Environmental factors, particularly hot weather conditions, affect concrete properties and the construction operations of mixing, transporting, and placing of the concrete materials.
By understanding how these factors—heat, humidity, and even wind—affect the curing of concrete, producers can adjust mix designs and compensate in a variety of other ways to maintain high-quality standards and avoid issues with the finished product.
What is Hot Weather Concreting?
The ACI defines hot weather concreting as: “One or a combination of the following conditions that tends 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.”
The calendar doesn’t always decide when it’s “hot weather”—climatic conditions of high winds, low relative humidity, and solar radiation can occur any time, especially in warmer climates. Not only that, failure to manage these conditions can make your pours challenging—and expensive. Read on for five ways that hot weather can impact your profit, and what you can do to work around it to maintain profitability.
The problem: Increased water demand
The impact on your profits: Additional water costs, both in supply and trucking
The solution: Fly ash, slag cement and calcined clay all react more slowly than portland cement and evoke less heat. That means they’re less susceptible to rapid setting, and are also less adversely affected by elevated-temperature curing. CarbonCure injects carbon dioxide (CO2) into fresh concrete while it's being mixed. Once injected, the CO2 chemically converts into a mineral, which permanently eliminates the CO2 and maintains the concrete’s strength. This enables concrete producers to safely reduce the cement content in concrete mix designs— in turn reducing the risk of using more water for a higher-cement mix.
The problem: Increased slump loss
The impact on your profits: Additional water costs, both in supply and trucking
The solution: Engineers sometimes specify lower or higher water/cementitious material (w/cm) ratios than necessary to achieve strength because they’re trying to influence other characteristics, such as durability or cracking. Mixing rock, sand and cement creates voids that must be filled with water. Additional water is necessary to separate the particles or else the concrete will be unworkable. When temps rise, water can evaporate quicker —leading to on-the-go changes and water additions. To reduce the amount of cement, you must first reduce the amount of water. Bring in more SCMs, and CarbonCure—a stackable technology that enables cement reductions while maintaining strength and performance—and you can send out that water truck.
The problem: Accelerated setting time
The impact on your profits: Difficulty to place and finish - so you spend longer on your job with a poor quality finished product
The solution: This is where mix design comes in—ong before you head to the job site. Some fly ashes contain high proportions of aluminates. There’s enough gypsum in the cement to control the aluminates in the cement, but additional aluminates from the fly ash could upset the balance between them. If you have a choice about it, blended cements already have the right amount of gypsum for the combined portland cement and fly ash. Fly ash can also reduce heat of hydration—which can be useful in hotter temperatures—but can be sensitive to curing temperature. It’s important to make sure that fly ash content is properly calculated before pouring.
The problem: Evaporation on the surface of your placed concrete
The impact on your profits: Shrinkage and cracking make clients unhappy - and that’s not what your business needs
The solution: Planning ahead is your best solution. Your designer can play a key role here—by reducing the heat of hydration with the inclusion of more SCMs, the risk of cracking is reduced. Although it seems counterintuitive, don't reduce your water content to an excessively low w/cm—rapid evaporation and high temperatures make this a risky move. Instead, try to pour in the cooler hours of the day, and avoid thermal shock when you remove forms.
The problem: Air content is affected by hot weather
The impact on your profits: Mismanaged air content can negatively affect workability and set times
The solution: When the temperature rises, so will your dosages of air-entraining, water reducing and retarding admixtures. The key is to make sure you know how the dosage will perform in the heat, so test your mix in advance at an elevated temperature. Don’t wait until you arrive at the job site to time workability and set times—all need to increase in hot weather. Another advantage to advanced testing will give you an idea of curing—remember that concrete cured at high temperatures early on will lose later-stage strength.
Pouring in high temperatures doesn’t have to be a problem for your business, so check that weather forecast, conduct advance testing and optimize your cement and admixture content to ensure success. When adopting CarbonCure, CarbonCure’s Technical Services team acts as a full-scale quality control and testing team that supports your internal operations, and will work closely with you to make sure your mix can handle the heat. Learn more at in our webinar, here: https://www.carboncure.com/resources/best-practices-for-hot-weather-concreting/
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