Long-Term Performance of External Bonding Under Moisture and Temperature Effects

There have been many cases of quickly deteriorated interfaces for external bonding with FRP and/or cementitious materials in actual structures. It seems that we have not known proper design method nor detailing for long-term durability after being strengthened by external bonding. There are many factors for durability of the interface. This paper presents the results of recent studies on interface bonding property under effects of moisture and temperature, which are both single effect and combined effects, in the cases of both external bonded FRP and cementitious materials. The testing conditions include (1) wet condition for 18 months, (2) wet and dry cycles for one and half month, (3) combined wet/dry and temperature (both cases above and below freezing points) cycles, etc. There have been clear effects of both moisture and temperature on the interface bonding properties due to sensitivity of resin property. Generally, the effects of temperature are greater than those of moisture. The great combined effects of moisture and temperature were found under freeze thaw cycles under full immersion. The effects of moisture and temperature are less significant in case of rougher surface of substrate concrete. At the end of paper the design method for long-term durability of concrete structure strengthened by external bonding with FRP or cementitious materials is briefly discussed. And the current code drafting activities on external bonding in fib and Japan are introduced.