Preparation And Properties Of Bitumen/Inorganic Nanocomposites

Asphalt pavement is prone to be destroyed by forming the rutting, cracks, pot holes and stripping during service process, which affects the service performance and service life of asphalt pavement obviously. Many studies have shown that bitumen aging is one of the principal factors causing the deterioration of bitumen pavements, that is, the thermo-oxidative and photo-oxidative aging of bitumen occur under the influence of heat, oxygen, light and water. Consequently, it is important to improve the aging resistance of bitumen by developing new anti-aging modifiers, which will prolong the service life of asphat pavement. Polymer/inorganic nanomaterials show the special mechanical, thermotic, barrier, optical and electromagnetic properties, which contributes to that the adding of inorganic nanomaterials is the important high performance modification and functionalization method to polymer. The inorganic nanomaterials mainly contain layered silicates (e.g. montmorillonite (Mt), vermiculite, rectorite (REC)) and nanoparticles (e.g. nano-SiO2, nano-TiO2, nano-ZnO). The key point of preparing polymer/inorganic nanomaterials is to improve the interface effect of inorganic nanomaterials and polymer, which can be achieved by organic modification of layered silicates and surface modification of nanoparticles. Recently, more and more attention of the domestic and international researchers has been paid to the bitumen/Mt nanocomposite. It has been showed that physical, rheological and aging resistance of bitumen can be improved obviously with the introduction of Mt. However, there are relative few reseacches about the adding of other nanomaterials into bitumen. The investigation of mechanism between the bitumen and inorganic nanomaterials is significant to improve the aging properties of bitumen, expand the bitumen modifiers and promote the application of nanotechnology in road materials.In this paper, inorganic nanomaterials with different composition and structure were prepared by modifying the layered silicates with intercalated agents and nanoparticles with silane coupling agents, respectively. The effect of inorganic nanomaterials on physical, thermo-oxidative and photo-oxidation aging properties was investigated before and after organic intercalation and surface modification. The chemical and microstructures of bitumen/inorganic nanocomposites before and after aging were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The modification and aging resistance mechanism of bitumen/inorganic nanocomposites also studied. The main results obtained are as follows:(1) The interlayer spacing of three layered silicates (Mt, REC and EVMt) can be increased by cetyltrimethyl ammonium bromide (CTAB) or octadecyl dimethyl benzyl ammonium chloride (ODBA). Compared with Mt and REC, the interlayer spacing of EVMt is easily expanded. The interlayer spacing of EVMt increases with the values between1.69and3.16nm in comparison with Mt and REC modified by the same intercalation agents. The intercalation agents show different aggregation structures in three layered silicates interlayers, for example, lateral-monolayer, vertical structure and lateral-bilayer. The intercalation agents content in layered silicates is mainly dependent on cation-exchange capacity.(2) The microstructures of bitumen/inorganic nanocomposites can be reflected more precisely by combining XRD and dissolving-filtrating method, which avoids the true structures hidden by test error during XRD analysis for bitumen/inorganic nanocomposites. The seperation process of layered silicates was performed as follows: first, bitumen/inorganic nanocomposites were dissolved in trichloroethylene and the layered silicates were filtered from the solution. Then the separated layered silicates were characterized by XRD. The results show that Bitumen/Mt and EVMt nanocomposites form the phase-seperated structure, bitumen/ODBA-Mt, REC and ODBA-REC nanocomposites form the intercalated structure, while the bitumen/ODBAEVMt nanocomposite forms the semi-exfoliated structure.(3) The compatibility between bitumen and Mt as well as REC is improved obviously by organic modification. Under the same content, the difference between the softening point as well as the layered silicates content in the upper and lower sections of the toothpaste tubes is decreased remarkably after organic modification. However, the compatibility between the EVMt and bitumen is not enhanced by organic modification. Compared with unmodified bitumen, the softening point and viscosity of bitumen/layered silicates nanocomposites are increased, while the penetration and ductility (10℃) are changed differently. The softening point and viscosity of bitumen are increased more obviously after Mt modification in comparison with REC and EVMt, moreover, the ductility (10℃) of bitumen is increased after Mt modification, which can be improved after organic modification of Mt. However, the ductility of bitumen is slightly influenced by REC and EVMT.