Hot weather can be defined as any period of high temperature in which special precautions need to be taken to ensure proper handling, placing, finishing, and curing of concrete. Other climactic factors such as high wind and dry air can also produce a rapid rate of evaporation of moisture from the surface of the concrete. Any combination of hot, dry, or windy weather can:
• Increase slump loss, through rapid surface evaporation.
• Accelerate set.
• Increase the potential of plastic shrinkage cracking.
• Decrease air content.
• Reduce strength, especially if water is added to offset slump loss.

High humidity can offset some of these problems.

Tips to Minimize the Effects of Hot Weather

• Contact your Prairie salesperson to discuss cooling concrete, reducing heat of hydration, and using a water-reducing, set-retarding admixture.

• Dampen the sub-grade, the forms, and any reinforcing steel to cool them

• Erect temporary windbreaks and sunshades.

• Consider early morning, evening, or nighttime concrete placement.

• Schedule ready mix trucks to minimize waiting time.

• Provide a sufficient work force to eliminate delays during construction.

• Protect the concrete between finishing passes.

• Apply final curing immediately after final finishing to control moisture loss and surface temperature.

• Saw cut the slab as soon as possible.

• Protect the surface; cover slab for at least 3 days.

Protection Between Finishing Passes

• Spray a "evaporation retardant" on the surface. This can reduce evaporation by up to 80% for concrete under shade and in windy conditions and up to 40% for concrete exposed to direct sunlight.

• Cover with white plastic sheeting or damp burlap.

• Produce a fog blanket by continuous fog spraying. Spray should not exceed ½ gallon per minute. Optional Fog Sprayer: Use a pressure washer that delivers 2 to 3 gpm at 2000 to 2500 psi, with a 40 to 50° wide-angle nozzle. In windy situations, use a 10 to 15° nozzle.