Cold Weather Concreting
According to the American Concrete Institute (ACI 306R-16):
“The conditions of cold weather concreting exist when the air temperature has fallen to, or is expected to fall below, 40°F (4°C) during the protection period. The protection period is defined as the amount of time recommended to prevent concrete from being adversely affected by exposure to cold weather during construction.”
In other words, concrete needs to be protected from the adverse effects of being exposed to cold temperatures for it to cure properly. When placing concrete in the cold, special precautions may need to be taken. Insulating blankets, heating mats and heated enclosures are typically used to protect concrete from damage due to low temperatures. Without these protection measures, cement hydration can be slowed, or even stopped, and drastic fluctuations in finishing and curing times may occur. If concrete freezes at an early age, it may experience permanent damage.
Modifying the mix design is a good option that can be used in cold conditions. Higher strength mixes, low water/cement ratio mixes, and/or accelerating admixtures are all tools that should be considered when placing concrete in cold weather. Another tool that should be used in these conditions to ensure you meet specifications is temperature monitoring.
Implementing a tool to measure the temperature of concrete is central to any cold weather concrete operation. Knowing the temperature of in-place concrete can be just as critical as mix design, and reliance on ambient temperature data is highly unreliable. A tool that can reliably provide temperature and maturity data can inform decision making. Access to this data in real-time eliminates the guess-work about concrete temperatures and concrete strength (or maturity). This translates into efficiency, cost savings, and confidence in your projects.
There are two categories of technology available for knowing concrete temperatures; recorders and monitors. Temperature recorders may be wired or wireless sensors that are placed in concrete and require someone to visit the sensors in order to access temperature data. These devices typically have a range of 0-25 feet and do not provide the real-time stream of data needed to improve efficiency. Temperature monitors create value on jobsites by streaming real-time data through the cloud. Monitors allow for project oversight in a way that leads to increases in job site safety, efficiency, and cost savings.
The NEX™ system, by Con-Cure®, is a monitoring device that leverages reliable 4G LTE networks to provide real-time temperature and maturity data. There is no need to visit sensors to collect data, as NEX™ automatically streams all information to the cloud. NEX™ also sends mobile alerts when critical maturity points have been reached- keeping you informed. Access concrete temperature data from anywhere, at any time, with NEX™ monitoring by Con-Cure®.
Hot Weather Concreting
Hot weather can affect concrete durability. Some mixes can tolerate heat better than others. With concrete maturity testing, one can monitor the performance of concrete cured at high temperatures to ensure sufficient strength. For example, some high-early strength mixes cure very well at high temperatures (sometimes as high as 170°F!).
Hot weather concreting is defined by ACI 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.”
Various adverse effects on the properties and serviceability of concrete are brought on by hot weather. Just one of those is the effect on strength—concrete mixed, placed, and cured at elevated temperatures normally develops higher early strengths than concrete produced and cured at lower temperatures. There can also be issues with mixing, transporting, placing and curing. Plastic, drying and thermal cracking is also possible.
Curing the initial lab cylinders at high temperature (as tracked by the concrete maturity meter) will give a clear picture of the actual performance under high temperature field conditions, and can identify problems before the job starts.