There is often talk of industrial gas growth spurred on by infrastructure development, but a recent first in China is literally an example of gases deployed in groundwork.
China experienced its first successful attempt of using liquid nitrogen to cool a large mass of concrete in the construction of the foundations of the Waisha River Bridge in Shantou, Guangdong, in Southern China in July (2014).
Concrete cooling by liquid nitrogen has been practiced for years in western countries. The heat generated during the curing of concrete can lead to a temperature of 93ºC – if this heat is not quickly neutralised, it can have detrimental effects on the strength of the concrete and can even lead to cracking.
As explained by a researcher at the technical centre of the Second Harbour Engineering Company (SHEC), a subsidiary of the China Communications Construction Company, water with a pipe running in the concrete mass is usually used for concrete coolingneeds in the country. However, the hydration heat generated by such a large mass cannot be easily removed by this traditional method to control the temperature of the concrete at 28ºC, with an ambient temperature of 35ºC.
Use of cryogenic nitrogen was proposed, but this was new to both the engineers and China. There were doubts whether the cryogenic temperature of liquid nitrogen would weaken the properties of the materials, or even cause embrittlement.
Linde GISE, a joint venture of Linde Gas and Guangdong Iron and Steel Group, was contracted for the project and, after some demonstrations to clear any doubts, three liquid nitrogen lances from Germany were brought to the site to cool the concrete during the pouring process. A total of 88520kg of liquid nitrogen was used for pouring and curing; on average, around 10.5kg was used to cool each cubic metre of concrete by 1ºC.
DONG Hanjun, Project Manager of SHEC, said of the results of this first in the country, “Excellent! Better than what we expected! The concrete pouring was originally planned to complete in 72 hours but actually it took only more than 50 hours to finish the whole process, and the required pouring temperature was achieved perfectly.”