Frost damage to concrete step

[sueonmull]

I cast a 6" step about 3 months ago made up of 5 parts quarried aggregate (type 2) with dust to 1 part cement.
During the recent prolonged icy conditions this step was salted and the surface in the centre of the step has broken down to about a 1/2" depth. The sides and other areas of the step are unaffected. Is the problem related to the application of salt?
What is the best method of repair to make good and to give the step better resistance in the future. The step has a slight slope away from the house. There is also a drain channel between the step and the door threshold so the overhaul height of the step cannot be increased.
Thanks

 

[PrenticeBoyofDerry]

best means of repair, would be build some form work arond the step in question to the height you need and pour a concrete repair compound in to it.
I'd have put more cement in the original mix though.
But wait till the weather is milder.
Can't see why the salt would have caused this effect, likely frost has blown it.