Road Salt

Road salt is put onto roads in the winter to prevent ice from forming, or to deal with it once it has. When salt is added to water it decreases the melting point, so adding salt to ice that has just frozen will melt it. It may not stay melted for long if the temperature continues to drop, or if you do not keep adding salt. However, this is where the other ingredient of road salt comes in. Grit.

Grit is added to the salt and this provides a gripper surface to the road, preventing to some extent the development of dangerously smooth slick ice. Concrete road, bridges and tunnels can suffer extreme degradation in countries where road salt is routinely used in the winter. This is because the salt gets into the concrete and starts to corrode the steel reinforcement, the resulting rust expands creating cracks and allowing salt to infiltrate further. It used to be called concrete cancer, but the term is no longer used.