Nondestructive and Laboratory Evaluation of Damage Gradients in Concrete Structure Exposed to Cryogenic Temperatures

This paper discusses the use of pulse velocity, dynamic Young’s modulus of elasticity, and air permeability of concrete to evaluate the extent of damage and damage gradients to a concrete structure exposed to thermal shock and subsequent cryogenic temperatures. Liquefied natural gas (LNG) is maintained in liquid form at cryogenic temperatures typically below $-160°\mathrm{C}$ $(-260°\mathrm{F})$ . The elevated concrete pedestal and precast concrete piles supporting a LNG storage tank were exposed to cryogenic temperatures following a leak of the LNG. The engineering assessment of the concrete structure consisted of a nondestructive evaluation phase using ultrasonic pulse velocity and a subsequent laboratory phase based on concrete cores. Dynamic Young’s modulus of elasticity and air permeability index of $25\mathrm{mm}$ $\left(1\mathrm{in.}\right)$ thick disks sawed from the cores were determined. Analyzing concrete disks at $25\mathrm{mm}$ $\left(1\mathrm{in.}\right)$ increments permitted assessment of changes in these properties with depth and enabled evaluation of depth of damage and damage gradients. The laboratory study confirmed that the distressed zone was limited to a near-surface area of concrete as suggested by the results of pulse velocity testing.