Experimental Investigation On The Influence Of Coarse Aggregate For Mortar Crack Propagation

On the meso-scale, concrete is generally considered as consist of mortar, aggregate and interfacial transition zone between them, the mechanical behavior of composite is influenced by the characteristics of the three-phase and the interaction among them. Because of the complex properties of mortar, aggregate and interface, it is more complex for the study of concrete original crack from meso level. As one kind of heterogeneous composite material, concrete crack propagation depends on the material properties and stress condition. Concrete material property which can influence the crack propagation path includes relative strength of mortar and coarse aggregate, the strength of mortar and aggregate interface, etc. Therefore, to better understand the influence of coarse aggregate to concrete, mortar crack propagation, the following research work has been carried out:(1) Experimental study on tensile strength of mortar-rock interfaceThe interface composite specimen made by half mortar and half rock was adopted, which size was 200mm×100mm×100mm. Researches were conducted on direct tensile and splitting tensile strength of mortar-rock interface influenced by different mortar strength, types of rock and the roughness of rock surface. Results indicate, the tensile strength of mortar-rock interface increases with the increase of interfacial roughness, strength level of mortar.(2) Study on the fracture properties of mortar-rock interfaceThree-point bending tests were carried out to investigate the influence of strength level of mortar, type of rock and roughness of rock surface on the fracture properties of interface. The specimens size were 700mm×150mm×40mm, which made by half mortar and half rock. Results show that, peak load and crack initiation stress intensity factor, fracture energy all significantly increase when rock surface is treated. So, bearing capacity of the interface can be improved with the increase of rock surface roughness. Types of rock have a significant impact on the interfacial properties, both peak load and fracture energy of sandstone specimens are higher than the granite specimens when other components of three-point-bending specimens are exactly the same.(3) Experimental investigation of three point bending test of coarse aggregate embedded in mortar specimens.Three-point bending specimens were designed with aggregate pre-embedded in mortar, whose size were 700mm×150mm×40mm. Through changing the strength level of mortar, type of rock and roughness of rock surface, different crack propagation paths are realized when crack tip encounters aggregate:crack crosses through the coarse aggregate, crack propagates along the interface. Experimental results reveal that, the nature of interface transition zone is improved when silica fume is added, the strength of mortar plays an important role in crack propagation path, crack propagate through the coarse aggregate of all high strength mortar specimens. Crack initiation stress intensity factor of all specimens are less than the fracture toughness of equivalent strength mortar, this phenomenon shows that, crack resistance is weakened when coarse aggregate is added into mortar. When crack propagates along the interface, coarse aggregate is withdrawn from mortar by tensile stress. Since the bond between aggregate and mortar, crack can continue to transfer stress, thus, the brittle fracture of mortar is improved.