Greetings. This winter, I will be tasked to pour some cement footings, down in a crawl space and I'm guessing at the time that this will take place, the temperature will be anywhere between -5 to 20F. I had heard from a fellow contractor that when they pour concrete below freezing, they mix the concrete mix with a water/salt mixture. Any idea what the ratio is on this mixture and what type of salt these guys are using? Thank you ahead of time.