Concrete Driveway expansion joints

Old 06-03-09, 07:58 PM
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Concrete Driveway expansion joints


We live in Minnesota and have been getting bids for a replacement concrete driveway that will be 50 x 18.. My question is what kind of expansion joint should be install and how to be install.. Two different contractors said different things, one said by using a saw to cut in the expansion joint the other said while the concrete is wet you place them in.. Which is right?

Thank you
Old 06-04-09, 03:34 AM
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Both are right. You can do it either way. However, consider that the joint needs to be at least 1/4 as deep as the slab is thick. So for a 4" thick driveway, the joints need to be at least 1" deep.
Unless the guy who wants to tool them in is using a brand new 1" jointer, his joints are probably not going to be deep enough to be effective. It's easier to saw in a deep enough joint than to tool it in, especially if the wire or rebar reinforcement is too close to the surface. I saw cut all my joints. They are much more effective in my opinion. Just make certain that the sawed ones are placed as soon as the concrete is hard enough that the joints won't ravel (look all ragged from small rocks popping out when sawed). In 70 degree weather or hotter, this would probably be early the next day. Cooler temps may need to wait a bit longer. Don't wait too long though, or the concrete can exhibit shrinkage cracks before it is sawed. It's a fine line.
On a 50 x 18 driveway, there needs to be a joint up the center, and every 10 feet across the drive. You could also add an extra joint and make the sections 8' 4". That's what I'd do. Under no circumstances allow them to omit the center joint or cut the sections longer than 10'. If you do, you will certainly get cracks outside the joints.
BTW, they are not cutting expansion joints, they are cutting contraction joints. Expansion joints are joints filled with a compressible material. They should place expansion joint material wherever the new concrete butts up against a rigid surface such as a curb, garage floor, or brick or stone on your home.
Contraction joints are also called crack control joints and create a weak place where the concrete is likely to crack during drying shrinkage. Good luck.

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