Journal of Cold Regions Engineering

The behavior of precast concrete beams prestressed using carbon fiber-reinforced polymer (CFRP) rods was studied under the combined effects of sustained load and low temperature. Three 13-year-old concrete T-beams were tested, including two with CFRP rods stressed to different levels and one with steel prestressing strands. Test beams were exposed to $-27°\mathrm{C}$ while being subjected to a sustained load of 25% of their flexural strength for 163 days. The sustained load was equivalent to the service load level and produced cracking in two of the beams with the lower prestress levels. Results were then compared to those obtained from a set of similar beams subjected to the same sustained load at room temperature. Deflection increase under sustained load at low temperature was generally small and similar to that at room temperature. Prestressing strain decreased as the temperature decreased in the CFRP-prestressed beams. Exposure to low temperature likely contributed to a 19% reduction in strength and a change in failure mode from flexure to bond failure.

A firn air cooling system that utilized the natural reservoir of cool air at depth in polar ice sheets was tested at Summit Station, Greenland during the summer of 2010. Cooling is required on station to meet the requirements for food safety and scientific core storage. Firn air cooling is a potential replacement for traditional mechanical cooling systems. The system design, installation, and results of several experiments are presented. The system cooled a $27{\mathrm{m}}^3$ enclosed, insulated structure from $-20$ to $-25°\mathrm{C}$ using a 10-m borehole and a fan pumping the naturally cool air. The system was easy to install in a short time frame and was low cost from an equipment and operating perspective.

This study formulates a heat flux boundary model to assess cold region ground temperatures and to distinguish the difference between this boundary type and a temperature boundary type. This formulation considers the impacts of the ground-surface albedo and of the environmental conditions (e.g., air temperature, wind speed, and solar radiation) on the ground-surface heat flux and subsequent subsurface temperature profiles. The predicted results are verified by the observed temperature profiles at a test station on the Qinghai-Tibet Plateau. A temperature boundary model is also used to simulate the ground temperature and is compared to the same field-observed temperature profiles. The paper speculates whether neglecting the evaporation-induced heat flux in the formulation of the heat flux boundary model compromises the ground temperature profile calculation. The effect of the evolution of the surface albedo on the redistribution of the ground temperature profiles is also discussed.

The effects of freeze-thaw cycles and seawater corrosion on the material properties of air-entrained concrete specimens and structural behavior of reinforced air-entrained concrete beams under persistent loads were investigated in the laboratory. The air content of the specimens was designed to be 3.2 and 6.1%. Results show that when subjected to alternating actions of freeze-thaw cycles and seawater immersion, the compressive strength of concrete decreased when the number of freeze-thaw cycles increased, with the ones with higher air content showing better resistance to freeze-thaw attack. In the case of reinforced air-entrained concrete beam, the presence of persistent loads accelerated the structural behavior deterioration process. When the persistent load reached half of the ultimate load, the reduction of the ultimate load and ductility was found to be a couple of times greater than those without the persistent load. Compared to the beams with 3.2% air content, the yield load, the ultimate load, and the ductility of the beams with 6.1% air content increased by 0.5, 2.5, and 13.2%, respectively. It was concluded that air entrainment has a more considerable effect on enhancing the ductility of reinforced concrete structures in cold coastal regions.