It does not allow water to freeze, and makes ice melt faster.
First of all, what is gritting?
Those of you in cold countries where there is snow and ice must have seen it. Huge ‘gritting trucks’ go out in large numbers at night, to add something on the road. You will probably see the ‘grit’ on the roads the next day.
Although it is called gritting, there is actually no grit involved. Grit is small pieces of stone, pebbles and sand. But, gritting roads uses rock salt. Rock salt is similar to cooking salt, but it’s too rough and has too many other things in it, so we don’t use it for cooking.
How does it work?
For water to freeze, enough of its ‘molecules’ have to meet together and hold hands. (A molecule is too small for you to see, but it’s there is everything – it is the building block of things, same as bricks are used to make a building.)
When rock salt is added, water molecules keep meeting up with salt molecules instead of other water molecules. They cannot hold hands anymore, so water is unable to freeze and form ice.
Rock salt also interferes with ice. Ice is just water molecules, packed tightly together. Rock salt manages to get inbetween the molecules in ice, and breaks them apart, making ice melt.
So rock salt does two things: it prevents water from forming ice, and makes ice melt and form water again. Now you can walk safely on the roads, and people with cars can drive without skidding off the roads.