Not road salt?

About a month ago I passed a large truck spreading a white granular material on the roadway. I have always heard that Winnipeg doesn’t use actual salt on the roads, as it is usually too cold for it to work. So, what was this material being spread on the road? Whatever it is, it seemed to be effective at keeping the snow like a slurpee even at -12 C. It also seems to cause white stains and deposits in the interior and exterior of my car. What is it?