Usually it follows gas prices and whatever is happening in china, when they built that big a$$ dam there was a huge shortage of cement. On a good 40-50 degree day I throw in a 1/2% and hot water to get things cookin. Most flat work is destroyed either by throwing salt on it within the first year or poor finishing, people will loose the pad and start getting too much water trying to bring it back to life, don't pour on a Saturday to avoid weekend charges and keep it over 4-6 yards to avoid a short load fee.