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Hot Weather Concreting

19 May 2021, Posted by F.A. in Concrete Forms Tips

Construction professionals who work with concrete know that environmental factors can impact concrete properties and the construction operations of mixing, transporting, and placing the concrete materials. One of the factors that heavily impacts this can be hot weather conditions. Understanding how heat, humidity, and even wind can impact the curing of concrete, workers can adjust mix designs and compensate to maintain high-quality standards and avoid issues with finished products. Whether you are starting a new project or researching the best concrete forms for sale, understanding the way hot weather concreting works can be important.

What Is Hot Weather Concreting?

Hot weather concreting is defined as “one or a combination of the following conditions that ends to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration, or otherwise causing detrimental results: high ambient temperature, high concrete temperature, low relative humidity, and high wind speed.

In most places, hot weather problems are primarily a factor in the summer. However, climatic conditions of high winds, low relative humidity, and solar radiation can occur year-round, especially in warmer climates. As such, hot weather concreting is any period of high temperature in which precautions need to be taken to ensure proper handling, placing, finishing, and curing of concrete.

There is no set exact temperature where special precautions become necessary, though some experts say 80 F (27 C) is a good benchmark to use. This is generally the temperature that starts to impact the efficiency of the cementitious system. A better indicator of hot weather conditions for concrete is the evaporation rate.

Problems in Hot Weather Concrete

When conditions do qualify a project as hot weather concreting, a range of problems can occur. Mixing, placing, and curing hydraulic cement concrete can adversely affect the properties and serviceability of the concrete. When precautions are not implemented efficiently during hot weather, the concrete could be damaged by plastic shrinkage cracking, thermal cracking, and decreased 28-day strengths.

In a freshly mixed state, problems encountered in hot weather may include:

• Increased water demand, reducing the water-cementitious ratio
• Increased slump loss leading to a need for added water at the job site
• Accelerated setting time, which can create issues with handling, compacting, and finishing, as well as a greater risk of cold joints
• Increased potential for plastic shrinkage and thermal cracking, due to the evaporation of water on the surface of the placement
• Difficulty controlling air content- depending on the cementitious system and admixture package, a gel may form and cause air bubbles to break, decreasing the air content
• Need for the concrete to be promptly cured and cut early, which will not be as strong at a later age

Once the concrete is hardened, problems caused by hot weather can never be fully reversed. Deficiencies in hardened concrete may include:

• Increased potential for drying shrinkage and differential thermal cracking due to either cooling of the overall structure, or from temperature differentials within the cross-section of the slab
• Decreased compressive strength resulting from higher water demand
• Increased potential for cold joints, color differences, or other variations in surface appearance
• Decreased water-tightness and durability due to cracking

Minimizing the Impact of Hot Weather

The key to success in hot weather concreting is the planning, for both internal processes at the plant and external processes at the job site.

Teams should be adequately trained to handle concrete in the conditions they are working in, including hot weather. If your team is unaware of the different hydration control admixtures or the effects of the admixtures in hot weather, you can work with your admixture supplier and cement supplier to understand best practices for your specific mix scenario.

A collaborative approach to hot weather concreting is recommended. Meetings with contractors and end customers can make everyone aware of the risks, including the potential for plastic shrinkage and others. This can help to set expectations before other problems occur down the line.

Best Practices for Hot Weather Concreting

On a job site, limiting travel time and using retarding agents are recommended. Prompt discharge with a dampened discharge area and shade and wind breaks is also useful. Protecting cylinders and curing ASAP are best practices. Here are some modern concrete materials you should think to use in order to improve the quality and make the structure more durable.

At the plant, aggregates should be dampened and temperature monitored. Ice can be used for mix water in very warm climates, and a liquid nitrogen cooling system may be a worthy investment. Keep in mind that specialty mixes may require additional precautions.

When you are searching for concrete forms and concrete formwork ties for sale to be used in a hot weather scenario, contact an expert at Forming America to get started.