Salt Rock Foundation Driveway

We have a rock salt finish porch, driveway and sidewalks. These are the issues we are experiencing. First, we find when people walk in from outside from any of these areas they leave white foot prints. Second, we have alot of discoloration in the concrete. We know its not from water as the places where water sits doesn’t have stains. Its not fertilizer either because we don’t use it. Thirdly, we have areas where the gravel is sitting on top with no concrete top and we also have alot of large looks like machine brush marks. We appreciate all your help.