Experimental Research On Different Repair Methods After Drilling Of Axially Compressed RC Columns

As the main method for detecting the compressive strength or internal defects of concrete,the core drilling method is widely used in practical engineering due to its scientific,intuitive and practical advantages.However,because the core drilling method has the disadvantages of causing concrete structures or components to be significantly damaged,the specification stipulates that the holes left by the drill core should be promptly repaired after sampling the cores.However,there is no clear provision for repair methods.In actual projects,due to limitations in testing costs,time,and technical capabilities,the relevant units cannot completely repair the faults in time according to the specification,or usually just fill in the holes,and the materials of filling holes and maintenance are not in place.The effect may be equivalent to Without being filled up,it will have an adverse effect on the bearing performance and even the seismic performance of structural members.Therefore,in this paper,through the axial compression test on the reinforced concrete short columns,the effect of whether the core hole is repaired and the different ways of repairing on the stress performance and bearing performance of the concrete column was studied.In order to ensure that the test conditions are closer to the actual engineering conditions,a new attempt of coring and repairing operation is adopted in this test.Three kinds of repair methods were studied in the experiment:1)No filling(in case of filling failure in simulation project)2)Pre-cast core plus structural glue to fill 3)micro-expansion fine stone concrete to fill.The micro-expansion concrete filling is a common core hole repairing method in the current engineering,and the pre-fabricated core plus structural adhesive filling has not been widely applied.Considering that the prefabricated core filling method is easy to operate and easy to obtain,the test focuses on analyzing the repairability of the component handling performance so as to comprehensively examine the superiority of this method compared with the filling of the slightly-expanded concrete in various aspects.The main contents are as follows:1.Sample template,reinforcement cage lashing,concrete pouring and curing were performed.Before the static load test,material properties tests of steelbarsandconcretewereconductedonaWAW-1000kN microcomputer-controlled electro-hydraulic servo universal testing machine.The ratio of strength to yield of steel bar is more than 1.25,and the steel has enough ductility;concrete cube compressive strength 28.15MPa,elastic modulus is.209?10~4N/mm~2.2.A total of 8 concrete short columns were fabricated and divided into 4groups.Each sample was independently tested for axial ultimate load carrying capacity.Z1 and Z2 are directly loaded to the core without core loading;Z3 and Z4 are loaded to 1500 k N and then cored,but not filled,and continued to be loaded until destroyed;Z5 and Z6 are loaded to 1000 kN for core loading,and cores are added immediately after core loading.After the glue is filled for 3 days,the load is continued until it is destroyed.When Z7 and Z8 are loaded to1000kN,they are loaded with cores.Immediately after coring,they are filled with micro-expanded fine stone concrete,and the load is continued for 3 days.The test was conducted on a 500T-YAW-5000 microcomputer-controlled electro-hydraulic servo press in the structural laboratory of Taiyuan University of Technology.The failure load,failure morphology,load-strain curve,and strain of steel and concrete after loading and unloading were recorded.Changes.3.Analyze and test the experimental data according to the experimental phenomena:(1)Core sampling will change the failure mode of reinforced concrete short column specimens,which will change the failure mode of the specimen from axial failure to the biased failure mode.The force mode will also change from the axial pressure to the small bias,after the core hole is repaired.These changes have been well restored to some extent.(2)The sampling of cores leads to the decrease of ultimate bearing capacity of reinforced concrete short column specimens,the increase of the ultimate axial displacement and the increase of the ultimate displacement ductility.The effect of repairing the core hole on the bearing capacity is better,but it has little effect on the axial displacement,which means that the core will reduce the ductility of the concrete column,which is not conducive to the earthquake resistance of the structure.(3)Filling the core hole is conducive to the repair of the column bearing capacity and force performance caused by the drill core.Although it cannot be completely restored,the damage caused by the core hole can be reduced.Among them,the prefabricated core filling method is more effective than the slightly-expanded concrete in repairing the bearing properties of the ultimate bearing capacity,ultimate displacement,and force mode.