Fire-Damage or Freeze-Thaw of Strengthening Concrete Using Ultra High Performance Concrete

Abstract:

There are some reinforced concrete structures exposed to severe environmental conditions might require maintenance or strengthening. Many of these severe circumstances are the result of extreme climate conditions such as low temperature, freeze–thaw action, fire attack, and exposure to deicing salts. Because of this, the environmental durability of both the repair materials and methods used in rehabilitation applications are of utmost importance. A small fire can reach 250°C, while a common blaze can easily produce temperatures of around 800°C. In major conflagrations the temperature can even reach 1100°C. At this level, the heat affects most materials, provoking the spontaneous combustion of some of them and affecting the resistance of others. However, very little research has been performed in evaluating the environmental durability of strengthening materials for concrete members. Very little work has been done on the effects of freeze–thaw cycling on bonding and repair materials. In this study, ultra high performance concrete (UHPC) was used to investigate the effect of strengthening concrete members by fire-damage test or freeze-thaw test. The results show that the mechanical properties of UHPC possess high strength, toughness, and freeze-thaw resistance. The CFRP (carbon fiber reinforced plates) wrapping specimens exposed at 300 °C showed totally failure with the deterioration of the adhesive. The UHPC with bonding 10 mm thickness specimens exposed at 400 °C and duration of 1 hour still in good shape. The UHPC with 1-cm or 2-cm thickness on strengthening concrete members could be obtained specific retrofit effects. The performance of UHPC specimens is better than those of CFRP wrapping specimens during high temperature exposure. The results of slant shear tests show that the bond strength of PC/PC, UHPC/PC and UHPC/UHPC decreased significantly after 600 freeze–thaw cycles or high temperature exposure.