Cracks in new garage floor

I have a 24X24 garage floor that was poured in September of 2003. A new garage has been built on it and as I was about to clean the floor I noticed cracks in the expansion joint that runs from the center of the slab toward the back. The floor was troweled into four sections and the crack extends from the front back to where the four points meet in the middle.
The cracks range in width of about 1/32 to maybe 1/8. I plan on filling them with something to prevent water entry, but my greater concern is should they be cracking already?
I live in Wisconsin. Temps havent been much lower than 20's for any real length of time, fwiw.
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The cracks sound like they may be a result of concrete shrinkage. I doubt that temperature caused the cracking. Could be many factors that contributed to the cracking.
Was there rebar or wire used in the slab? Were alternate wires or rebar cut at joints. Was rebar or wire lapped at the joints? Was Fibermesh used? Did the contractor tool or sawcut the joints? How soon after the pour was the floor sawed? How deep was it sawed? How thick is the slab? How was it cured?
If the slab was 4" thick, control joints should have been placed at about 8 foot on center.
Jim K.

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If the cracks are spreading apart I would be cocerned of the quality of the installation! The floor will get hair line cracks, but they should not spread open. Was any rebar or wire mesh used? My garage is about 15 years old. The floor has a few cracks, but the are all tight. Greg
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"I noticed cracks in the expansion joint... " I believe that is the reason for the expansion joint.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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JT wrote:

The expansion joint is doing it's job - it's virtually impossible to keep a concrete slab from cracking with thermal expansion. The joints are there to help control the cracking in a controlled manner. If the cracks are fine 1/16" or so, I wouldn't worry about it.
Michael
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I mis- read the original post.
The joints are put in the slab to weaken it and to cause the cracks to occur at those locations (so they are reasonably straight and not random). Joints (tooled or sawed) are called control joints and those along walls that contain asphalt impregnated fiberboard (black) are called expansion joints.
I would not be concerned if cracks show up in the control joints. They are doing just what they were intended to do.
Jim K.

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Two types of concrete, 1. The kind with cracks; 2. The kind that is going to crack! You have the first kind.
Mike Coonrod
JT wrote:

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