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Why is liquid nitrogen added to fresh concrete sometimes instead of ice block/chilled water?

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Traditionally, chilled water and ice have been employed to reduce the temperature of concrete mix in hot weather condition. Chilled water has a limitation in its cooling potential. For instance, even if all mixing water has been converted into chilled water, the temperature reduction achieved in concrete mix is only about 2.7oC.

The complete/partial replacement of mixing water with ice may be a better alternative in terms of cooling potential because ice possesses power from heat of fusion. However, it presents practical difficulty in ensuring homogeneous distribution of ice within concrete mix and the complete melting of ice. Unmelted ice block may be hidden in concrete mix and if it melts before concrete setting it creates high water cement ratio locally. In case unmelted ice block melts after concrete hardening, large voids would be formed which impairs the concrete strength and durability.

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Liquid nitrogen is supercooled and has a very high cooling potential. Fresh concrete can be cooled inside a read-mix truck by injection of liquid nitrogen. Liquid nitrogen is kept at a temperature of -196oC in storage tank. Once liquid nitrogen is added to fresh concrete mix, nitrogen in liquid form changes to gaseous state under normal atmospheric pressure in a very short time (e.g. milliseconds).

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.

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  • rupesh October 20, 2010 at 11:50 pm

    thanking you sir

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