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hot weather concrete finishing

When pouring concrete, rapid set-up and drying can ruin your day. The warmer the day, the greater the danger of a quick set. Hot weather concreting can ultimately lead to accelerated curing and substandard strength. If you do not counteract the effects of excessive ambient heat before, during and after the pour, your concrete could deteriorate long before its expected service life. Here are 10 tips for hot weather concrete placement jobs.


1. Plan Carefully

Because you will need to incorporate some special procedures for your hot weather concreting, work out a plan in advance. Keep in mind that you want to place the concrete as quickly after it is mixed as possible. Make sure nothing on the jobsite will impede the delivery of the trucks or keep them waiting.

2. Beef up the Crew

You may need to increase your crew size so they can consolidate and finish quickly, particularly for mass flat work. Since summer daytime temperatures call for fast work, even small projects can benefit from extra hands.

3. Wet Ground, Rebar and Forms

In summer, the speed of hydration of the concrete will increase, especially as it comes in contact with excessively warm and dry ground, steel and form work. One way to keep these essentials cooler is to spray them down with just enough water to allow evaporative cooling without saturation.

4. Block Wind and Sun if Possible

When oppressive heat comes with no cloud cover, your crew would love a stiff breeze to cool them down. But with that breeze, your ideal concreting conditions blow away. Erect wind barriers to prevent the slurry from losing moisture to the dry Colorado wind. Providing shade may be a bit trickier, but tenting the area will certainly help the finishing process.

5. Chilled Aggregates and Cold Water in Mix

Since the addition of more water to extend the workable time will weaken the concrete, inquire whether your ready mix supplier will pre-chill their pile of aggregate and mix with very cold water. Replacing some of the water with ice can help considerably; however, if it hasn’t all melted in the drum by the time it arrives on site, it could come out as chunks, thus disrupting the uniformity of the mix and causing rejection of the finished product. Consult with the pre-mix supplier before accepting ice-cooled concrete. Always measure the temperature of the supply from the truck. You want it at or below 80 degrees with all ice melted.

6. Air Fogging

Fogging the air above the forms will reduce the ambient temperature over the pour without contributing water to the concrete. Acting as an evaporative cooler, the mist prevents rapid vaporization of the water in the concrete mix as it is poured and while consolidating and finishing.

7. Use Hydration Stabilizers or Fly Ash

Perhaps the most time-honored method for hot weather concrete projects along the Colorado Front Range is to use hydration stabilizers, water reducers or fly ash in the mix. Unlike the addition of extra water, stabilizers have no effect on the final strength of the concrete but allow you to work out the placement in a more reasonable amount of time while also properly pacing the hydration process.

8. Curing Compounds

Never wet the surface of a slab to buy time for a pretty finish. Watering the slab will weaken the finish and permit delamination, spalling and scaling, perhaps after only one freeze-thaw cycle. Additionally, to avoid shrink cracking, use curing compounds or cure-and-seal products after the crew completes the bull float work.

9. Use Blankets and/or Vapor Retarders

Slow vapor release with plastic sheeting or use the sun-reflecting white side of your concrete blankets to keep the surface cooler. The goal is to keep your concrete under 90 degrees while curing.

10. Pour at Night if Possible

With the cool nights along the Front Range, concrete working temperatures drop to just the right levels. If your client allows, and your supplier is willing, try placing at night or during very early mornings to avail yourself of the perfect temperatures without special admixtures or cooling techniques.

The Colorado Front Range may not see the blistering heat of places like Texas, Southern California or the Middle East, nevertheless, summer heat can take a real toll on your finished concrete projects. Take care to manage the mix and conditions at the site. If you need help determining how to proceed, please call Barton Supply for an expert opinion.