Influence of Aggregate Structure on Mode-III Interfacial Fracture between Concrete and CFRP

One of the crucial issues in the use of fiber reinforced polymers for civil engineering applications is the interfacial bonding between the different materials used. As a load transfer from the concrete to the composite components occurs via shear stresses in the interfacial region, studies of the interfacial bond quality should concentrate on load situations in which primarily shear stresses are induced. In this study, a 3-Point Bending Test was modified to initiate shear failure under Mode-III conditions in the interface between a composite and a concrete component. In particular it was the objective to study the interfacial shear strength between three different concretes and an unidirectional carbon fiber reinforced epoxy matrix system. The three concretes had the same compressive strength (B35 KP, German Standard), but differed in the type of filler material: (a) “heavy” concrete, filled with granite (Diorit) particles, (b) “normal” concrete, filled with gravel grains (Pyrite), and (c) “light weight” concrete, filled with vopourtone (Liapur). The mechanical test results showed that both the type of filler exposed to the joint surface as well as the type of adhesive used clearly influence the interfacial shear strength. Best values were achieved with Diorit-fillers, and the Sikadur-adhesive was in all cases superior to the Dywipox-adhesive. Reasons for these differences were demonstrated by light optical and scanning electron micrographs of the fractured surfaces.