Warm Weather & Concrete Construction: Not Always A Good Mix

March 30, 2017 Monica Devlin Comments

Beyond aesthetic blemish and durability concerns, cracked concrete also results in the loss of time, money and reputation for contractors. With warm weather on the way, Plastic Shrinkage Cracking is a real concern for concrete construction professionals.

Plastic Shrinkage Cracking in Warm Weather

Plastic Shrinkage Cracking can occur when the surface of concrete dries before it gains enough tensile strength to resist cracking. This particular type of concrete cracking is more likely to occur when high evaporation rates cause the concrete surface to dry out before it has set. As the temperature outside continues to rise during the warmer seasons, so does the risk of plastic shrinkage occurrence. This is because the risk tends to be greater when the difference between the concrete temperature and air temperature is large. In the spring and summer, these conditions can easily occur at a pour site where large areas are exposed to the direct sunlight and higher temps, while other pour areas remain shaded and experience lower temps. Concrete exposed to the sun can be significantly hotter than the air temperature.

"The best way to avoid plastic shrinkage cracks is to understand the susceptibility of the concrete mixture to cracking, monitor the jobsite conditions and take the necessary actions to minimize rapid moisture loss from the surface of the concrete.”
--Plastic Shrinkage Cracking, Concrete Contractor 4ConstructionPros.com

The National Ready Mixed Concrete Association (NRMCA) lists the following conditions that cause high evaporation rates from the concrete surface, and increase the possibility of plastic shrinkage cracking:

Wind velocity in excess of 5 mph
Low relative humidity
High ambient and/or concrete temperatures

Measuring the Pour Conditions at The Jobsite

The Kestrel 5200 takes the guesswork out of determining evaporation rate for concrete jobs. The Kestrel 5200’s Evaporation Rate calculator allows you to enter the temperature of your concrete mix (from a probe or IR thermometer), then measure conditions at the pour site. The Kestrel 5200 has the American Concrete Institute Evaporation Rate nomograph built in, and displays the Evaporation Rate right on screen with no calculation or error-prone interpolation. With that information in hand, decisions about additives to the mix or curing adjustments can be made, preventing costly plastic shrinkage cracks of the slab.

Check out the following video about how to easily and instantly measure Evaporation Rate with the Kestrel 5200.

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Monica Devlin