1. Maintaining Moisture
Ponding and Immersion
Ponding is typically used to cure flat surfaces, such as pavements and floors, as earth and sand around the perimeter of the concrete surface can retain a pond of water. Ponding is an ideal method for preventing loss of moisture from the concrete; it is also effective for maintaining a uniform temperature throughout the concrete. Immersion of a finished concrete element is commonly used for curing test specimen.
Spraying and fogging
Spraying and fogging are used when the ambient temperatures are well above freezing, and the humidity is low. Fog mist is applied through nozzles or sprayers to raise the relative humidity of the air over flatwork, thus slowing evaporation from the surface. Fogging is used to minimize plastic shrinkage cracking. If sprinkling is done at intervals, the concrete must be prevented from drying between applications of water by using burlap or similar materials; otherwise, alternate cycles of wetting and drying can cause surface cracking.
Saturated wet coverings
Wet coverings saturated with water, such as burlap, cotton mats, rugs, or other moisture-retaining fabrics, are commonly used for curing. The materials should be placed as soon as the concrete has hardened enough to prevent surface damage. They should be kept constantly wet so that a film of water remains on the concrete surface throughout the curing period.
Left in place forms usually provide satisfactory protection against moisture loss for formed concrete surfaces. The forms are usually left in place as long as the construction schedule allows. If the forms are made of wood, they should be kept moist, especially during hot, dry weather.
2. Reducing Loss of Water
Covering concrete with impervious paper or plastic sheets
Impervious paper and plastic sheets can be applied on thoroughly wet concrete, such as polyethylene film. This material is a lightweight, effective moisture retarder that is easy to apply. During placement, the concrete surface should be hard enough to prevent surface damage.
Applying membrane-forming curing compounds
Membrane-forming curing compounds are used to retard or reduce evaporation of moisture from concrete. They can be clear or translucent and white pigmented. White-pigmented compounds are recommended for hot and sunny weather conditions to reflect solar radiation. Curing compounds should be applied immediately after final finishing and must comply with ASTM C3094 or ASTM C13155.
3. Accelerating Concrete Strength Gain
Live steam and high-pressure steam are the two methods of steam curing. The temperature for live steam should be kept at about 140 degrees Fahrenheit or less until the desired concrete strength is achieved.
Heating coils are usually used as embedded elements near the surface of concrete elements. Their purpose is to protect concrete from freezing during cold-weather concreting.
Electrical heated forms or pads
Electrical heated forms or pads are primarily used by precast concrete producers.
Concrete insulation blankets are used to cover and insulate concrete surfaces subjected to freezing temperatures during the curing period. When using concrete blankets, make sure that the concrete is hard enough to prevent surface damage.
Read the article about the importance of curing.