SIZE EFFECT AND INFLUENCE OF AGGREGATE ROUGHNESS IN INTERFACE FRACTURE OF CONCRETE COMPOSITES

The effect exhibited by interface fracture and the influence of aggreg ate roughness on mortar-aggregate interface fracture parameters are in vestigated The concrete composites studied are bi-material systems con sisting of a granite inclusion embedded in high-strength mortal: Newly developed compact sandwiched beam specimens of three different shes a re tested in pure Mode I and in mixed mode (opening and shear) loading conditions. Three different roughnesses of the aggregate inclusion ar e used: smooth, sandblasted, and flamed. The critical interface fractu re energy release rates and corresponding size effect parameters are c alculated from the fracture loads of the composites. The size effect d ata are correlated to an existing sire effect law; strong size effects are observed, indicating the brittle nature of interfaces in cementit ious materials. Parametric analysis shows that for a given loading con dition the critical interface fracture energy release rate increases w ith rougher aggregate surfaces for both Mode I and mixed mode traction s. Similarly, for a given aggregate rough ness the interface fracture energy release rate is also shown to increase with greater shear loadi ng.