Concrete placement during hot weather can lead to problems if precautions are not taken to control placement temperatures. Such problems include: decreased compressive strengths and durability when fully cured; plastic and thermal cracking; and lack of uniformity in surface appearance. One traditional approach to lowering concrete temperatures is to use ice to supplement a portion of the batch water. However, this at times leads to operating and quality control problems. An alternative to ice for providing necessary cooling is to use liquid nitrogen (LIN), an inert liquid with a temperature of -320 degrees F.
LIN is delivered to the batch plant and is stored on site/used as needed. LIN can be used to cool the batch water, produce an ice-and-water slush mixture, and/or cool the cement. When LIN comes in contact with another material such as batch water, it cools the material rapidly, evaporates, and simply returns back into the air. For cooling cement, LIN is used as the cement is off-loaded from the bulk transport to the storage silo. With this system the LIN flow is activated when the cement starts flowing. The mixing action created by the LIN injection ensures efficient, uniform cooling, which is capable of reducing cement temperatures by as much as 45 degrees, with concrete temperature reductions of as much as 5 degrees F.
If greater temperature reductions are required, all three systems (cooling batch water, producing ice-and-water slush mixture, and cooling the cement) could be used together to reduce the concrete temperature by as much as 23 degrees F. For many projects, LIN cooling can prove to be more economical than ice cooling, as the operating cost is based mostly on nitrogen used. With ice, operating costs include the cost of ice, labor for handling ice, and maintenance of the ice handling equipment. Many concrete producers have selected liquid nitrogen systems to obtain better quality control, improved operation, and overall reduction in project costs.