During the last decades, traffic loads by heavy vehicles have increased due to requirements of the current society and bridges are getting older and this fact has to be considered when the state of existing bridges is evaluated. Many concrete structures, for instance lateral cantilevers of highway box-girder bridges, can be strengthened on the upper side with externally bonded (EB) Carbon Fiber Reinforced Polymer (CFRP) strips in order to increase their load-bearing capacity in flexure. These additional reinforcements can be applied as an unstressed or prestressed system. The main goal of this research project is to analyse the effect of the temperature on the bond between the concrete substrate, the epoxy resin layer, and the externally bonded (prestressed and unstressed) Carbon Fiber Reinforced Polymer strip. A focus is on the special anchorage method for the prestressed CFRP strips, the so-called gradient anchorage.
If CFRP strips and epoxy adhesives are applied on the upper side of bridges, they can reach elevated temperatures due to the sealing process and the subsequent application of the asphalt layer during the construction or afterwards due to the sun heating. In spite of the great number of experimental works carried out concerning the behavior of reinforced concrete elements strengthened with unstressed and prestressed CFRP strips, few experimental investigations have been done up to now regarding the behavior of such elements strengthened with prestressed CFRP strips anchored with the gradient anchorage under elevated temperatures. In the frame of the research project, an experimental campaign is being carried out at Empa in order to assess the short and long-term behavior of prestressed and unstressed CFRP strips glued on concrete under different elevated temperature environments.
Figure - Large-scale test on a RC slab with mastic asphalt strengthened with two prestressed EB CFRP strips