Study On The Effect Of Interfacial Transition Zone Modification On Fracture Property Of Concrete

From the microscopic level,concrete is composed of aggregate,mortar and the Interfacial Transition Zone(ITZ)between them.Compared with mortar matrix,ITZ usually has higher porosity,higher water-cement ratio and permeability,and lower strength,toughness and elastic modulus.Its mechanical properties often have a great influence on the macroscopic fracture characteristics of concrete,and to a certain extent,determine the failure mode of concrete under load.Therefore,it is very necessary to study the fracture characteristics of concrete based on the experimental study of ITZ modification.The granite-mortar composite specimens were designed in this paper,and the effects of the water-cement ratio of mortar,the roughness of bonding surface and the content of silica fume in interfacial agent on the ITZ splitting tensile strength and fracture energy were studied by experiment.Then,the empirical relations between the mechanical properties of ITZ and three modification factors under the relevant modification schemes are put forward.Finally,the influence of related modification schemes on the fracture properties of concrete was studied by numerical simulation.The main work and innovative achievements of this paper are as follows.(1)The granite-mortar hybrid cube specimens were designed to study the tensile fracture property of the ITZ between granite and mortar through the splitting tests.The splitting tensile strength ratio between the hybrid specimens and the pure mortar specimens with the same water-cement ratio was proposed to characterize the weakness of ITZ.The effects of the water-cement ratio of mortar,the roughness of bonding surface and the content of silica fume in interfacial agent on the splitting tensile strength and its ratio were studied,and their relationships were also fitted from the experimental data.At the same time,the bonding mechanism of ITZ was analyzed from the failure characteristics of the fracture(2)The three-point bending tests were performed on the granite-mortar hybrid beam specimens with precast incision.Their curves of load versus crack mouth opening displacement were obtained to calculate the ITZ fracture energy.The peak load ratio and the fracture energy ratio between the hybrid specimen and the mortar specimen with the same water-cement ratio in mortar were introduced to characterize the weak ITZ fracture properties.The effects of the water-cement ratio in mortar,interface roughness and silica fume content in interfacial agent on the peak load and fracture energy were investigated and their relations were also fitted approximately.(3)Using the improved random aggregate generation and distribution algorithm,a2 D meso-heterogeneous numerical model of concrete containing coarse aggregate,mortar matrix and ITZ was established.The three-point bending fracture experiment of concrete beams with precast cut were carried out to verify the accuracy of the model and material parameters selection.The influences of the water-cement ratio of mortar,the roughness of the bonding surface and the silica fume content in the interfacial agent on the tensile fracture properties of concrete were studied,and a quantitative relationship between the tensile fracture behavior of concrete and the three modification factors was proposed.