A good ready-mix plant can prepare concrete with chilled aggregates and cold water (or even ice), plus admixtures to help prolong working time. Don’t add more than five or 10 gallons of extra water per truckload at the site.
Heat, sun, and wind are enemies during a midsummer concrete pour. Time your pour to take advantage of early morning or late evening shade.
Contractors slow down and need more breaks in hot weather, so double up on help to get the concrete off the truck while it’s still fresh. A load that’s 90 minutes old should be rejected.