Microcracking and Permeability of Concrete to Liquid Nitrogen
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compressive strength; concretes; cryogenics; liquefied gases; liquidnitrogen; microcracking; modulus of elasticity; permeability; storage tanks;tensile strength; thermal properties.
Liquefied natural gas (LNG) storage tanks are often constructed with alloy steel liners as the primary containers, and concrete outer tanks as secondary containers. Substantial cost saving and enhanced safety could be achieved by employing prestressed concrete in both capacities. For concrete to serve in primary capacity, low permeability has to be demonstrated. Results are presented from a preliminary investigation into the factors affecting concrete permeability to liquid nitrogen [ - 196 C (-321F)]. The results show that the type of aggregate and factors related to aggregate-cement paste interaction play a major role in the process. Permeability coefficients as low as 5 x 10-l9 m2 ( 8 x 10-16 in.2) were obtained. Microcracks observed in tested specimens are thought to result from incompatibilities of the physical and thermal properties between the aggregate and the cement paste. Crack width is probably the primary parameter affecting permeability. The results point to lightweight rounded aggregate as a potentially suitable low permeability concrete-making material.