Investigation On Properties And Micro Structuers Of MWCNTs Modified Bitumen

The popularity of nanotechology has provided the new directions for pavement material design and evaluation methods,which allows nanomodifiers and nanoscale micro characterization methods to be widely used in pavement engineering.In this paper,multi-walled carbon nanotubes(GT300,GT350,GT400)with different aspect ratios were investigated.And three kinds of MWCNTs modified bitumen with different dosages(0.5wt%,1.5wt%,2.5wt%of bitumen)were prepared by high-speed shearing method(5000 rpm,180°C,30 minutes).Hence,the storage stability,basic physical properties,temperature sensitivity and high temperature rheological properties were evaluated,and microscopic characterization methods were adopted to investigate the microstructure and ineraction between MWCNTs and bitumen.Finallfy the performance and thermoelectric properties of MWCNTs modified asphalt mixture were evaluated.First,the compatibility of different size and amount of MWCNTs with asphalt were evaluated through the segregation test of polymer modified asphalt,and then the softening point,penetration,ductility and rotational viscosity of modified asphalt.The experimental results showed that the addition of MWCNTs improves the high-temperature performance and viscosity of asphalt,but weakens the deformation ability at low temperature.The main factors affecting the compatibility and physical properties of MWCNTs modified asphalt are the amount and length of MWCNTs.When the modified asphalt is 0.5wt%,the segregation index SI is the smallest in GT300 MWCNTs modified asphalt,while the counterparts of GT400 and GT350(the same length and different radius)were the lowest at 1.5wt%,and they showed the similar trends in physical properties.In addition,the short-thick MWCNTs have a better effect of reducing the temperature sensitivity of bitumen in a high temperature range(>130°C).In the middle temperature region,a small amount(0.5wt%)of MWCNTs indicated no expectation of reducing the temperature sensitivity.Comparing the results of high temperature reological parameters:dynamic modulus,phase angle,rutting factor,non-recoverable creep compliance,and creep recovery rate all indicated that the high temperature performance permanent deformation resistance of both MWCNTs modified asphalts are improved.However,the dynamic shear modulus of slender-type MWCNTs(GT300)did not change with the increase of MWCNTs addition,0.5wt%of this MWCNTs is an optimal content,and the optimal content of short-sized MWCNTs is 1.5wt%.Moveroer,The addition of MWCNTs enhances the nonlinear viscoelastic behavior of asphalt,and is positively related to the MWCNTs content and the aspect ratio of MWCNTs.Secondly,according to the results of X-ray diffraction and Raman spectroscopy,no new substance were found in the XRD pattern,indicating that no chemical reaction occurred after mixing MWCNTs with asphalt.The modification mechanism is only physical blending.The interlayer spacing of MWCNTs/asphalt composites(asphaltene and MWCNTs graphite atom layers)increases with the increase of MWCNTs content,proving enhancement of the interaction between MWCNTs and asphalt.In addition,by comparing the changes of the Raman characteristic peaks of the two modified asphalts,it was found that the strength of the D and G modes of GT400 modified asphalt increases linearly with the amount of MWCNTs,and the linear dependence of GT300 modified asphalt is poor.This results demostreted that the dispersion of GT400MWCNTs in asphalt is more uniform than GT300.When the amount of MWCNTs was more than 1.5wt%,the disorder of MWCNTs was enhanced(I_D/I_G increased),indicating that excessive MWCNTs could not combine well with asphalt,but tend to intertwine and agglomerate.Finally,based on the conclusion of MWCNTs modified asphalt,1.5wt%GT400MWCNTs modified bitumen was selected.Under the same asphalt content and gradation type,the ordinary asphalt mixture and MWCNTs modified asphalt mixture were compared in road performance and thermoelectric performance.The conclusion of the improvement of the high temperature performance of MWCNTs modified asphalt is verified,and there is no obvious difference in the low temperature crack resistance of the two asphalt mixtures.In addition,the thermo-electromotive force of MWCNTs modified bituminous mixture only has a slight increase,while the thermal conductivity is significantly enhanced.