Hot Weather Concrete
When you get a concrete delivery in hot weather the concrete problems are mostly to be concerned about in summer, but some can happen at other times also. If the temperature is moderate but the air has little humidity it could call for a higher water demand or if there is a dry wind blowing across the surface of the slab it could cause quicker than normal evaporation of the bleed water causing plastic shrinkage cracks.
When in doubt always use hot weather practices. Think about if the humidity has been low, if the wind will be blowing more than five miles an hour across the surface of the concrete. Has the ambient temperature been high. Do you know your ready mix supplier’s yard? Does their aggregate sit in the direct sun? Are their cement silos in the direct sun? Will the truck be sitting in traffic causing a delay in getting to you and keeping the mix in the truck longer than normal? Try to think of anything that will cause the mix to heat up, increase water need or make the mix set quicker than normal.
If you decide to do the slab in hot weather conditions, make sure there is plenty of help on hand to get the mix off of the truck, placed and finished as quickly as possible. Make sure there is a water reducer in the mix when you put your order in. You might consider having them put a retarder in the mix instead of just a water reducer. The retarder will slow the set time and act as a water reducer.
If there is to be a vapor barrier under the concrete slab make sure there is three to four inches of material on top of it so all of the bleed water is not forced through the surface. Just before placing the mix spray water on the subgrade and forms to moisten them but do not leave any puddles. Start curing as soon as possible.