With this highly effective curing box used by the Washington DOT, the cooler is partially filled with water to increase thermal mass and slow temperature changes.
Credit: Kenneth C. Hover
But even when the cylinders are gently moved to a safer place, ASTM C31-09, “Standard Test Method for Making and Curing Concrete Test Specimens in the Field,” requires “Immediately after molding and finishing, the specimens shall be stored for a period up to 48 hours in a temperature range from 60° F and 80° F [16° C and 27° C] and in an environment preventing moisture loss from the specimens. For concrete mixes with a specified strength of 6000 psi [40 MPa] or greater, the initial curing temperature shall be between 68° F and 78° F [20° C and 26° C].” Although there are a few jobsites in which the air temperature will not dip below 60° F nor rise above 80° F for a couple of days after casting (Waikiki in January comes to mind, but a field trip is required for verification), such limited temperature swings cannot generally be relied upon. Curing boxes therefore are required most of the time, winter and summer.