Research On The Application Of Nano-silica In Polypropylene Fiber Concrete

With the sustainable development of contemporary cities,people pay more and more attention to urban underground space resources,while the traditional concrete structure can not meet the needs of underground engineering.At present,the mixed application of concrete and nanotechnology opens up a new way for developing advanced materials with advanced properties.In order to improve the strength and durability of concrete,people have done a lot of research and exploration,but ordinary concrete has been unable to meet the requirements of strength,durability,safety and low maintenance cost.These factors are very important for high-rise buildings,long-span bridges and many other concrete products.Adding fibers and nano particles into concrete can produce a new reinforced concrete composite material,which has high ductility,good density and durability,and has become one of the research hotspots.In this paper,nano-Si O₂ polypropylene fiber modified concrete was synthesized.Through compressive strength test,splitting tensile strength test,rapid freeze-thaw test and microstructure test(X-ray diffraction and scanning electron microscope),the modification effect and corresponding mechanism of polypropylene fiber concrete with different amount of nano particles were analyzed.The results are as follows(1)The compressive strength and splitting tensile strength of polypropylene fiber concrete will be enhanced with the increase of nano silica content(within a certain range of 0?2.7%)in the gradually increasing curing time,and the early strength will be improved significantly.The best content of nano silica is 2.7%.(2)In the early stage of freeze-thaw,because the mass loss rate changes very little,it can be seen that the effect of freeze-thaw cycle on the quality of polypropylene concrete is not significant.The relative dynamic elastic modulus of concrete in the same mix proportion will decrease with the increase of freeze-thaw cycles.When the content of nano-Si O₂ is 1.8%,the relative dynamic elastic modulus is the largest,which indicates that the frost resistance of concrete is the best.(3)X-ray diffraction(XRD)and scanning electron microscopy(SEM)were used to test the concrete specimens.It was found that there were quartz,calcium hydroxide,dicalcium silicate,tricalcium silicate,calcite and magnesium oxide in the concrete,and a small amount of low temperature quartz.Volcano ash effect of nano silica consumed calcium hydroxide crystal,facilitated hydration of cement,and C-S-H gel filled the pores of cement paste to improve the microstructure of concrete.On the other hand,nano-Si O₂ itself will also fill in the internal pores of concrete.Through these two ways,the compactness of concrete matrix can be improved,and the mechanical properties and frost resistance of concrete can be improved.