Study of the failure properties and tensile strength of rock-mortar interface transition zone using bi-material Brazilian discs

Abstract The interface transition zone (ITZ) between aggregate and mortar of concrete has a weak resistance to static or dynamic loading and failure usually starts from this zone. Therefore, it is essential to study the failure properties and tensile strength of ITZ of concrete under static and dynamic loading. Accordingly in this paper, bi-material specimens of rock-mortar Brazilian Disc were designed. Two types of rock granite and sandstone with smooth and rough surface were selected to prepare the bi-material Brazilian disc (BBD) specimens. Meanwhile, to compare the difference of failure properties with single material, the Brazilian disc (BD) specimen of single granite, sandstone and mortar were also prepared. The static and impact tests were conducted using the BBD and BD specimens, and a split Hopkinson pressure bar (SHPB) device was applied in the impact tests. Because of asymmetry stress distribution in the bi-material Brazilian disk, the tensile strength was determined by an experimental-numerical method. In addition, to simulate the failure process in ITZ, numerical models of the BD and BBD specimens embedded with cohesive elements using Python language were established. The results show that under static loading, the tensile strength of bi-material sandstone-mortar is less than that of both the single sandstone and mortar, while the tensile strength of granite-mortar is slightly lower than that of the mortar but much less than that of the granite. The tensile strength of bi-material with rough rock surface is generally higher than that with smooth rock surface. The dynamic tensile strength is more than 20 times the corresponding static tensile strength, and the dynamic tensile strength increases with loading rates.