You should avoid using typical rock salt, or sodium chloride, on your driveway. Rock salt is effective down to about -7 °C, but when temperatures drop lower, the melted snow will refreeze. This subjects your driveway to a higher frequency of freeze-thaw cycles, which can cause cracks to form or worsen existing cracks. Rock salt can also seep into concrete and speed up degradation of the metal reinforcement strengthening the driveway. The best rock salt alternative is shoveling your driveway diligently. Calcium chloride or magnesium chloride are effective alternatives if you still need to melt snow and ice.