Experimental Study On Compressive Fatigue Properties Of GO Concrete After Freeze-thaw And Sulfate Attack

Because of its low price,convenient materials,convenient construction,good overall performance and can be designed and adjusted according to the needs of the project,concrete has been widely used in the construction of various projects.At the same time,concrete has low tensile and deformation strength,internal microstructure has pores,cracks and other defects,in some special areas and harsh use environment,short service life and poor durability,so it is urgent to modify concrete to improve performance.Graphene oxide has a planar network structure and a high specific surface area.Adding it to cement-based composites can optimize cement hydration products and improve the microstructure,so as to improve the porosity and crack problems of cement-based composites.It is widely used in the experimental research of modified concrete.In this thesis,the effects of GO nanomaterials on the fatigue properties of concrete were studied,and the effects on the fatigue properties of GO concrete were determined under the two erosion environments of freeze-thaw cycle and sulfate dry-wet cycle,which provided references for further research on GO concrete.The research includes the following three parts:(1)The effect of adding 0.05% GO on the compressive fatigue property of concrete was studied.The results show that under uniaxial compression fatigue load,GO concrete has good integrity,and fatigue failure does not show obvious brittleness.Go can increase the compressive strength and fatigue life of concrete,and the fatigue life conforms to the Weibull distribution of two parameters,and the fatigue equation under different guarantee rates is obtained.The axial compressive fatigue strength corresponding to the fatigue life of 2 million times was obtained.Go could significantly enhance the axial compressive fatigue strength of concrete.The microstructure characterization by SEM shows that the internal structure of concrete can be improved by adding GO,reducing cracks and pores,and making the structure more compact.(2)The influence of dry and wet sulfate cycling on the compressive fatigue properties of GO concrete was studied.It was found that the compressive strength fatigue life and axial compressive fatigue strength of GO concrete decreased with the increase of the number of dry and wet sulfate cycles.The fatigue life of GO concrete after sulfate dry and wet cycling conforms to the Weibull distribution of two parameters,and the fatigue equations under different guarantee rates are obtained.The microstructure characterization by SEM showed that GO could slow down the rate of sulfate erosion,and the accumulation of fatigue damage was accelerated by the pores and microcracks caused by the expansion damage of erosion products.(3)The effects of freeze-thaw cycles on the fatigue properties of GO concrete were studied.The results show that the apparent damage of GO concrete increases with the increase of freezing and thawing times,but the integrity of GO concrete remains good,and the mass loss rate is less than 1%,which meets the requirements of frost resistance.The fatigue life of GO concrete after freeze-thaw cycle conforms to the Weibull distribution of two parameters,and the fatigue equations under different guarantee rates are obtained.The axial compressive fatigue strength corresponding to the fatigue life of2 million cycles decreases with the increase of the number of freeze-thaw cycles.Microstructure characterization by SEM shows that GO can slow the increase,diffusion and penetration of cracks in concrete under freeze-thaw cycle,but the freeze-thaw damage is aggravated under long-term freeze-thaw cycle,which also accelerates the accumulation of fatigue damage.