driveways and sidewalks are built from segments of concrete poured out as square (or approximately square) blocks. So it results in narrow line spacer gaps between these concrete blocks that make up a sidewalk or driveway.

I just recently noticed some sidewalks have those gaps filled up with a thin layer of concrete. You see the line but no exposed dirt/gap. Others may have the gap with dirt filled in it over time.

I was wondering if it is ok to fill up such gaps with a concrete filler or are those gaps necessary for some kind of air "breather" for concrete and/or water to seep through to wet the soil underneath (like keeping soil around foundation not too wet or dry for soil expansion/compaction). I assume those gaps are just a result of how concrete is layed out and not needed for "breathing" or anything like that, but wanted to confirm.

cleveman 07-24-2012 09:16 PM

From time to time, you will see crews going down an interstate or highway with air compressors. They will clean out all the joints and re-fill them.

This is not so important with sidewalks, because they should be tilted 1/4"/foot to allow water to run off, and the control and expansion/contraction joints are all parallel with the tilt, so water runs off, not in and under.

It is very common in this climate to see 4 corners coming together and smashing each other up a bit because of the expansion. This is with 1/2" expansion joints. Maintenance won't keep up and the joints will be left open over winter. They will repeatedly fill with water and freeze/thaw.

Next a crew will come in to replace these "4 corner" areas which have by now become pot holes. They will cut a diamond out, remove it, and fill in with new concrete. Hopefully they leave expansion joints, maybe even doubled up to 1". Then the fun starts over again and sooner or later they too need replaced and maybe the whole parking lot is done next.

I suppose the solution is to have the entire surface set up to drain better from the beginning. It would also help to have a grade below which would provide for drainage.

To answer your question, yes it is a good idea to fill the joints with some filler. And in a freeze/thaw climate it is imperative.

Mort 07-25-2012 09:03 PM

The exposed dirt/gap you see is expansion joint material, a fiber. The other thing is a control joint, but they both accomplish the same thing, really. Concrete cracks, about every 10 linear feet or so, and those joints just tell it where to crack. The joints just look better than a crack, really.

Concrete needs to expand and contract, especially outside where it freezes, so you may have your filler crack too, and it'll look terrible.

Msradell 07-25-2012 10:20 PM

You can certainly fill those gaps. As Mort mentioned there is actually an expansion material in those joints. If you want to fill in the top of the joints to make things look better is not a problem but don't use concrete! Use a material of some type that will remain flexible.

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