Non-destructive evaluation of concrete mixtures for direct LNG containment

• Six concrete mixtures are evaluated for damage resistance during cryogenic cooling.
• Strong correlation existed between acoustic energy emissions and porosity changes.
• Damage detected in the concretes was in the form of microcracks < 22 microns.
• Durability of trap rock aggregate concrete for primary LNG storage tanks is shown.

The suitability of six concrete mixtures for use in direct containment of liquefied natural gas (LNG) was assessed using nuclear magnetic resonance (NMR), X-ray computed tomography (XRCT) and acoustic emission (AE). The mixtures were prepared with river sand as fine aggregate using different coarse aggregates. The mixtures were cooled from ambient to cryogenic temperatures at a cooling rate of 3 °C/min. Proton NMR measurements and XRCT imaging were carried out before and after cooling to monitor changes in porosity and pore size distribution, and internal microstructure, respectively. AE sensors monitored damage evolution during cooling and warming. NMR results indicated porosity increases of 0%, 0.3%, 1.4% and 3.3% in the non-air-entrained trap rock aggregate, limestone aggregate, sandstone aggregate and lightweight aggregate concrete mixtures, respectively. The air-entrained trap rock and limestone mixtures showed porosity increases of 0% and 1.9%, respectively. There was a strong positive correlation between AE cumulative energy and NMR porosity change. XRCT imaging generally showed no frost-induced cracking in the concrete mixtures. Thus, pore structure changes and apparent damage were in the form of microcracks less than the XRCT resolution (22 microns). The results highlight the utility of trap rock aggregate in production of durable concrete for direct LNG containment.

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