Insights from bond-slip investigations in different reinforced concrete mixtures for LNG containment

Abstract Understanding the concrete-steel interface's behavior at cryogenic temperatures is important for designing concrete for direct liquefied natural gas (LNG) containment; such behavior is currently unclear. Hence, the work conducted involved pull-out testing in providing insights on the bond-slip relationship and the development of internal strains, which have seldom been measured in cryogenic concrete. Deformed cryogenic steel rebars (16 and 19 mm diameter) were embedded in cylindrical concrete specimens made with either traprock or limestone aggregates, with and without air entrainment (AE). Embedded foil and vibrating wire gages monitored the concrete and rebar's internal strains during cooling and pull-out testing. Pull-out testing involving applied stresses ranging from 34.5 to 241.5 MPa was conducted at normal and cryogenic temperatures. Bond stress was similar in both aggregate types but increased with rebar diameter within the applied stress range. The gages indicated that the rebar and concrete showed similar strain patterns in AE and non-AE traprock, and the AE limestone concretes during cryogenic cooling. However, the rebar gages responded to expansive movements below -20°C in the non-AE limestone concrete. Bond stiffness degradation occurred at higher applied tensile stresses with AE in limestone concrete but at similar tensile stresses in AE and non-AE traprock concrete.