Performance Research And Ultrasonic Test On Reactive Powder Concrete After High Temperature

Reactive powder concrete(RPC)is a new-type cement-based material,which is characterized by high strength,large toughness and excellent durability.RPC has become the focus of research in the field of construction.In this paper,based on the existing research on high temperature performance and nondestructive testing of concrete,the explosive spalling properties,compressive properties and microstructure,ultrasonic test after elevated temperature were carried out.The main work of this paper is as follows:(1)Through high temperature test,explosive spalling rules,variation of appearance and mass loss with temperature properties of RPC was studied.The critical cracking temperature of RPC with different steel fiber content is different.Mixing with steel fiber volume dosage of 2.5%can effectively prevent RPC spalling.With the temperature increases,the appearance characteristics of steel fiber-reinforced RPC have same vary trend:color variation from slate-gray to brown-gray,then yellow-white,percussing sound from crisp to deep,surface crack increasing gradually.The mass loss increases gradually with the increasing temperature,and the rate of rise is more and more rapidly,then slow down.When the fiber content changes,mass loss of RPC changes little.(2)The cube compression tests of RPC were carried out after undergoing high temperature.The results indicate that as the temperature goes up,cube compressive damage rule of RPC with different steel fiber content are similar,and the compressive strength increases before 300? and then decreases.The brittle failure is occurred at normal temperature.With the temperature increases,more high temperature damage result in the decrease of strength sharply,and the crushing procedure shows more and more plasticity,after 500 ? especially.Comparing three kinds of concrete,normal concrete(NC),high strength concrete(HSC)and RPC,the relative compressive strength of RPC after elevated temperature is the highest,NC times,HSC minimum.There is size effect in the compressive strength of RPC after high temperature.The greater the size is,the greater the probability of high temperature damage occurs and the lower the strength is.(3)By scanning electron microscope(SEM)technique,the microstructure changes of RPC after different temperatures were studied.The results show that with the increase of temperature,the internal defects of RPC begin to accumulate,the cracks at the bonding interface of fiber and matrix come into being gradually,the microstructure deteriorate constantly and the loss of compressive strength increase continually.(4)The ultrasonic test of RPC after high temperature was carried out.The results indicate that with the variation of fiber content,ultrasonic velocity of RPC changes little at the same temperature.When the temperature increases,the ultrasonic velocity of RPC shows a descending trend,but the change of ultrasonic amplitude and frequency is not obvious.Adopting the parameters of damage degree and relative velocity to evaluate the performance of RPC after high temperature was better than the parameters of relative frequency and relative amplitude.The correlation of the fitting value of damage degree and the experimental value is the largest,which can accurately reflect the damaged degree of RPC.On the contrary,the fitting value of relative frequency and relative amplitude shows less correlation with the experimental value,and there are errors with assessments.The correlation of RPC between ultrasonic velocity and compressive strength after high temperature is existent,and the corresponding equation is established through regression analysis.