Wet Lay-Up Manufactured FRP’s for Concrete and Masonry Repair. Influence of Water on the Properties of Composites and of Their Epoxy Components

The assessment of durability of fiber-reinforced polymers (FRP), used to strengthen masonry or concrete structures, if subjected to weathering is a knotty problem. Environmental factors can have a significant effect on their performance in service. In order to investigate on this aspect, the mechanical behavior of two commercial composites, reinforced with unidirectional carbon and glass fibers, respectively, was analyzed after a long term immersion in distilled water. For comparison purposes, three different commercial epoxy resins, used as primer, putty or adhesive to manufacture and apply the composites through the wet lay-up technique to the surfaces to strengthen, were subjected to the same treatment. In order to take into account the peculiarities of the three cold-curing epoxy resins, a novel procedure to dry the specimens before the immersion treatment was used. The mechanical tests, performed on the composites before and after their immersion in water, evidenced that this agent has a limited effect only on the in-plane tensile strength of wet lay-up manufactured GFRP, while the mechanical properties of CFRP are substantially unaffected by water. On the other hand, the effect of water on the thermal and mechanical characteristics of the three epoxy resins is quite severe, with significant reductions in the glass transition temperature, stiffness and strength.