Study On Properties Of Ultra High Performance Cement-based Materials Modified By Graphene Oxide

Concrete plays a vital role in the construction of the country,However,the poor durability of the ordinary concrete in the corrosive environment often leads to its early destruction.As a new type of cement-based material,Ultra-high performance cement-based materials?UHPC?show excellent mechanical properties and durability,through surface hardening technology,UHPC can be used as the protective layer of ordinary concrete,which can reduce the erosion and damage of concrete by external corrosion ions and improve the durability of the concrete.Studies have shown that nano-materials can optimize the microstructure of cement-based materials and improve the strength and durability.Graphene oxide?GO?is a two-dimensional nanomaterial,its surface has a lot of oxygen-containing functional groups,so GO has good hydrophilicity and can be used as a reinforcing phase in Ultra-high performance cement-based materials.However,the shortcomings of ordinary UHPC,such as large viscosity and poor workability,will cause difficulties in construction and the decline of material density.Therefore,the self compacting UHPC mix ratio was designed in this paper to reduce the adverse effects caused by the insufficient working performance of UHPC.In the present study,the effects of raw materials on mechanical properties and workability of UHPC were studied from the five aspects of quartz sand gradation,mineral admixtures,water-binder ratio,superplasticizer,fiber type and quantity.The effect of GO on the hydration of Portland cement was analyzed by means of XRD,TG-DSC,SEM.GO was introduced into the UHPC system.The workability,mechanical properties and durability of UHPC modified by GO was studied emphatically.The following conclusions are obtained:?1?When quartz sand gradation is 3:4:3:0,water-binder ratio is 0.2,and superplasticizer content is 1.5%,UHPC has both good workability and mechanical properties.When the silica fume content increases from 15%to 25%,the strength of UHPC does not change significantly,but the fluidity loss is severe.Incorporating appropriate amount of FA2000 can significantly improve the UHPC fluidity without affecting the strength of UHPC,the best dosage is 10%-15%.The use of superfine slag to replace the appropriate amount of FA2000 can increase UHPC's strength,and has little effect on fluidity,the best dosage is 5%.The incorporation of steel fibers and PVA fibers can improve the UHPC's mechanical properties and the ratio of flexural strength to compressive strength.Compared with PVA fibers,steel fibers have smaller influence on UHPC's self-compacting performance,steel fibers are more suitable for the preparation of self-compacting UHPC.?2?The test results of XRD,TG-DSC and SEM showed that the addition of GO can promote the hydration of cement,increase the amount of hydration products,and optimize the microstructure of cement-based materials.In addition,GO can improve the mechanical properties of UHPC and the improvement of early strength is more obvious,but the addition of GO reduced the fluidity of fresh UHPC paste.When the GO content increased from 0.03%to 0.05%,the UHPC's strength did not change obviously,but the fluidity decreased significantly.?3?GO can improve the resistance to chloride ion penetration of UHPC,the addition of 0.03%GO can reduce the chloride diffusion coefficient of UHPC by14.5%to 2.12×10^-13m²/s.The UHPC modified by GO has more excellent erosion resistance.When the double erosion age of sulfate and magnesium salt increased to150 days,the resist corrosion coefficient of UHPC without GO droped to 0.94,while the resist corrosion coefficient of UHPC modified by GO was still above 1.00.The early drying shrinkage of UHPC is larger,after 28 days,the change in the drying shrinkage rate of UHPC is not obvious,GO and steel fibers can reduce the drying shrinkage rate of UHPC.Incorporating 0.03%GO can increase the tensile bond strength of the UHPC by 17.3%,steel fibers also have a certain effect on the tensile bond strength of UHPC.