Experimental Study On Bahavior Of Ultra High Toughness Cementitious Composites Repaired Beam With Initial Notch

A kind of new high performance fiber reinforced concrete,Ultra High Toughness Cementitious Composites(abbreviated as UHTCC),which shows prominent toughness and superior durability has been successfully applied in many practical projects overseas.When the UHTCC members are used in repair system,except for the fundamental material mechanical properties of UHTCC and infrastructure,bond behavior of the interface between them and crack behavior under loading are urgently problems of durable structure design.Therefore, beam tests with different repair materials,different initial notch and using UHTCC as repair material are performed in this paper,with emphasis on the bond behavior and crack kink condition and trapping mechanism of UHTCC.Meanwhile,the system ductility,deformation capacity and the energy absorption capacity are tremendously improved.The major contributions are summarized as follows:1.The paper introduces the development background of the Ultra High Toughness Cementitious Composites and the inside and outside present applications firstly.then, exhausts the superior crack controlling capacity of UHTCC in briefly.2.Secondly the paper introduces the experiment on UHTCC executed by the Victor C. Li's researching team of the university of Michigan,simultaneously introduces the concept of crack trapping mechanism based on fracture mechanics,the theoretical analysis phenomenon,the design requirement of the specimen and loading condition.3.The followed experiments are according to about crack kink theory,selecting different material as repair material,such as steel fiber reinforced concrete,high performance mortar,pure concrete and UHTCC.with the same loading condition,the paper studied on the flexural behavior of the combine beams.On contrasting of the results, observing the phenomenon,we can know that the UHTCC repair system has superior deformation and energy absorption capacity and more strength.4.The paper presents the influence of surface preparation on the kink-crack controlling mechanism of combine beams,this demonstrates that the smooth surface system is preferable to the rough surface system,from the view point of obtaining the durable repair structure.The special phenomenon of kink-crack trapping which provides good serviceability without any major failure is best revealed when the substrate concrete is prepared to have the smooth surface prior to rough.5.This paper revealed the influence of the different initial notch on the interface,the fracture toughness of the repair systems differ according to different dimensions of specimens and boundary conditions.Then it can know that when the length of the initial notch is 50mm, the system has more deflection and energy absorption capacity.6.Beside the experiments above that using concrete as substrate,followed study on the UHTCC as repair material for UHTCC as substrate,the results revealed that the beam with 50mm initial notch length is prior to other dimensions in deformation and energy absorption capacity.7.The experiments in this paper provided fairly well verification for the crack kink trapping mechanism,expressed that if the repair material has R-curve behavior so that it have special crack controlling capacity.And then improved the ductility of the infrastructure and prolonged the life time of structure,thus economized the country economic.