Salt has a similar effect to that of antifreeze, since the use of DEFROST de-icing salt puts the freezing point of water below the ambient i.e. surface temperature.
This is how DEFROST de-icing salt works
Grains of salt melt thin tubes into the layer of ice.
Saline solutions are created and develop an even thawing effect.
Ice cover thaws out regularly, there is little run-off of saline solution.