Placing Concrete Materials In Hot Weather

Construction workers directing the flow of concrete materials being pumped into forms that make up footers upon which the new foundation for the building will rest.

When does hot weather make placing concrete materials difficult?

Somewhere between 75°F and 100°F hot weather problems can become an issue for concrete materials. And without using the proper care, your pour may suffer from reduced strength and cracking due to drying too quickly. It can also stiffen too quickly making finishing a nightmare. The most problematic weather combination is low humidity with high winds.

Anything to remember before getting started?

Don’t forget to protect your crew from the elevated heat too. Make sure they drink and have plenty of fluids available, schedule frequent breaks in shady areas and constantly be on the lookout for signs of heat stress.

Is there a best way to keep concrete cool in the heat?

There are several ways to cool concrete, but the most efficient method is to cool the aggregates. You can do that simply enough by sprinkling water on them and letting the evaporation process do its magic. Other ways include using ice or injecting liquid nitrogen into the mixer, but both add cost. In any case, you should always be prepared to use sunshades, windbreaks and any other ways to prevent rapid drying.

How should you prepare for the concrete pour?

Have equipment and concrete supplies ready to use before hot weather arrives. Keep subgrade and forms moist so they won’t absorb water from the mix. Use sunshades and windbreaks whenever possible. Stay in constant contact with the ready mix concrete provider and have everything prepared before the mix truck arrives. Don’t make the truck wait on you.

What should be done after the concrete mix truck finishes pouring?

After placement, the concrete should be struck off and darbyed immediately. Be sure to use evaporation retardants, fogging or misting with water – or cover with a vapor-proof sheet before screeding. This helps prevent rapid drying, crusting, plastic shrinkage and rubber sets. Temporary covers like continuously moistened burlap can be placed over the fresh concrete and removed in small sections immediately ahead of the finishers.

Is there a best way to finish a hot-weather concrete pour?

You can eliminate high-risk practices like smooth trowel finishing by substituting a burlap drag or broom finish. Curing should happen when surfaces are hard enough to resist marring and sealing should be done with a good quality sealer a minimum of 30 days after the concrete has been placed and cured.

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