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The subgrade is as important as the concrete itself. It should be uniform in dampness, firmness, and grade. Dampening keeps moisture from being drawn to quickly from the concrete which helps to prevent cracks and discoloration. You want consistent dampness with no standing water. The subgrade should consist of a few inches of compacted granular fill such as sand, crushed stone, or pea gravel.
The normal thickness is 3 ½ to 4 inches. This is sufficient when the driveway is used only for cars. For heavier vehicles such as trucks and RV’s, the concrete should be 4 ½ to 5 ½ inches thick.
Reinforcement such as rebar and wire mesh can be used to hold concrete together but will not prevent cracks. Rebar is especially important where trenches or holes were dug for utilities.
The driveway should slope away from permanent structures at least an 1/8 inch per foot. If this isn’t possible, then a drainage system should be installed to control the flow of water. You don’t want water to stand on the driveway, especially where it could freeze.
Control joints are placed to give the concrete a suggested place to crack. Every driveway will crack. The control joints will hide the cracks or make them less noticeable. They can be cut into the driveway with a groover during finishing or the following day with a saw and diamond blade. The joints should be placed no more than 12 feet apart for a 4 inch thick driveway.
These are just some of the basics of installing concrete driveways. There’s much more to it and should only be done by experienced contractors.
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