How to Guide: Hot Weather Concreting

The summer months are fast approaching and, unfortunately, hot weather can create problems in the mixing, placing, and curing of concrete. In terms of concreting, hot weather is defined as any period of high temperature in which special precautions need to be taken to ensure proper handling, placing, finishing and curing of concrete.

Why are we taking special precautions in consideration of hot weather in relation to concrete? For several reasons. It is important that hot weather be taken into account when planning concrete projects due to the potential effects on fresh and recently placed concrete. High temperatures alone can cause increased water demand, accelerated slump loss, and can have a major effect on set time.

The high temperatures associated with hot weather, as well as high wind velocity and low humidity, can affect fresh concrete in two important ways:

• The high rate of evaporation may induce early plastic shrinkage cracks or drying shrinkage cracks
• The high evaporation rate can remove surface water necessary for hydration unless proper curing methods are employed

Fortunately, because we know the factors and risks associated with hot weather concreting, there are steps we can take to prevent and minimize the adverse effects.

Follow These Rules for Hot Weather Concrete Placement:

• Modify concrete mix designs as appropriate
• Introduce the use of set time retarders such as Delvo
• Moderate the heat of hydration by reducing cement content with the use of pozzolans (fly ash)
• Incorporate chilled water or ice as part of the mixing water
• Have adequate personnel to quickly place, finish and cure concrete
• Limit the addition of water at the job site (only add water on arrival at the job site to adjust the slump)
• Dampen the subgrade, as well as forms and reinforcement, prior to the concrete placement
• Do not allow excessive water to pond.
• Begin final finish as soon as the water sheen has left the surface
• Start curing as soon as finishing is complete and continue the curing for at least 3 days
• Cover the concrete with wet burlap and plastic sheeting or use a liquid membrane curing compound to prevent evaporation
• If low humidity and high winds are predicted, an evaporation retardant is suggested to avoid plastic shrinkage cracking in slabs

Weather factors are huge considerations to make when pouring concrete. Maintaining an appropriate level of moisture in the concrete is the highest priority. “Hot weather” concreting can be difficult because of a combination of factors. High temperatures, low humidity and high wind speeds can increase the rate of evaporation and make it more challenging to retain moisture in the concrete. It’s important to consider this combination of factors and take the previously mentioned rules for hot weather concreting into account when placing concrete.

Are you planning a project that includes a hot weather concrete pour? Do you have more questions on the process? How can we help? Contact us today! (916) 851-8300