External prestressing of existing reinforced concrete (RC) beams by means of bonded fiber reinforced polymer (FRP) strips is getting more and more common as a possible strengthening technique for either underdesigned or damaged members. However, the current technical solutions for external prestressing with FRP require a mechanical anchorage system at the end of the strip, in order to react to the high interface stresses arising in that part of the FRP-to-concrete interface. An alternative solution based on a gradual reduction of the prestressing force in the end zone of the FRP strip which avoids any mechanical anchorages has been recently developed at Empa. Generally speaking, this solution, called “gradient method”, works on the accelerated curing of epoxy resins under heating exposure. Therefore, a better understanding of accelerated curing of adhesive by heating is necessary. The present paper describes some experimental results of pull-off tests carried out on FRP strips glued on concrete blocks and cured through heating with variable duration. The maximum force at debonding onset observed in the tests on specimens with different curing durations at elevated emperatures were compared with a reference test carried out on a specimen fully cured at room temperature for three days. Furthermore, the displacements measured by means of an optical image correlation system are presented with the aim of showing the effect of the heating duration. Moreover, a simple calibration procedure has been used for identifying the supposed bi-linear shear-stress-slip relationship describing the effect of partly cured adhesive on the behavior of the FRP-to-concrete adhesive interface.
Effect of partly cured adhesives on bond-slip relation ship of FRP-concrete interface
MARTINELLI, Enzo;
2011-01-01
Abstract
External prestressing of existing reinforced concrete (RC) beams by means of bonded fiber reinforced polymer (FRP) strips is getting more and more common as a possible strengthening technique for either underdesigned or damaged members. However, the current technical solutions for external prestressing with FRP require a mechanical anchorage system at the end of the strip, in order to react to the high interface stresses arising in that part of the FRP-to-concrete interface. An alternative solution based on a gradual reduction of the prestressing force in the end zone of the FRP strip which avoids any mechanical anchorages has been recently developed at Empa. Generally speaking, this solution, called “gradient method”, works on the accelerated curing of epoxy resins under heating exposure. Therefore, a better understanding of accelerated curing of adhesive by heating is necessary. The present paper describes some experimental results of pull-off tests carried out on FRP strips glued on concrete blocks and cured through heating with variable duration. The maximum force at debonding onset observed in the tests on specimens with different curing durations at elevated emperatures were compared with a reference test carried out on a specimen fully cured at room temperature for three days. Furthermore, the displacements measured by means of an optical image correlation system are presented with the aim of showing the effect of the heating duration. Moreover, a simple calibration procedure has been used for identifying the supposed bi-linear shear-stress-slip relationship describing the effect of partly cured adhesive on the behavior of the FRP-to-concrete adhesive interface.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
