Poorly cured concrete starts its life with a defect that could be fatal. Water-filled voids, instead of filling with hydrated cement, remain empty after the mix water evaporates. Avoiding this handicap requires the engineer to specify adequate curing and the contractor to use curing methods that work.

WHAT IS CURING?

Curing maintains the moisture content and temperature needed for cement to hydrate.

HOW LONG DOES CONCRETE HAVE TO BE CURED?

The American Concrete Institute's Specifications for Structural Concrete for Buildings (ACI 301-84) gives several alternative requirements for duration of curing.

WHAT METHODS AND MATERIALS ARE USED FOR CURING?

Methods for maintaining the needed moisture content for curing fall into two categories: applying water continuously; and preventing excessive moisture loss. For many concrete jobs, curing compounds are the most economical curing method. Don't use them, though, on surfaces that are to receive a bonded overlay. Under most conditions, leaving forms in place is an acceptable curing method for vertical surfaces. Absorptive wooden forms left in place are not a satisfactory means for curing water containment structures during hot, dry weather. Under hot, dry conditions continuous wet curing is best. Wet burlap covered with polyethylene supplies additional water for hydration.