Here are some of the most common causes of cracked concrete, and what you can do to prevent it.
1. Too much water. Extra water in the mix makes concrete easier to pour and work with. But it also weakens the concrete and makes it likely to crack. Concrete shrinks as it dries, so the wetter it is to begin with, the more it shrinks. Too much shrinkage, and cracking occurs.
2. Quick drying. The long-term (a week to a month) hydration process increases the strength of concrete, and will only work if the concrete stays moist. Cure the concrete by spraying on a liquid curing compound, which seals in the moisture, or by covering the slab with a cover, such as plastic sheeting.
3. Improper substrate preparation. You should remove all topsoil, compact the ground beneath and add a layer of gravel to promote drainage. This will help prevent the slab from cracking due to frost heaving.
4. No stress relief. You ever wonder why a sidewalk has grooves etched across it? These are control joints, which diminish the effects of the forces pulling on the concrete slab. And every so many feet, you’ll see an expansion or isolation joint, made from wood or a synthetic material. This allows individual slabs to move without causing stress.
5. No reinforcement. In some applications, particularly in driveways and structural areas, you’ll need to use wire mesh and/or rebars, which help increase the strength and durability of the slab.