Tech Bulletin No. 6 - Hot-Weather Concrete Practice

Evaporation Rate Nomograph

In case you thought winter would never end—look out, summer is here!

With it comes a change in concrete practice. Temperature, humidity and wind create challenges to proper placement and curing.

The Evaporation Rate Nomograph (shown above) is a tool developed by the NRMCA in 1960 to combat rapid-drying problems such as plastic shrinkage cracking. The example line in light blue shows the steps and variables needed to determining evaporation rate.

When the rate is above about 0.2 lb/ft2/hr, special curing techniques are needed to avoid cracking. These include water fog, plastic sheets, wet burlap, or curing agents.

Curing is to concrete what resting is to a good steak; that final, critical step to perfection. Mmmm-boy!

For more info refer to ACI 308R, ACI 305R, or NRMCA-CIP 5, 11 and 12. Holcim has also developed a mobile app that predicts plastic shrinkage using current weather conditions.

Learn more: aci.org; concreteinternational.com; asu.edu; holcim.us; concrete.org