| Reactive powder concrete(RPC)has excellent properties such as ultra-high strength and high durability,but its brittleness is large,in consideration of the hoop action of steel tube,the RPC filled steel tube is prepared.However,the RPC has a large amount of shrinkage due to low water binder ratio,no coarse aggregate and other reasons,which deteriorates the interfacial performance between RPC and the steel tube,which is difficult to play the interaction of them.This also limits the application of RPC filled steel tube in practical projects.To solve the above problems,combining with the empirical formula and test results,mix proportion of RPC is determined,shrinkage mechanism is proved,the method is proposed to solve the problem of large shrinkage,micro-expanded RPC is prepared with excellent mechanical properties,microscopic testing technology is uesd to study and analyze the microstructure,hydration product composition,etc.,RPC filled steel tube was prepared,and its expansion performance,interface combination performance,and axial compression performance were analyzed.This paper relies on the National Key Research and Development Plan(No.2017YFB0310000)and the National Natural Science Foundation of China(No.51772226)to carry out the main work and achievements as follows:(1)Based on the maximun packing density calculation model,the mixture ratio of cementitious material of RPC was determined.The influence of water to binder ratio,sand to binder ratio,maximum aggregate size,steel fiber content and superplasticizer content on the basic mechanical properties of RPC was studied through mechanical tests.The results show that reducing the ratio of water to binder,increasing the amount of steel fiber and controlling other variables can improve the compressive strength and flexural strength of RPC,the mixture ratio of RPC was determined.The axial compression tests of RPC show that RPC has good mechanical properties.Because of the toughening effect of steel fiber,the brittleness of RPC is much better than that of ordinary concrete.(2)The effect of expansive agent on the properties of RPC was studied.The results showed that the early strength of RPC was increased by adding an expansive agent,and RPC shrinkage was compensated to a certain extent,but it did not slow down the relative humidity.By introducing the internal curing technology and using the pottery sand with water storage function,the micro expansion RPC was successfully prepared by the combined action of expansive agent and pottery sand,and its mechanical properties were excellent.Thermal analysis,SEM,XRD and other testing techniques were used to study the microstructure and the expansion mechanism of the microexpanded RPC.The results show that the microstructure of the micro-expanded RPC sample has a high degree of compaction,and the interface between the aggregate and the cement stone is tight.(3)The basic mechanical properties of the RPC filled steel tube were tested.The results showed that: with the addition of expansion agent and steel fiber in a certain range,the expansion rate of the RPC filled steel tube could be increased.The interfacial adhesion test shows that the amount of expansion agent and steel fiber has a great influence on the interfacial bonding properties.With the increase of the content,the bonding strength is obviously improved,and the bonding strength of different age samples increased with the increase of age.The short column axial compression test shows that the expansion agent and the amount of steel fiber have great influence on the compressive strength.The expansion agent improves the synergistic effect between the steel tube and the concrete,so that the synergistic effect between the steel tube and the core concrete is enhanced,and the axial compression bearing capacity of the RPC filled steel tube is improved.The finite element analysis of the RPC filled steel tube shows that the obtained results can reflect the failure form and ultimate load of the RPC filled steel. |
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