Experimental Study On Impact Mechanical Properties Of Roller-compacted Concrete At Low Temperature

Roller compacted concrete(RCC)is one of the most widely used materials in water conservancy projects.In order to make full use of the water-energy resources in northwest China,RCCD is being planned and constructed in cold regions in western China one after another.However,natural disasters such as earthquakes and mudslides often occur in western China due to complicated terrain and harsh climate.The external load and lowtemperature environment have great influence on the safety and stability of the dam.Therefore,it is of great significance to carry out experimental research on dynamic characteristics of RCC under impact load.In this thesis,the strain rate effect and temperature effect of mechanical properties,crushing characteristics and energy dissipation are studied through dynamic compression test,dynamic splitting test and fragment screening test.The main research work and conclusions are as follows:(1)The dynamic compression test and dynamic splitting test were carried out on the low-temperature RCC samples at different temperatures and strain rates,and the mechanical parameters such as the stress-strain curve,peak strength,peak strain,elastic modulus,etc.The analysis was carried out,and the strain rate effect and temperature effect of various mechanical parameters were discussed.It is found that the peak stress,peak strain,and elastic modulus increase quasi-linearly with the increase of strain rate under the two loading methods,the peak stress growth rate is greater than the elastic modulus growth rate,and the peak strain growth rate is the smallest;peak stress,elastic modulus It increases linearly with the decrease of temperature,but the peak strain decreases linearly with the decrease of temperature,because the internal pore water freezes,the brittleness of concrete increases,and the deformation capacity increases,so that the deformation when the ultimate load is reached is reduced.(2)The samples after the dynamic compression test and the dynamic cleavage test were screened,and it was found that the fine particles,large particle size fragments,average particle size and fractal dimensions in the fragmentation characteristics under the two loading modes showed obvious strain rate effect and temperature effect,and the relationship between fractal dimension and average particle size was discussed,and it was found that the two were linearly related.For the equilibrium analysis of the crushing product set,in the dynamic compression test,there are certain staged strain rate effects and temperature effects in the uneven coefficient and curvature coefficient,but most of the curvature coefficients of the dynamic splitting failure specimens are greater than 2.5,which is worse than the continuity of the particle set of the dynamic compression crushing specimen.(3)In the dynamic compression test and dynamic splitting test,the incident energy,reflective energy,transmission energy and dissipation energy all increase linearly with the increase of strain rate,and the increase range is: the incident energy is the largest,the reflective energy is second,the dissipative energy is weak,and the transmission energy is the smallest;At the same time,the dissipation rate and transmittance increase linearly with the increase of strain rate,but the reflectivity shows a linear trend.Transmission energy and dissipation energy increase with the decrease of temperature,but reflective energy gradually decreases with the decrease of temperature;The dissipation rate and transmittance show an increasing trend,but the reflectivity shows a downward trend,because the temperature decreases,the overall strength of the specimen increases,and under the same impact load,more energy is required to expand the micro-fissure in the specimen.The correlation between energy dissipation and macroscopic destruction is analyzed,and the specific energy dissipation increases with the increase of strain rate.The fitting results of specific energy dissipation-peak stress and specific energy dissipationfractal dimension are ideal,and the fitting correlation is high,and the rationality of the fitting function is verified,indicating that the specific energy energy consumption of the specimen has a strong strain rate correlation with peak stress and fractal dimension.