Experimental Study On Dynamic Mechanical Properties Of RCC Under Low Temperature

Roller compacted concrete(RCC)is a kind of dry hard concrete with poor cement,which is widely used in hydraulic dam construction as an economical and practical building material.The RCC dams under construction or to be constructed in China are mostly located in the cold and earthquake-prone areas in the west.At present,the research on the dynamic mechanical properties of roller compacted concrete under low temperature environment is the weak point of the anti-seepage and anti-seismic center of hydraulic facilities.Compared with the normal concrete dam,the roller compacted concrete is constructed by vibration rolling method,and the number of internal pores is less,which has good frost resistance in theory.However,the internal slurry of roller compacted concrete may be unevenly distributed and the structure is not dense.Under harsh climatic conditions,the mechanical properties of roller compacted concrete will change,which poses a great challenge to the safety and stability of roller compacted concrete dams.Therefore,it is extremely urgent to carry out the experimental study on the dynamic mechanical properties of RCC under low temperature environment to provide a theoretical basis for the application and development of RCC dam construction technology in cold regions.In this thesis,the dynamic mechanical properties test and CT scanning test are combined.Taking different low temperature,different strain rate and different confining pressure as variable factors,constant temperature and humidity box,GCTS rock triaxial apparatus,industrial CT and other instruments are used to test.The failure mode,stressstrain curve,peak compressive strength change rule and microscopic damage characteristics of RCC specimens are obtained,which provide a reference for the study of dynamic mechanical properties of RCC under low temperature environment.The main conclusions are as follows :(1)Through the uniaxial dynamic compressive test of RCC under low temperature environment,the failure mode,stress-strain curve and peak compressive strength of RCC specimens under different low temperatures and different strain rates were studied.The results show that in the uniaxial dynamic compression test,the failure degree of RCC specimens increases with the increase of strain rate and decreases with the decrease of temperature.The peak compressive strength of RCC specimens increases with the increase of strain rate and the decrease of temperature.(2)Through the triaxial dynamic compressive test of RCC under low temperature environment,the failure mode,stress-strain curve and peak compressive strength of RCC specimens under different low temperatures,different strain rates and different confining pressures were studied.The results show that in the triaxial dynamic compression test,the failure degree of RCC specimens increases with the increase of strain rate,decreases with the decrease of temperature,and decreases with the increase of confining pressure.The peak compressive strength of RCC specimens increases with the increase of strain rate,temperature and confining pressure.(3)Through the CT scanning test,the scanning layer images and three-dimensional images of specific RCC specimens after test under different low temperatures,different strain rates and different confining pressures are studied.By analyzing the distribution characteristics of pore cracks in the specimen,the meso-damage and failure mechanism of RCC is studied.The results show that with the increase of strain rate,the number of pores and cracks increases and the distribution is scattered.With the decrease of temperature,the RCC specimen is more dense,the compressive strength is improved,and the number of pores and cracks is reduced.With the increase of confining pressure,the roller compacted concrete specimen is subjected to lateral constraint,and the number of pores and cracks is reduced,and the damage degree of the specimen is also relatively reduced.