Hot Weather Concreting

With summer in full force, it is important to understand how hot weather conditions affect concrete and how to prevent these adverse effects. Once concrete has been damaged by hot weather, it can never be fully restored.

What is considered "hot weather" in regards to concreting? According to ACI 305, "Hot Weather Concreting," hot weather is any combination of the following weather conditions: high ambient temperature, low relative humidity, solar radiation and/or wind.

Common problems/concerns that arise during these conditions include:

• Increased water demand
• Accelerated slump loss
• Placing and finishing difficulties resulting from accelerated set times
• Rapid drying causing increase in plastic shrinkage cracking
• Long term strength loss
• Potential for thermal cracking in massive structures

Precautionary measures can be taken to alleviate these effects:

• Moisten subgrades and forms so water wont be absorbed from the mix
• Prior to placing, cool aggregates and mixing water to reduce initial temperatures. Use sunshades, windbreaks and temporary covers, such as moistened burlap, over the surface to keep surface temperature down and hold in moisture. Consider fogging to preserve humid conditions.
• To retain moisture, make finishing easier, minimize shrinkage cracking and reduce water demand, use an evaporation retardant such as US SPEC Monofilom ER
• Cure concrete surfaces with US SPEC Maxcure Resin Clear or Maxcure Wax White when surfaces are hard enough to resist marring.
• Seal with a good quality sealer, such as Roca Seal or BRS-25, when concrete is fully cured.