The precast concrete industry, much of which focuses on custom projects and applications, adheres to a strict standard of quality controls for production purposes. These quality controls include paying close attention to the raw materials such as sand, cement, aggregates, chemicals (if needed) and water used in the process and development of the proper mix design. All of the quality control measures taken and all the attention paid to the details and standards set forth by National Precast Concrete Association (NPCA) would be rendered somewhat meaningless if proper curing procedures and techniques were not followed closely.
There is a growing pattern and demand for higher compressive strengths and being able to realize those PSI ratings in a shorter curing cycle time. While these issues can challenge production at any time it is particularly challenging during periods of the year when cold weather becomes a factor. Common problems encountered during the cold-climate times of the year can include but are not necessarily limited to:
- Potential freezing in the early stages of placement
- Inability to achieve required compressive strengths within a specified period of time
- Improper curing procedures
- Frequent and /or rapid temperature change
One of the more critical elements in the curing process is moisture retention. The evaporation rate of this moisture needs to be controlled as well as possible and cold weather is an unacceptable excuse or reason for delaying production. Cycle time can obviously take longer during periods of cold weather and we all know that time is money. In situations where the ambient temperature slows both the evaporation rate and thus the curing time utilizing heat in conjunction with moisture curing has proven to be a successful solution to the problem. I can site an example where the use of electrically powered heating blankets which provided an even distribution of heat also critical to the successful accomplishment of proper cure and compressive strength reduced the cycle time by as much 33 percent.
Two of the most common and conventional means of providing heat in a precast operation during initial cure are steam and hot air. While effective during the “initial” curing stage, neither method is recommended once the concrete slab has attained its “initial” set. The use of an electrically powered heating solution can provide several benefits:
- Freeze protection
- Sustainability of acceptable temperatures to enhance cure
- Accelerate the achievement of specified compressive strength levels while preventing rapid temperature fluctuations during the curing cycle
I encourage you to understanding the factors that impact precast concrete production and general concrete construction in cold-weather and the standards to which you are looking and needing to adhere to.