Hot Weather Concreting; Setting And Curing Concrete

Concrete And Hot Weather

Setting And Curing Concrete

You can ensure success in hot weather concreting. Depending on the temperature concrete will set in anywhere between 2 to 19 hours. For example, if the temperature is higher than 100 degrees Fahrenheit, concrete is likely to set in less than 2 hours. If the temperature is in the low 40’s or high 30’s, concrete is likely to set around the 17 to 19-hour mark. Concrete will not set in any temperatures below 30 degrees Fahrenheit.

Keep in mind that setting is not the same as curing. Setting means the concrete has reached a completely solid-state, but still needs time to reach its full strength. Typically, concrete reaches 70% of its strength within seven days. After 28 days concrete is considered to be fully cured and at 100% strength. 

The way concrete sets is quite fascinating. It sets by sucking up water and forming crystals around the particles in the concrete. The cooler the concrete, the longer this process takes and the more time the crystals have to form and strengthen. However, when the concrete is hotter, the crystallization process happens more quickly, which doesn’t give the crystals adequate time to reach peak strength. This makes for weaker concrete that is more susceptible to cracking. 

Effects Of Hot Weather On Concrete

When exposed to extremely hot weather concrete can become compromised. Here is a list of weather’s effects on hot weather concreting:

  1. Resistance to weathering is decreased.
  2. The dimensional stability of the concrete is reduced.
  3. The strength of the concrete decreases significantly: The cooler the concrete, the longer it takes to set, and the more time crystals have to form and strengthen. However, when the concrete is hotter, the crystallization process happens more quickly, which doesn’t give the crystals adequate time to reach peak strength. This makes for weaker concrete that is more susceptible to cracking and crumbling. 
  4. Cracking can occur: To offset high temperatures, more water is generally required to maintain workable consistencies. However, high water contents also means greater drying shrinkage which leads to cracks. 

Precautions To Take When Hot Weather Concreting

The precautions taken depend on the actual conditions during concrete placement. The general rule of thumb is that if the temperature at the time of placement exceeds 77 degrees Fahrenheit, then a plan should be put in place to negate the effects of high temperatures. With proper planning and execution concrete can be successfully placed and finished at temperatures of 95 degrees Fahrenheit or more.

Hot Weather Concreting Precautions may include some or all of the following:

  1. Moisten the subgrade, reinforcement, and forms prior to concrete placement. 
  2. Place sunshades over concrete that has already been placed, this helps in reducing surface temperatures. 
  3. Reduce the initial temperature of the concrete mixture by cooling the water added to the concrete mixture. 
  4. Provide enough labor to decrease the amount of time spent on placing and finishing the concrete. 
  5. Consider adjusting the time of concrete placement to take advantage of cooler temperatures (i.e. pour early in the morning or late at night.)

Call JJ Kennedy Today! Although it comes with challenges, pouring concrete during warmer weather months is still possible. Using the tips above should ensure your concrete jobs go off without a hitch. At JJ Kennedy, we have the knowledge and experience to make sure that your concrete projects are done right the first time. To learn more, call 724-452-6260.

You can also visit us at any one of our 8 locations for Ready-Mix Concrete, Builders Supplies, Block & Material Delivery, Keystone Retaining Walls, and more: Clarion, Clarks Mills, Imperial, Indiana, Kittanning, Punxsutawney, Ridgeway, Zelienople

We have been providing concrete in Pennsylvania, Ohio, and West Virginia since 1905 with the highest standards of concrete quality assurance.

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