Properties Of Cement-based Materials Modified By Graphite/EVA

With the implementation of the national “The Belt and Road” and coastal development strategies and the needs of national defense construction,the service environment of cement and concrete projects has become increasingly complex and harsh,and its durability problems have become increasingly prominent.In order to make cement-based materials used in more complex environments,improving the performance of cement-based materials,especially their durability,has become the focus of research in the field of cement concrete.Currently,graphene and carbon nanotubes have become the focus of research on improving the mechanical properties and durability of cement-based materials due to their catalytic ability for cement hydration and good corrosion resistance.However,due to its high price,it is limited to be used as a cement additive,while flake graphite is affordable and has good corrosion resistance.It may also improve the mechanical properties and durability of cement-based materials.Therefore,this paper considers the preparation of graphite cement-based materials by high energy ball milling method and combines with common additives of cement-based materials EVA,in order to explore the new path of cement-based materials modification.In this paper,the influence of graphite content on the physical and mechanical properties of cement-based materials was studied by high energy ball milling method.It was further modified by adding EVA and early strength agent.Sulfate resistance and frost resistance were studied by long-term soaking and slow freezing.The hydration process and microstructure were analyzed by the test methods of hydration heat,XRD,SEM and EDS.The conclusions are as follows:(1)With the addition of graphite,the fluidity of the cement-based material decreases and the standard consistency water consumption increases;When the graphite content was less than 0.4%,the setting time of the cement-based material was shortened and the strength was improved.When the graphite content was higherthan 0.4%,the strength decreased.The incorporation of EVA increased its fluidity,reduced the amount of water used for standard consistency and improves the flexural strength,but it also prolonged the setting time and reduced the compressive strength;When EVA content was lower than 2%,the strength of EVA cement-based material increased slightly;when EVA content was higher than 2%,the strength decreased with the increase of EVA content.After compounding,When the graphite content was no more than 0.4% and the EVA content was less than 2%,the water consumption for the fluidity and standard consistency of cement-based materials was reduced,and the initial and final setting time were prolonged.After 28 days,the strength first increased and then decreased.The strength reached reached the highest maximum of 10.73 MPa and 82.3MPa.when the graphite content was 0.4% and the EVA content was 1%.(2)Durability research results shown that: when the graphite content was not more than 0.4% and the EVA content was less than 2%,it could improve the sulfate resistance of cement-based materials.The strength of cement-based materials at 30 d and 90 d of erosion curing had been improved to some extent.With the increase of curing age,the corrosion resistance coefficient was higher than that of the blank group.(3)The test results of the hydration heat of cement shown that when the graphite content was lower than 0.4%,it could promote the hydration of cement and speed up the hydration heat release rate;When the EVA content was higher than 2%,it could delay the hydration of cement and reduce the hydration heat release rate.XRD analysis shown that the incorporation of graphite was conducive to the crystallization and grained growth of calcium hydroxide,and EVA would generate calcium acetate,resulting in a decrease in the production of calcium hydroxide.SEM and EDS observation analysis showed that the graphite evenly dispersed in the cement matrix,and existed in the form of folded,curled,interlaced and other lamellar structures.Its width was about 3-15?m,and its thickness was about 0.2?m.In the cement hydration matrix,the number of cracks was small and the width was narrow.The polymer filmproduced by EVA crossed over the cement,which increased the compactness of cement-based materials and reduced the porosity.