(4) The viscosity aging index and softening point increment of bitumen are decreased, while the retained ductility are increased after thin film oven test (TFOT) and pressure aging vessel (PAV) aging with the adding of Mt, REC and EVMt. Compared with REC and Mt, bitumen/EVMt nanocomposite shows the lower viscosity aging index and softening point increment, and the higher retained ductility. The thermo-oxidative aging resistance of bitumen/EVMt nanocomposite is further improved after EVMt organic modification which shows slightly influence on its ultraviolet (UV) aging properties. The aging resistance of bitumen/EVMt nanocomposite is affected remarkably by the composition and structure of intercalation agents. Bitumen/ODBA-EVMt nanocomposite shows the lower viscosity aging index and mass change ratio in comparison with CTAB-EVMt after TFOT, PAV and long term aging, which can be attributed to that the formation of carbonyl in bitumen is restained as well as the transformation from sol-gel structure to gel structure during thermo-oxidative aging by ODBA-EVMt.(5) After ultraviolet (UV) aging, bitumen/Mt nanocomposite shows the lower viscosity aging index and softening point increment in comparison with unmodified bitumen, while the the UV aging properties of bitumen are slightly influenced by REC and EVMt. According to AFM analysis, bitumen shows the dispersed phase the core of which is asphaltenes and the matrix phase mainly contained light components due to the structure and stiffness diffference in various bitumen molecules. The association reactions of the dispersed phase as well as the hardening of bitumen occur during UV aging. However, the association reactions of the dispersed phase as well as the hardening of bitumen are prevented during UV aging by Mt. Furthermore, the two phases are still obvious in bitumen/ODBA-Mt nanocomposite, and the viscosity aging index and softening point increment are further decreased in comparison with Mt after UV aging, indicating its good UV aging resistance.(6) The silane coupling agents are bound on the surface of the three nanoparticles according to FTIR analysis and ablation tests. The silane coupling agents content in the three nanoparticles is as follows:DB-560-nano-ZnO> DB-560-nano-SiO2>DB-560-nano-TiO2. The compatibility between bitumen and nanoparticles is improved obviously by surface modification. Under the same content, the difference between the softening point as well as the nanoparticles content in the upper and lower sections of the toothpaste tubes is decreased remarkably after surface modification. Nano-ZnO shows the best compatibility with bitumen after surface modification among the three nanoparticles. The penetration and ductility are decreased, while the softening point and viscosity of bitumen are increased with the addition of nanoparticles. However, this effect is weakened after surface modification of nanoparticles and DB-560-nano-ZnO has the most influence.(7) The softening point increment and viscosity aging index of bitumen after UV aging are decreased with the addition of different nanoparticles. Bitumen/nano-ZnO nanocomposite shows the best UV aging resistance. It can be attributed to the different UV-shielding properties of the three nanoparticles. Nano-Si02has stronger reflection effect to ultra violet, while nano-TiO2and ZnO show the strong absorption effect. Compared with nano-TiO2, the absorption effect of ZnO is more obvious. Compared with reflection effect, the UV aging resistance of bitumen is improved more obviously by absorption effect of UV radiation. The UV aging resistance of bitumen/nanoparticle composites is further enhanced by surface modification of nanoparticles, and bitumen/DB-550-nano-ZnO composite shows the best UV aging resistance.(8) The photo-oxidation of bitumen can be prevented remarkably by nano-ZnO before and after its surface modification. The carbonyl indices of bitumen/nano-ZnO and DB-550-nano-ZnO composites are decreased more obviously in comparison with unmodified bitumen under the same UV aging time. However, this effect is weakened with the increasing of UV aging time. The heterogeneous nucleation crystallization of asphaltenes is accelerated by adding the nano-ZnO which also changes the "bee-like" structures as well as its dispersion in bitumen. Compared with unmodified nano-ZnO, the diameter of crystals is decreased obviously and its dispersion in bitumen is more homogeneous in bitumen by DB-550-nano-ZnO. The surface roughness increases and single phase trend caused by components changes in bitumen are prevented with the addition of nano-ZnO during UV aging, which is improved more obviously by DB-550-nano-ZnO, indicating the good UV aging resistance of bitumen/nano-ZnO and DB-550-nano-ZnO composites.