Constitutive modelling and investigation of bond-slip relationship in concrete for direct liquefied natural gas containment
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This proposal follows up on the recently completed NPRP Cycle 4 project (4-410-2-156), which investigated thermal dilation and internal damage of cryogenic concrete utilized for direct liquefied natural gas (LNG) containment. In the recently completed project, we demonstrated through different tests that a concrete can be produced that does not develop significant damage during cooling to cryogenic temperatures. We also developed an experimentally validated model that allows us to predict thermal contraction of the concrete as a function of mixture design and cooling rate, which will allow optimized mixture design and filling procedures to reduce stresses. From the foregoing, it is obvious that replacing 9% Ni steel with concrete in primary LNG containment tanks is a promising technology that would lead to at least 10 â 15% cost savings. However, there are missing gaps that need to be addressed in the current proposal. First, there is a dearth of information on constitutive modelling of concrete under cryogenic conditions. Hence, the LNG storage industry is risk averse on utilizing concrete for direct LNG containment as there is no clarity on the behavior of the concrete-steel interface under cryogenic conditions. Therefore, this work will develop constitutive models to provide clarity on the interaction (bond slip) of steel with concrete under cryogenic conditions. The models would in turn enable the prediction of cracking or damage of cryogenic concrete. Moreover, such models are important and applicable whether concrete is used for direct LNG containment or for the conventional secondary concrete containment. Second, this work will study the thermal properties of concrete such as thermal conductivity and specific heat capacity at cryogenic temperatures as inputs into the constitutive models. Especially, as information on the thermal properties are necessary to predict stress development during cryogenic cooling. Further, the bond slip relationship between steel and concrete will be experimentally investigated for an improved knowledge of the parameters controlling the interaction between steel and concrete under cryogenic conditions. This would involve investigation of fracture and damage behavior of cryogenic concrete.