Curing concreteCuring concrete can be defined as a chemical process that ensures the hydration of cement in newly placed concrete. The curing process is part of the chemical reaction between Portland cement and water to hydrate the product, creating a gel that can be laid down only in water-filled space. It usually involves the control of moisture loss and the temperature affecting the hydration process. Concrete must be placed, ideally between 50 degrees and 75 degrees Fahrenheit, and this temperature must be maintained during concrete curing. The curing process is vital to quality and has a strong influence on concrete properties such as durability, strength, water tightness, resistance, volume, and freezing and thawing resistance.
Curing Concrete: Water Curing Methods
Curing concrete with water prevents excessive loss of moisture when the concrete is covered with a layer of water for a predetermined period of time. Curing concrete with water allows controlling the evaporation of moisture from the surface and the concrete gradually produces its chemical reaction that will eventually harden the concrete. Even if alternative curing procedures are used, it is desirable that certain amount of water curing is done. Water curing can be done using the following techniques:
- Immersion- Immersion curing is usually done in concrete testing for curing concrete test specimens.
- Ponding- Ponding is used to cure flat surfaces on jobs or controlled areas where water could be easily ponded.
- Fogging- Fogging is used in circumstances where the temperatures are above freezing and there is low humidity.
- Wet Covering- Curing concrete with wet covering is done after concrete has hardened sufficient enough where the covering will not damage concrete’s surface.
Curing Concrete: Membrane Curing
Curing concrete with membrane or plastic sheeting is the most practical and efficient way to cure concrete in today's construction industry. Sometimes water is unavailable to cure concrete or if done using an incorrect procedure can alter the surface finishing of your concrete product. Sometime adding water to a concrete that has not finished its setting process, could adversely affect the hydration process altering concrete’s properties. A minimum thickness is required to ensure adequate strength in the sheet; ASTM C 171 Sheet Materials for Curing Concrete specifies 0.01 mm. Concrete should be covered with a membrane, either plastic or chemical compound that will likely seal off the pores and retard the evaporation of water from concrete.
Two common types of membrane curing are:
- Plastic Sheeting- Curing concrete with plastic sheeting requires covering all exposed areas of the concrete as soon as possible without damaging concrete finish. When plastic sheeting is used over flat surfaces, such as pavements or slabs, it should extend beyond the edges of the slab at least twice the thickness of the slab.
- Membrane-Forming Curing Compounds- Curing compounds are chemical products usually sprayed directly over the concrete surface, and allowing it dry forming an impermeable membrane that retards the loss of moisture from the concrete.
Curing Concrete: Why and When
Curing concrete is required to allow a transitional and constant evaporation of water from the concrete mix. How soon should it start the concrete to be cured? It all depends on the environmental conditions in which the concrete was placed and whether it was placed in between forms, directly over ground, submerged in water, and others. The best practice is to cure the concrete shortly after the chemical reaction has started allowing the concrete to be hardened. Concrete should not be allowed to dry fast in any situation, and the curing conditions will likely are to be maintained during the first 24 hours or at least until the final setting time of cement has passed.