Replies

1. 
   Cameron_Duncan | Aug 23, 2001 07:13pm | #1

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   Joe,

   1. Try the Portland Cement Association for additional info.

   2. The reasons you stated certainly can induce cracking.

   3. If the pipe sleeve is aligned at right angles to the drive, you may choose to design in one or more expansion joint(s) (goes fully thru the concrete) or contraction joint(s) (sawcut or tooled) to aleviate future stress at this point. This may be done whether the drive is completely redone or only patched.

   4. Warrantee: The fact that this is an exterior issue, the timing of the occurrance, and the wording of the warrantee provided you often works against the homeowner in such cases.

   Cameron

1. 
   Mike_Shultz | Aug 23, 2001 09:36pm | #2

   *Joe,Since the pipe is intruding into the slab it acts like a control joint and creates a stress plane that allows concrete to crack at that location. A control joint, as defined by the American Concrete Institute (ACI), is 1/4 the thickness of the slab. So if your diveway is 5 1/2" thick any projection over 1 3/8" into it would create a crack potential. Your problem is that the top of the pipe is round and it does not create a single definable weak spot in the concrete but causes a larger weak area. This allows the concrete to have multiple jagged cracks above the pipe.The repair would be to make two saw cuts over the pipe and remove the spalled concrete. Brush the sides of the repair with concrete bonding agent and repour with grout. Add a "zip-strip" (plastic control joint) directly above the pipe to control the crack that will return.

1. 
   Mike_Shultz | Aug 23, 2001 11:08pm | #3

   *Joe,ACI 224 "Causes, Evaluation, and Repair of Cracks in Concrete Structures ACI 224.1R-93"ACI 332 "Guide to Residential Cast-in-place Concrete Construction ACI 332R-84"I am away from my office until Monday. I will check my ref. library for these.

2. 
   Joe_Laumer | Aug 23, 2001 11:08pm | #4

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   I live in a home that is 1 year old and have a problem with my driveway cracking. The crack is directly above a 4" PVC pipe sleeve that was installed to allow installation of irrigation lines. The sleeve was layed in a shallow trench and the concrete driveway poured directly on top of the pipe. One one side of the driveway there is 3" of concrete above the pipe, on the other side 2 3/4" of cover. My contractor's warranty does not cover cracks in concrete because "concrete just cracks". I understand that concrete shrinks and cracks as it cures. However, I feel the construction methods used in this instance (i.e.- inadequate concrete thickness over the pipe and no bedding or cover over the sleeve) are the reasons for the cracking, not the concrete material itself. Because of slight movement in the slab as you drive over it, the crack is starting to spall at the top and I believe it will continue to degrade over time, particulaly with the freeze/thaw cycles of winter. COMMENTS FROM ANY CONCRETE PROFESSIONALS?