When shrinkage forces exceed the strength of the concrete, cracking develops. This is also true for non-deformable concrete pieces. Deformation cannot occur in the event of shrinkage. When the tension exceeds the strength of the concrete, these conditions cause internal stress, which leads to cracking. The severity of this effect increases with increasing temperature and humidity. Cracking can also be caused by other factors such as excessive traffic on road surfaces, heavy equipment driving over the structures, etc. The main method of repair for concrete that has cracked due to natural causes or environmental effects is replacement. For example, if your home's foundation is beginning to show signs of distress due to soil movement caused by underground water sources, then it may be time to replace your driveway or front yard with something more durable that will last longer. If the damage is limited to an individual block in a sidewalk or parking lot, simple patching can often fix the problem. However, if the damage extends across several blocks or beyond minor surface repairs, then new concrete should be used instead. Concrete that is damaged by corrosion from salt used to melt ice during winter months or by acid rain is often replaced entirely. Where possible, existing reinforcement should be preserved when repairing concrete, but sometimes this is not possible. In this case, new reinforcement should be installed so that the overall strength of the concrete piece is not reduced.