Highway Subgrade Nano Composites Solidified Soil Experimental Study

If we solidify the mucky soil and use it as highway subgrade soil,its mechanical performance will directly affect the pavement performance of road structure.Due to the strength of cement soil is not so high,its deformation is large and it is very easy to crack,the application of it in highway engineering will be certainly restricted. So the study of improving the mechanical properties of cement stabilized soil and raising its pavement performance as highway subgrade soil is very important for improving the using condition of pavement structure and prolonging its service life.In this paper I added different proportions nano SiO₂ and nano Al2O₃ in cement soil in order to study the solidification effect in cement soil of two kinds of nano materials and the modification effect in cement soil when they were added together.I made a research on cement soil's mechanical properties under different adding amount of nano SiO₂ and nano Al2O₃ through indoor unconfined compressive strength test and split test.I also study the microcosmic mechanism when nano materials modified cement soil by scanning electron microscopy?SEM? test.Based on the finite element analysis software?Plaxis?,I make numerical simulation analysis when the nano-material-cement soil and the pure cement soil are used as road base materials.The main research results of this paper are as follows:?1?Through the 7d,14d,28d unconfined compressive strength test under three curing ages,I find that adding nano materials can not only improve the early strength of cement soil very well,but can improve the late strength of cement soil.The unconfined compressive strength of nano-SiO₂ cement soil under three ages increases with the increasing of the content of nano-SiO₂.The 7d compressive strength of nano-aluminum-cement-soil increases with the increase of nano Al2O₃ content,but its 14d and 28d compressive strength first increases then decreases with the increase of the dosage of nano Al2O₃.Considering 14d and 28d compressive strength,the mixing amount of nano Al2O₃ has an optimum value,and the optimum value is between 2%?3%.Under the same dosage the ultimate strength of nano-silicon-cement-soil is generally higher than nano- aluminum-cement-soil.?2?The effect of the experiment when nano SiO₂ and nano Al2O₃ are mixed is superior to the effect when they are added alone.But the compressive strength of cement soil will decrease when the added amount of nano material is too much.The compressive strength of nano-material cement soil increases with the growth of the curing age.?3?Through the 7d split test,I find that the adding of nano materials can greatly improve the indirect tensile strength of cement soil.When the added amount is too small or too large,the 7d splitting strength of nano silicon-cement-soil is bigger than nano- aluminum-cement-soil.While the added amount is suitable,the 7d splitting strength of two kinds of nano-material cement soil is very close to each other when they are added alone in same dosage.When the two kinds of nano materials are mixed,the improvement of 7d splitting strength of cement soil is significantly greater than the value when they are added alone.?4?The ratio between 7d splitting strength and 7d compressive strength of nano-material cement soil is between 0.130-0.160,which is bigger than the value of pure cement soil.The ratio ?s/qu will increase with the increase of the adding amount of nano material,and it will be up to its maximum when the two nano materials are mixed.?5?The results of Scanning Electron Microscopy Test shows that adding nano materials will make big pores in cement soil be filled and be refined. Strong volcanic ash reaction will happen between nano materials and cement hydration products,which not only promotes the cement hydration reaction but also generates a large amount of C-S-H and C-A-H flocculation gelling materials.They are filled in the pores or are wrapped around the needle cylindrical Ettringite Crystal,which can make the mesh structure more compact and can enhance the bond between the cement stone frame.?6? Based on the Plaxis finite element analysis software,I make numerical simulation analysis when the nano-material-cement soil and the pure cement soil are used as highway subgrade materials.The results of numerical simulation analysis shows that the strength of highway subgrade will be improved if we add nano SiO₂ and nano Al2O₃ in cement soil.We can use it to improve the road performance of highway subgrade.