AVR, Inc. - Evaporation Rate Calculator

Plastic Shrinkage Cracking can occur when the surface of concrete dries before it gains enough tensile strength to resist cracking. The calculator below may be used to approximate the Evaporation Rate at the surface of a concrete placement. Hot Weather Recommendations may be found below the calculator.

This calculator relies on accurate data provided by the user and does not factor in other variables that can affect the speed at which a particular concrete mix will cure. As such, it should be used as a general guideline only.

Evaporation Rate Calculator

Average Wind Speed * mph [ Range: 0 to 40 mph]
Humidity** % [ Range: 0 to 99%]
Air Temperature** °F [ Range: 30 to 125° F]
Concrete Temperature °F [ Range: 30 to 99° F]

*Wind speeds should be measured at an elevation of 20 inches above the concrete and averaged.
**
Air Temp. and Relative Humidity should be measured in the shade, upwind and 4' to 6' above the concrete.

Hot Weather Recommendations

Hot weather can be described as any period of high temperature in which special precautions need to be taken to ensure proper handling, placing, finishing and curing of concrete. Hot weather problems are most frequently encountered in the summer, but the associated climatic factors of high winds and dry air can occur at any time, especially in the Fall in Minnesota. ¹

The three most common effects of hot weather concreting are crazing, plastic shrinkage cracking and drying shrinkage cracking.

Crazing is a pattern of fine cracks that do not penetrate much below the surface and are usually a cosmetic problem only. NRMCA Concrete in Practice #3: Crazing Concrete Surfaces

Plastic shrinkage cracking can occur water evaporates from the surface of freshly placed concrete faster than it is replaced by bleed water. NRMCA Concrete in Practice #5: Plastic Shrinkage Cracking

Drying shrinkage is the most common cause of concrete cracking. Because almost all concrete is mixed with more water than is needed to hydrate the cement, much of the remaining water evaporates, causing the concrete to shrink. NRMCA Concrete in Practice #4: Cracking Concrete Surfaces

AVR, Inc. recommends the following practices to reduce the effects of hot weather on concrete:

Pour during cooler temperatures, such as early morning or at night.
Don’t get too spread out – Have enough manpower to quickly place, finish and cure the concrete.
Moisten the subgrade and form work prior to concrete placement.
Limit the effect of wind and sun by using windbreaks and sunshades.
Use a superplasticizer, if needed, for a concrete consistency that allows rapid placement. Try not to add water – more water = more potential for cracking.
Prevent loss of surface moisture from the plastic concrete through use of evaporation retarders.
Ask our Dispatch Department about using synthetic fibers to help control plastic shrinkage cracks.
Provide the AVR, Inc. recommend curing methods as soon as possible after the concrete finishing processes have been completed.

References

ACI 305, “Hot Weather Concreting,” ACI Manual of Concrete Practice, Part 2. American Concrete Institute, P.O. Box 19150, Detroit, Michigan 48219.