Study Of Cement-based Materials By The Mixture Of Graphene And Carbon Fiber

Cement-based material is a kind of porous brittle material,which will inevitably cause cracks and local damage when used.Through these pores and micro-cracks,water and other harmful substances enter the interior of cement-based materials,causing a series of adverse effects on the internal structure,such as strength reduction,leakage,carbonization,steel corrosion and so on.This not only affects the beauty of the building,but also affects its strength and durability.This results in a decrease in construction strength and service life.Therefore,it is of great significance to improve the strength and durability of cement-based materials.Recent studies have shown that graphene and carbon fiber can effectively improve the mechanical properties and durability of cement-based materials.Both graphene and carbon fiber have properties of high strength and high modulus.Adding carbon fiber into concrete can effectively inhibit the cracking of cement-based materials and improve the strength.Graphene can be packed into tiny pores,increasing the compactness of cement-based materials and improving their impermeability.Moreover,carbon fiber and graphene have good electrical conductivity,which can improve the effect of electrodeposition to repair the cracks in cementbased materials.In this study,the modification of mechanical properties and durability of concrete was studied by mixing graphene and carbon fiber,as well as its promoting effect on the repair of mortar cracks by electrodeposition method.The modification mechanism of carbon fiber and graphene to cement-based materials was also described.The main findings are as follows:(1)Carbon fiber and graphene effectively improve the mechanical properties of concrete.The optimal content of carbon fiber is 0.6% when adding carbon fiber alone.The compressive strength of concrete is increased by 18.9% and the flexural strength by 25.7% at the age of 28 days.The optimal content of graphene is 0.06% when graphene is added alone.The compressive strength of concrete increased by 16.0% and the flexural strength increased by 19.4% at the age of 28 days.The strength was highest when the carbon fiber content was 0.6% and the graphene content was 0.08% at the situation of Carbon fiber and graphene were mixed.The compressive strength of composite concrete was increased by 11.1% and the flexural strength by 14.5% compared with that of single-mixed carbon fiber concrete.Carbon fiber inhibits the generation and development of microcracks and graphene improves the shape and distribution of cement hydration products in concrete,which further improves the mechanical properties of concrete compared with a single admixture.(2)Concrete durability can be effectively improved through graphene and carbon fiber composites.Carbon fiber has good crack resistance,which reduces the content of harmful holes in concrete.Filling effect and formwork effect of graphene increase the compactness of cement stone and reduce the porosity of concrete.When the carbon fiber content is 0.6%,the chloride ion migration coefficient of concrete at the age of 28 days decreases by 48.0%,and the compressive strength of concrete after 200 freeze-thaw cycles increases by 64.4% compared with the control sample.The concrete has the best impervious and antifreeze performance when carbon fiber and graphene are combined.The chloride ion migration coefficient of concrete was reduced by 51.6% at the age of 28 days,and the proportion of harmful holes and multiple harmful holes was reduced by 44.1% compared with the concrete of single-doped carbon fiber.After 200 freeze-thaw cycles,the mass loss rate decreased by 35.3%,the relative dynamic elastic modulus increased by 12.9%,and the compressive strength increased by 11.3%.It shows that the composite mixing of carbon fiber and graphene can improve the internal structure of concrete,reduce the generation of pores and microcracks,improve the compactness of concrete,and thus improve the durability of concrete.(3)The electrochemical deposition method for repairing mortar cracks was improved by using the conductive properties of carbon fiber and graphene.The study found that the mortar crack finally healed after 20 days of current was applied,and the crack repair speed was the fastest in the first 5days,and then the speed gradually slowed down.Both carbon fiber and graphene can accelerate the process of fracture repair.The mortar mixed with carbon fiber and graphene had the fastest crack repair,and the cracks had healed at 15 days.The quality of the deposited product increased by 114.9% compared with the blank sample.The permeability coefficient of chloride ion decreased by 71.9%.The propagation time of ultrasonic wave was reduced and the amplitude was increased by 170.4%.It was found by SEM that most of the precipitation products generated in the blank sample were loosely arranged and irregular,with poor compactness.However,the sedimentary products in the carbon fiber and graphene mixed samples interweave to form a uniform and dense structure,repairing effectively the cracks in the mortar and improving the anti-permeability.