Study On The Shear Properties Of The Interface Between Old And New Recycled Concrete Under Freeze-Thaw Cycles

The aging of concrete buildings and the damage of concrete buildings caused by natural disasters will produce a lot of waste concrete.In order to alleviate the pressure of waste concrete on land resources and environmental protection,waste concrete can be used to reinforce and repair buildings.At present,in the reinforcement and repair of concrete structures,the constructors often deal with the concrete interface according to the engineering experience,so as to repair the damaged concrete buildings,however,cracks and spalling soon appeared in the concrete buildings repaired according to engineering experience in the cold regions of northeast China,the results show that the treatment of concrete interface in freeze-thaw environment based on engineering experience is not very ideal.Therefore,the shear behavior of the new-to-old interface of recycled aggregate concrete subjected to freeze-thaw cycles needs further study.Therefore,this paper will systematically analyze and research the shear strength performance of old and new interfaces of recycled concrete at normal temperatures and freezing and thawing cycles.The main research content is as follows:(1)The shear test of the old and new interfaces of recycled concrete was carried out by changing the replacement rate of recycled coarse aggregates of the concrete test sample,the rebar proportion of interfaces,the concrete strength level and the interface treatment mode(slotting and applying adhesion agent)at normal temperatures,indicating that:By changing the replacement rate of recycled coarse aggregates in the concrete test sample,and the failure load of the interface decreases by about 10% with each increase of the replacement rate of recycled coarse aggregate,the failure load of interfaces will decrease as the replacement rate of recycled coarse aggregates increases;the failure load of the interface will significantly increase as the rebar proportion of interfaces increases,and the overall performance of the test sample is improved significantly;the failure load of interfaces will increase as the strength level of the concrete increases,compared with C30 specimens,the failure load of C40 specimens is increased by about 20%;the failure load of concrete interfaces with slotting is far higher than that with roughing,and the adhesion agent on the concrete test sample can also effectively improve the failure load of new and old concrete interfaces,however,the increase is limited to about 3k N.(2)The concrete test sample interface shear test was carried out by changing the replacement rate of the recycled coarse aggregates of the concrete test sample,the concrete strength level and the concrete interface treatment mode(slotting and applying adhesion agent)under the action of freezing and thawing cycles,indicating that: When the number of times of freezing and thawing cycles is different,the failure load of the concrete test sample interface will decrease as the number of times of freezing and thawing cycles increases;When the number of times of freezing-thawing cycles is the same,by changing the replacement rate of recycled coarse aggregates of the concrete test sample,the failure load of interfaces will decrease as the replacement rate of recycled coarse aggregates increases;by changing the strength level of the concrete test sample,the failure load of interfaces will increase as the strength level of the concrete increases;by changing the interface treatment mode of the concrete test sample,the failure load of the interface will increase because of the application of the adhesion agent,however,the increase of the failure load on the interface is very small.