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The length of adequate curing time is dependent on the following factors: - Mixture proportions - Size and shape of concrete member - Ambient weather conditions - Future exposure conditions Slabs on ground e.
American Concrete Institute ACI Committee recommends a minimum curing period corresponding to concrete attaining 70 percent of the specified compressive strength. The often specified seven-day curing commonly corresponds to approximately 70 percent of the specified compressive strengths. Care should be taken to maintain curing water temperature at not more than 20 degrees Fahrenheit cooler than the concrete to prevent cracking due to thermal stresses.
Immersion is mainly used in the laboratory for curing concrete test specimens. Spraying and fogging Spraying and fogging are used when the ambient temperatures are well above freezing and the humidity is low. Fogging can minimize plastic shrinkage cracking until the concrete attains final set. Saturated wet coverings Wet coverings saturated with water should be used after concrete has hardened enough to prevent surface damage.
They should be kept constantly wet. Left in Place Forms 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. The concrete surface should be hard enough to prevent surface damage from placement activities.
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. Steam temperature for live steam at atmospheric pressure should be kept at about degrees Fahrenheit or less until the desired concrete strength is achieved.
Heating coils 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 blankets Concrete insulation blankets are used to cover and insulate concrete surfaces subjected to freezing temperatures during the curing period. The concrete should be hard enough to prevent surface damage when covering with concrete blankets.
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