Improved mechanical properties of CFRP laminates at elevated temperatures and freeze-thaw cycling

摘要

Externally bonded Fiber Reinforced Polymer (FRP) laminates are recognized as an effective system to repair or strengthen existing structures in the field of buildings. Despite the evident advantages of FRPs over traditional materials, the greatest impediment to worldwide utilization is represented by the limited knowledge of composites behavior at elevated temperature and/or freeze-thaw cycling exposure. In order to investigate this aspect, a series of mechanical tests have been carried out on innovative epoxy based-matrices and on carbon FRP coupons exposed to different temperature and humidity conditions in an environmental chamber. Since commercially available resins exhibit a reduced capacity to transfer loads over fibers around glass transition temperature (T_g) which, for cold-cured systems (i.e. systems cured around the ambient temperature), is somewhat comparable to the operating temperature, the innovative matrices have been formulated with the aim to attain T_g values significantly higher than those exhibited by presently used epoxy based-systems. The strategy adopted for the formulation of such resins is based on the key idea that for cold-cured epoxy resin, it is essential to increase the exothermal cross-linking reaction heat allowing the curing reaction in the bulk of the material to be carried out at temperatures higher than ambient temperature. The results of Differential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA) and Thermo-Gravimetric Analysis (TGA) as well as results of tension tests on FRP laminates subjected to severe operating conditions are presented and widely discussed in this paper. The experimental results pointed out that the innovative epoxy-based formulations provide significant improvements on the mechanical properties of FRP laminates exposed to elevated temperatures or to freeze-thaw cycles.