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ACI Spring 2010 Convention
March 21 - 25, 2010
Marriott Rivercenter Hotel & Henry B. Gonzalez Convention Center -- San Antonio, TX

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April 12 - 15, 2010
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June 6 - 9, 2010
David L. Lawrence Convention Center - Pittsburgh, PA

ACI Fall 2010 Convention
October 24 - 28, 2010
The Westin Convention Center -- Pittsburgh, PA

 
Chapter 4 - Producing Silica-Fume Concrete
Preventing Plastic-Shrinkage Cracking

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Slide
This chart, which is found in both ACI 305R-91, "Hot Weather Concreting" and in ACI 308-92, "Standard Practice for Curing Concrete," may be used to estimate the rate at which water will evaporate from concrete. Note that the chart relates air temperature, relative humidity, concrete temperature, and wind velocity to arrive at a predicted rate of evaporation from the concrete surface.

ACI recommends that if the predicted evaporation rate exceeds 0.2 pounds of water per square foot per hour (1 kilogram of water per square meter per hour), then preventative measures ought to be initiated. For silica-fume concrete, preventative measures are usually required when the predicted rate of evaporation reaches about one-half of the rate for conventional concrete.

The predictions from the chart are only as good as the data that is supplied. Calling a weather station miles form the project site may supply general information, but it is the conditions on the placement site that are critical.