Experimental Study And Highly Detailed Simulation Analysis Of Electrically Conductive Roller Compacted Concrete In The Alpine Region

At present,the focus of dam construction in China has gradually shifted from the central and eastern regions to the alpine regions with extremely rich hydropower resources and low development level.The environment in the alpine regions is characterized by large temperature difference,low extreme temperature,long winter break,high wind power grade and dry climate,especially the winter break lasting nearly half a year has brought severe challenges to the temperature control and crack prevention of the overwintering layer of concrete dams.Although China has made outstanding progress in temperature control of concrete dams,the experience accumulated by dam workers at home and abroad in dam construction in areas with severe natural conditions is still insufficient.External thermal insulation measures are still the main measures to prevent the loss of heat on the dam surface,so it is difficult to effectively compensate the heat loss through the internal heat generated by materials,and it is difficult to fundamentally solve the problem of temperature control of roller compacted concrete dams in alpine regions.Conductive concrete has already made its debut in engineering because of its good mechanical properties and excellent electrothermal properties.However,this kind of material will reduce the fluidity of concrete due to the addition of hydrophobic conductive phase materials,which will lead to poor casting effect.In this paper,based on the design idea of conductive concrete,the conductive concrete materials suitable for rolling process are put forward,and the forming quality improvement measures are put forward from the angle of material design and construction.The microstructure design,temperature control effectiveness and engineering feasibility analysis of rolled conductive concrete are carried out in depth,and the research on application effect evaluation is carried out based on the RCC dam project in alpine region of China.The main research contents and research results are as follows:(1)The interaction potential energy between particles in conductive cement slurry system is calculated by using EDLVO theory,and it is clear that the aggregation of carbon black particles is the main reason for the poor fluidity of cement slurry;Through dispersion test and Scanning electron microscope,SEM),the effect of adding sodium dodecyl sulfate(SDS)into aqueous solution and cementitious system on the dispersion of carbon black was evaluated,and the modification of carbon black particles was realized,which provided reference for the mix design and optimization of roller compacted conductive concrete materials.(2)The resistivity calculation model of roller compacted conductive concrete is established,and the correlation between resistivity and aggregate volume fraction,carbon black content,curing age,electric field intensity and external load is analyzed.The electrothermal temperature rise test of large-scale rolled conductive concrete specimens with the size of 3000 mm × 700 mm × 200 mm was carried out,and the variation law of internal and surface temperatures of large-scale specimens with time after electrification was analyzed,which verified the effectiveness of temperature control of the overwintering layer poured by rolled conductive concrete.(3)The rolling test of newly-mixed roller-compacted conductive concrete was carried out,and the variation laws of surface settlement and compaction index with rolling times were analyzed.According to the principle of unit compaction work and the rolling times measured by the test,the rolling times of field equipment under different conditions were deduced.The macro-scale mechanical properties tests of compressive strength,tensile strength and shear strength were carried out for core samples,and the distribution law of void ratio was quantitatively analyzed by X-ray tomography test.The multi-scale performance test can fully reflect the performance changes after mixing,rolling and curing hardening,and provide reference for the design,construction and service of ERCC.(4)Using numerical calculation results and material test results of ERCC specimens obtained by X-ray tomography,the simulation damage parameters of ERCC were calibrated;The fine simulation analysis of ERCC was carried out by coupling continuous medium and discontinuous medium calculation method,and the ERCC meso-model was established.The fine numerical simulation method of RCC based on real aggregate shape was put forward,which made it clear that the volume content of aggregate could improve the mechanical properties of ERCC to a certain extent,and the selection of appropriate aggregate content in engineering could ensure both the electrothermal and mechanical properties of ERCC.(5)Considering the sharing of ERCC and RCC,based on the theory of interface mechanics,the deformation coordination evaluation index of dissimilar materials is obtained by solving the characteristic equation of stress singularity,and the validity of the deformation coordination evaluation index is verified by numerical calculation.The influence mechanism of interface parameters(elastic modulus,Poisson’s ratio and bonding angle)on deformation coordination is revealed.The greater the difference in mechanical properties of dissimilar materials,the stronger the singular stress at the interface,which is not conducive to the coordinated control of structural deformation.Combined with the interface form in practical engineering,the paper puts forward guiding opinions for the design of high concrete partition structure.(6)In order to ensure the flexible control of the electrothermal temperature rise of ERCC overwintering layer,the refined power supply mode and optimization method are put forward,and the reliability of the U-?T quantitative model of the temperature difference between inside and outside the dam body and the electrified voltage needed to resist cold wave is deduced and verified.Relying on the RCC gravity dam project in alpine region,through the calculation of the temperature field of RCC dam with ERCC overwintering layer during the construction period,it is proved that it is more applicable to use RCC in overwintering layer and adopt a reasonable power supply mode,which can provide a new research idea for solving the temperature control and crack prevention of concrete dam in alpine region.