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Concrete Cure Control via Cooling |
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Concrete cures by a process known as hydration, where the cement in the concrete mix reacts with water to form a strong bond. Heat is a by-product of the hydration reaction, and the temperatures of curing concrete often reach 200°F.
High curing temperatures can have a detrimental affect on the strength of concrete because the expansion of concrete during the curing process is greater with an increasing temperature. Expansion due to high curing temperatures is a particularly prevalent problem on large pour projects where the inside portion of the pour can be 15-20°F warmer than the exterior portion, which causes the concrete to have less tensile strength or even crack.
Because of this problem, concrete is typically cooled prior to pouring for those projects requiring extra strength, such as underwater bridge seals or power plant projects, or massive amounts of concrete. |
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Concrete can be cooled by various methods, including
- adding ice to the concrete mix
- cooling the aggregate before mixing in an air-conditioned tower (mechanical chilling)
- adding liquid nitrogen to the concrete mix
Liquid nitrogen is an ideal choice that allows convenient cooling, low capital, and maintains the proper water/concrete ratio.
There are four ways to use nitrogen in concrete cooling: chill the batch water, convert chilled water to an ice slush, cool the aggregate before mixing, or spray liquid nitrogen directly into the batch. Direct injection produces the quickest and most dramatic result.
Liquid nitrogen is injected into the back of the cement mixer truck using Linde's injection lance and control system. The precise temperature of the concrete is automatically controlled allowing for a consistent temperature between batches.
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Other cooling methods can present formidable logistics problems on massive pour projects. Liquid nitrogen eliminates those headaches allowing for fast and easy temperature control on simultaneously mixers at the yard.
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