Enhancement Effect And Reinforcement Mechanism Of Graphene Derivatives On Mechanical Properties Of Coastal Cement Soi

The foundation engineering and geotechnical engineering construction in coastal areas have an important impact on the development of social economy.In recent years,the development of a large number of engineering construction projects has led to the continuous shortage of land resources,so the reinforcement of coastal soft soil has begun to receive widespread attention.However,the application of coastal soft soil has been greatly limited due to its own performance defects,and the soft soil reinforcement technology has also become the current research focus.Cement as the basic cementing material has been widely used in practical projects,but cement soil is facing great challenges due to its high brittleness and multiple cracks.As a new nano-material,graphene derivatives began to be used in cementbased materials with breakthrough,and showed good performance advantages.In this study,three kinds of graphene derivatives,namely,large-sized graphene oxide(referred to as "LG"),small-sized graphene oxide(referred to as "SG")and enhanced graphene oxide(referred to as "EG"),were mixed into coastal cement soil(referred to as "CS")to obtain three kinds of graphene derivatives reinforced coastal cement soil specimens(referred to as "LGCS","SGCS" and "EGCS").Through unconfined compressive strength test,triaxial shear test,dry-wet cycle test and a series of micro tests,the enhancement effect and reinforcement mechanism of graphene derivatives on mechanical properties of coastal cement soil were explored.The main results of this study are as follows:(1)The unconfined compressive strength characteristics of coastal cement soil can be improved by adding graphene derivatives.At the same curing age,the compressive strength,failure strain and elastic modulus of LGCS,SGCS and EGCS specimens increased gradually with the increase of the content of LG,SG and EG,and reached the maximum when the content was 0.05%.Meanwhile,LG,SG and EG can also improve the residual strength and brittleness index of LGCS,SGCS and EGCS specimens.And EG had the best effect on the unconfined compressive strength characteristics of coastal cement soil,followed by SG,and LG had the worst effect.(2)Adding graphene derivatives can improve the triaxial shear strength characteristics of coastal cement soil.LG,SG and EG can effectively improve the shear strength and residual deviatoric stress of coastal cement soil.Under the same confining pressure and age,the shear strength and residual deviatoric stress of LGCS,SGCS and EGCS specimens increased with the increase of the content of LG,SG and EG,and both reached the maximum when the content of LG,SG and EG was 0.05%.Meanwhile,LG,SG and EG can also increase the internal friction angle and cohesion of coastal cement soil.And EG had the best effect on improving the triaxial shear strength characteristics of coastal cement soil,followed by SG,and LG had the worst effect.(3)Adding graphene derivatives can improve the dry-wet cycle resistance of coastal cement soil.With the increase of the number of dry-wet cycle,the mass increased and porosity of CS,LGCS,SGCS and EGCS specimens decreased first and then increased,the axial and radial dimensions increased first and then increased and then stabilized,while the unconfined compressive strength increased first and then decreased.With the increase of the content of LG,SG and EG,the mass,axial and radial dimensions of LGCS,SGCS and EGCS specimens increased gradually,while the unconfined compressive strength increased gradually.Moreover,EG can effectively improve the dry-wet cycle resistance of coastal cement soil,followed by SG,and LG had the worst effect.(4)Graphene derivatives had an important influence on the phase composition and content,orientation index,element composition and content and microstructure of coastal cement soil specimens,but had relatively little influence on the molecular structure and groups.Graphene derivatives will not affect the types of cement hydration products and element compositions,but can effectively reduce the orientation index and Ca/Si of coastal cement soil specimens,while increasing the weight ratio of Si.Graphene derivatives can significantly reduce the number and size of pores in coastal cement soil to a certain extent,and can also induce the morphology of cement hydration products,resulting in lamellar,flower,membranous and polyhedral crystals.Graphene derivatives can also produce strong interfacial force,nucleation effect,template adjustment and other effects on cement hydration products,so as to finally form a more stable,dense and even microstructure of coastal cement soil.Among the three graphene derivatives,EG had the best promotion effect on cement hydration,followed by SG and LG.