| Asphalt, with excellent adhesion and viscoelastic properties, is a good paving material for high grade roads and bridge construction. However, with the increasing traffic load, high demand of new lane design as well as the changeable climate conditions, the more superior performance of asphalt is vitally needed. One effective way is to add various modifiers, such as polymer, nano-layered materials and chemical modifying agent into asphalt to obtain the modified asphalt with excellent physical performance, anti-aging and creep resistance, which become a hot pint. Nano-layered material(organic montmorillonite(OMMT), layered double hydroxides(LDHs)) and polymer(crumb rubber(CR), ethylene vinyl acetate(EVA)) were used to modify asphalt. Furthermore, the properties, microstructure and modification mechanism of nanoclay/polymer composite modified asphalt were discussed. The following conclusions are obtained:(1) Nano-layered OMMT and LDHs show different dispersion structures in nano-layered material/polymer/asphalt triple composites, for example, intercalated, exfoliated structure packing-like state. The interaction between asphalt and polymer and comprehensive performance of asphalt can be enhanced effectively by nano-layered material, especially the OMMT. Polymer(CR or EVA) can effectively improve the physical properties, aging resistance and rheogical properties of the modified asphalt, but the mechanisms are different.(2) Compared to the polymer(CR or EVA) modified asphalt, there are an increase in softening point, and a decline in penetration and ductility of the triple asphalt composites with the content of nano-layerd material(LDHs or OMMT) increase, which indicates that the rutting resistance performance of the triple asphalt composites is enhanced, and the nano-layerd material(LDHs or OMMT) has a good hardening effect on the whole polymer modified asphalt.(3) The compatibility between polymer and asphalt is improved obviously by OMMT or LDHs. The different softening point between the bottom and top sections of tubes(ΔSPstorage) in segregation is decreased remarkably(< 2.5 ℃) after incorporation of OMMT or LDHs. The existence of numerous LDHs within nano-layered material/CR compound modified asphalt, prevents the CR particles from accumulating(the mean radius of CR particles becomes small) and minimize the difference in density of the whole triple composites; the formation of network between EVA and asphalt for OMMT, restrain the relative motion within the whole composites. So both the triple asphalt composites show excellent property of stability storage.(4) The thermal oxygen/UV aging resistance of composite modified asphalt is improved with the adding of OMMT or LDHs. During the asphalt aging process, the OMMT or LDHs with high aspect ratio greatly obstruct the permeation of oxygen and the volatilization of asphalt oil components, furthermore, the LDHs can also play a multi chemical absorbability and physical shield effect role in the LDHs/CR compound modified asphalt, which makes the organic material an excellent UV resistant property.(5) The obtained triple composites show an increase in complex modulus(G*), a decrease in phase angle(δ), as well as the TSHRP increase nearly 16 ℃,which mean that the OMMT/EVA compound modified asphalt display a good rutting resistance, high elasticity and superior anti-cracking properties. |
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