Experimental Study On Interfacial Bonding Properties Of Precast Concrete Members For Vertical Joints

The construction method gradually changed from cast-in-place system to prefabricated assembly with the development of building industrialization.Concrete pouring of vertical joints of prefabricated components is an important part of the overall performance and quality of the assembled structure.The bonding performance of the interface between the jointed concrete and the component is a difficult problem.This subject adopts the prefabrication and post-casting interface split-pull test method.First,the required concrete strength was prepared according to the benchmark mix ratio of the general subject group.Then the influence of the bonding performance was analyzed such as the strength of the post-concrete(C30,C35,C40,C45),interface treatment method(natural cast,closure mesh,water exposed aggregate),the use of interface agent(with or without interface agent)for optimizing the test results.Finally,quantitative analysis was conducted on the washed and exposed treatment surface through sand replacement method to study the influence of different ages(14d,28 d,56d,90d)of precast components on the bonding splitting performance,and give suggestions for the project.The specific research work and the main achievements are as follows:(1)The precast ordinary concrete(C30,C40)and post-cast self-compacting concrete(C30,C35,C40,C45)was prepared,and post-cast concrete with 10% expansion agent.The working performance and basic mechanical properties of concrete meet the test requirements.(2)The improvement of bonding performance was benefited by the increasing of the strength grade of post-cast concrete.The interface bonding strength increases with each increase of concrete(C30,C35,C40,C45)strength level by 7.4%,13.8% and 5.3%respectively.However,increasing the strength level of post-cast concrete has little effect on the growth of bond strength.From the perspective of engineering economy,the post-cast concrete was recommended for one strength level increased compared with precast concrete;the surface treatments of precast components were the key to the interface bonding strength.The bonding strength was largely influenced by different interface treatment methods.The effect of washing the exposed surface is the best(close to the split strength of the cast-in-place concrete)followed by the closing net,and the natural vibration surface is the smallest;the use of interface agent helps the interface bonding performance,and the interface bonding strength is increased by 1.0% to 13.2% compared with no use.Considering one more process and limited operating space,it can be used as an auxiliary treatment in the project and not recommended for large areas.(3)Different explicit depths can be obtained by using different amounts of washed rough surface agent.The roughness of the sand grouting test is between 4mm and 8mm.The bond strength of precast and post-cast concrete increases with the increase of roughness.The roughness of the prefabricated components was relatively good above 7mm,and the exposed depth was easy to be controlled at about 1/3 of the maximum particle size of the coarse aggregate.The bond strength was highest at 14 d,but the concrete performance was not stable,so 28 d was relatively good.