Curing Methods and Materials
Concrete gains strength by the process of hydration, which is a cement-water reaction.
If concrete is allowed to dry prematurely, the reaction ceases. In this case, the strength is severely reduced and cannot be recovered even if the concrete is re-wetted. This is especially true on the surface of concrete.
Re-wetting dried concrete also causes cracking, especially on the surface.
Since any loss of moisture from the concrete will result in a loss of strength or surface cracking, proper concrete curing, regardless of the method used, should commence as soon as forms are removed or as soon as the surface will not be damaged by the curing method.
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Moist curing with water is ideal and is accomplished by keeping the concrete surface covered in water. This is done by using sprinklers, fog sprayers, or dikes. Water used for making concrete is suitable for curing, too.
Liquid membrane-forming compounds of various types can be applied to fresh concrete to help ensure that the concrete will not dry out due to neglect. Some of these compounds will discolor the concrete, and others will seal the surface for subsequent application of paint or floor coverings.
Mats and Blankets
Wet curing with cotton curing mats or moving blankets eliminates the need for continuous spraying. For winter concreting, commercial insulating blankets, fiberglass batts, or expanded plastic cell slabs can be used to protect the concrete from freezing; however, they generally must be protected from snow and water penetration.
Curing Paper or Plastic Sheeting
These products perform the same function as curing compounds and do not discolor the concrete. However, they must be weighted down and sealed at the edges to prevent water evaporation and wind damage.
Concrete Slump Testing
A slump test is used to determine the consistency of concrete, referred to as its flowability or workability.
The test is the distance, in inches, that the top of a conical pile of fresh concrete will sag after a standardized cone mold is removed.
Concrete slump must conform to the structure specifications.
Estimating Concrete Volume
Accurate measuring and estimating of concrete quantities is required for concrete work.
Fortunately, most concrete structures can be divided into rectangular or circular shapes, individually estimated, and the results added together to obtain the required volume of concrete.
For instance, a floor is a rectangular horizontal slab. A footing and a wall can be divided into a long rectangular (nearly square) shape representing the footing and a vertical slab representing the wall. The volume of each can be calculated and the results added together for the total volume.
Blueprints for a project will provide the dimensions or the various portions of a concrete structure, and these dimensions are used to calculate the volume of concrete required for the structure.
For reference purposes, the appendix provides area or volume for conversion of inches to fractions of a foot or a decimal equivalent.