second layer of concrete over existing slab 1

[jrminator]

I'm considering the possibility of placing a 4 to 6 inch (reinforced) overlay on top of an existing (unreinforced) concrete driveway. The original driveway is badly cracked, because it wasn't properly reinforced. Standard practice here (Southeast US) is to break up the old concrete, haul it off and start from scratch. It seems to me that the existing concrete would make a decent sub-base for a new layer, as long as no water could get trapped in between. Concrete is not my specialty and this sort of thing isn't in any of the references or my old textbooks. Can anyone provide some technical guidance or a reference that might help?

 

[MotorCity]

If you wanted to leave the existing concrete in place, I would recommend breaking it into small pieces, maybe 2'x 2' (the smaller, the better) and seating them firmly in place. Sweep a granular material such as slag between the pieces to fill any voids. Then you could pour your slab on top. In terms of cost, it may be a wash depending on how much a contractor would charge to prep the slab as opposed to removing it. Another thing to consider would be elevation issues. For example, if your driveway and garage are at the same elevation and you increase the thickness of your driveway, there will be a step where the driveway meets the garage floor. Good luck.

 

[jrminator]

I appreciate the ideas. The original driveway follows the contour of the lot which is on a slope. The driveway slopes from the level of the garage to about 2 feet lower across the width over a distance of 20 feet. I am thinking about raising the driveway to an almost level plane by using gravel to give me a level surface for my pour. I can deal with the elevation difference at the garage by removing the existing concrete in that area. I had planned to do the formwork and prep myself, so the only additional cost will be for gravel (i don't know if slag is available here) which I haven't priced yet. A possible alternative to breaking up the old slab would be to drill a grid of holes to allow water to pass thru. Any additional thoughts?