Study On Mechanical Behavior Damage Of Limestone Powder-high Volume Fly Ash Concrete Members Under Salt Freezing

Under the advocacy of the concept of sustainable development,the method of producing concrete with solid waste admixture replacing traditional cement has been popularized.Limestone powder-high volume fly ash concrete has been widely used in civil engineering due to its good energy-saving benefits and performance.With the increasing complexity of concrete engineering environment,under the action of climatic conditions and hazardous substances in environmental factors,the problem of "disease" of concrete happens prematurely,especially the phenomenon of concrete frost heave cracking and reinforcement corrosion caused by freeze-thaw damage and salt erosion,which leads to the degradation of the mechanical performance of concrete structure and seriously threatens the safety and durability of concrete engineering.As the important parameters to evaluate the durability of concrete,scholars at home and abroad have carried out systematic research on the frost resistance and salt corrosion resistance of cement concrete and aerated concrete,but pay less attention to the frost resistance and salt corrosion resistance of limestone powder-high volume fly ash concrete under the action of freeze-thaw cycle and salt freezing.In this paper,the test conditions are designed according to the soil environment and climate conditions in the western region of Jilin Province.The types and amount of soluble salts in saline soil in Da’an are selected to configure composite salt erosion solution.The mix proportion of limestone powder-high volume fly ash concrete with strength grade of C30 is selected,the fabrication size is of 120mm×120mm×120mm concrete pull-out member and size of 120mm×120mm×600mm concrete compression member,the damage law of mechanical behavior of limestone powder-high volume fly ash concrete members under salt freezing is studied from two aspects of binding stress of reinforcement and concrete and bearing capacity of concrete.The main research work and conclusions in this paper are as follows:1.The results of the bind performance test of limestone powder-high volume fly ash concrete members after salt erosion freeze-thaw cycle show that: The concrete on the surface layer of the member peels off and even the aggregate is exposed.The mass loss rate of the member decreases first and then increases with the increase of the number of salt freezing cycles,but the mass loss rate of the member does not decline in the composite salt solution with a mass fraction of 10%,and the concrete peeling is more serious.The relative dynamic elastic modulus curve of the member increases first and then decreases with the increase of the number of salt freezing cycles,and the higher the mass fraction of the composite salt solution,the faster the relative dynamic elastic modulus of the member decays.In the pull-out test after salt freezing,the components are mainly split and broken.In the composite salt solution with mass fraction of 3.4%,the components appear split pull-out failure,The bond stress between reinforcement and concrete decreases with the increase of salt freezing cycles,and the higher the mass fraction of salt solution,the faster the binding stress attenuation.2.The results of bearing capacity test of limestone powder-high volume fly ash concrete members after salt erosion freeze-thaw cycle show that: The concrete on the surface layer of the member peels off and the aggregate is seriously exposed.The mass loss rate of the member decreases first and then increases with the increase of the number of salt freezing cycles,but the mass loss rate of the member continues to rise in the composite salt solution with a mass fraction of 10%,and the damage degree of the member is large.The relative dynamic elastic modulus of the component increases first and then decreases with the increase of the number of salt freezing cycles,and the higher the mass fraction of the composite salt solution,the faster the relative dynamic elastic modulus of the component decays.In the axial compression test of members after salt freezing,the crushing of concrete leads to the destruction of members.With the increase of the number of salt freezing cycles,the number of cracks on the surface and the amount of concrete falling also increase.The ultimate bearing capacity of members shows a degradation trend with the increase of the number of salt freezing cycles,and the higher the mass fraction of salt solution,the faster the degradation of bearing capacity.3.By fitting the data obtained from the pull-out and compression tests of limestone powder-high volume fly ash concrete members after freeze-thaw cycle and salt freezing,the numerical calculation models of binding stress and bearing capacity of limestone powder-high volume fly ash concrete members under freeze-thaw cycle and salt erosion freeze-thaw cycle are obtained respectively.