Concrete is the most widely used man-made material on earth. From unparalleled strength and durability to high energy efficiency, there are various benefits of concrete. High temperatures can, however, significantly impact the quality of concrete.
Hot Weather Concreting Defined
Hot weather concreting is defined as one or a combination of the below conditions:
- High concrete and ambient temperature (77-95°F)
- Low relative humidity
- High wind speed
These conditions can impair the quality of concrete by accelerating moisture loss and cement hydration rate.
Challenges of Hot Weather Concreting
Here are some effects of hot weather on concrete:
Increased Water Demand
When temperatures soar, concrete starts losing moisture at a rapid pace. When this happens, more water is required for maintaining the workability of concrete. It is also essential to maintain the water-cement ratio. Failure to do so will negatively impact the strength and durability of concrete.
Decrease in Setting Time
When the rate of hydration reaction rises rapidly, both the initial setting time of concrete and the time available for transit, placing, and finishing decrease.
Loss of Long-term Strength and Durability
An increase in the rate of hydration reaction negatively impacts the long-term strength of concrete. Adding water to concrete to make up for moisture loss can do more harm than good. When concrete absorbs moisture, small pores start forming. These pores can impact its durability.
Thermal and Plastic Cracking
The rate of evaporation increases with an increase in temperature and wind speed. When water moves from the inner surface of concrete, moisture dries up faster than the rate of replacement. This leads to the development of plastic shrinkage cracks on the surface of concrete.
Maximum Allowable Concrete Temperature and Relative Humidity During Concrete Placement
- If the temperature is 90°F the relative humidity should exceed 60 percent.
- If the temperature is 85°F, the relative humidity should be between 40-60 percent.
- If the temperature is 80°F, the relative humidity should be less than 40 percent.
Tips for Hot Weather Concreting
- Keep aggregates and mixing water as cool as possible. When the temperature soars, replace a portion of water with ice.
- Use evaporation retardants.
- Create effective communication between the job site and the ready-mix plant. This will help reduce transit, placing, and finishing time.
- Place the concrete early morning or late afternoon when the temperature is low.
- Cure only when you are sure that the surface is hard enough to resist marring.
- Take steps to minimize the time gap between the start of mixing and placement.
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