There are many times when concrete projects can’t wait for milder temperatures before beginning construction. For those working with concrete during the cold weather months, proper execution of cold weather concreting is essential. Cold weather concreting takes place when the concrete is placed somewhere that the temperature may fall below 40 degrees F. Certain steps need to be taken to protect against early freezing and thermal cracking. However, low temperature concrete that has been protected from cold weather exposure and properly cured will result in a much durable concrete with a higher ultimate strength. Accelerating admixture and hot water are the recommended combination to allow concrete to set up in a reasonable time, while keeping internal temperatures on track.
The benefits of using hot water:
During cold weather, concrete mixing temperature should be controlled using hot water when necessary so that when the concrete is placed, its temperature is not too low for the conditions and the application. Hot water can be added at the plant during batching. According to the American Concrete Institute (ACI), the more massive the concrete section being poured, the slower it loses heat; therefore, lower minimum placement temperatures are recommended as concrete sections become larger. In a section of 12” or less the minimum recommended concrete temperature is 55 F (13C). For air temperatures above 30 F (-1 C), it is recommended that the concrete temperature be a minimum of 60 F (16 C).
At Folsom Ready Mix we have industrial water heaters that can bring batch water temperatures up to 160 degrees F warming up all of the ingredients in the concrete mix. Concrete at a temperature of 70 degrees F has an approximate set time of 5 hours, half the set time of concrete at 50 degrees F.
Hot water allows for increased concrete temperature, which equals reduced initial set times. This also maintains concrete temperature at or above the recommended placement temperature while reducing the risk of early age freezing.
“Accelerator is added to concrete to speed up hydration (the process by which cement and water react to harden). Depending on temperature, set times can be reduced by several hours, or even cut in half. There are two main points to remember when deciding to work with accelerator: 1) it is the concrete temperature, and not the ambient temperature that dictates the effectiveness of accelerator and 2) accelerator tends to rapidly lose effectiveness under a concrete temp of 50 degrees F. Thus, adding hot water in tandem to accelerator admixture really produces a winning combination that protects concrete […]”
Folsom Ready Mix uses AC 534 as an additive for ready mixed concrete to reduce concrete set times and increase early age strengths. AC 534 is a liquid additive that is ready to use and does not contain calcium chloride and complies with ASTM C 494/C 494 M. AC 534 can be used in a variety of dosages for different temperatures and set times allowing contractors to predict the optimal time of surface finishing and form removal.
Using accelerating admixture allows concrete construction to fast track reducing initial set time and reducing labor costs. It also reduces or eliminates the need for heating and protecting time in cold weather while increasing early strength.
Combining hot water and accelerating admixture:
Concrete needs to gain strength of 500 psi in order to be able to handle the cold on its own. Using hot water and accelerator, we are able to change the mix to set more quickly while protecting the concrete from the cold until it can reach that 500 psi strength.
This combination allows workers to place concrete in freezing temperatures where normally work would be impeded. It also ensures that concrete placed in cold weather reaches required strength for the safe removal of forms in a timely manner. This approach limits rapid temperature changes until the concrete has developed sufficient strength to withstand thermal stresses form cold weather exposure. In contrast, the rapid cooling of concrete and surface freezing or large temperature differences between the exterior and interior temperatures can lead to diminished strength, durability and cracking.
Folsom Ready Mix believes in providing the highest quality concrete to our customer and we do this by providing the best quality products available. Combining Hot Water and AC 534 for concrete placements during cold weather exposure will ensure that your project finishes well and produces a strong and durable concrete.
Are you planning a project that includes a cold weather concrete pour? Do you need a manufacturer you can trust with the process? We can help. Contact us today: (916) 851-8300