Study On Adsorption And Degradation Of The Tunnel Automobile Exhaust In Road Tunnel Based On The Asphalt Pavement Carrier

As the development of national economy in China and continuously improvement of tunnel construction level, the number of large road tunnels and urban underground passages was increased more and more. Since a tunnel was a semi-closed tubular structure, where ventilation was poor and vehicle speed is low, it resulted that the automobile exhaust concentration in the tunnel was obviously higher than out of it. Thus, it caused serious air pollution, and harmed the health of drivers and passengers. Currently, ventilation equipment and other physical methods were adopted to eliminate and dilute automobile exhaust, but it was difficult to achieve substantial degradation effect of chemical methods. This paper researched and developed a kind of catalytic composite material which is applicable to asphalt pavement and adaptable to tunnel lighting environmental conditions. The asphalt pavement was endowed with functions of absorption and automobile exhaust degradation. It may have significant meaning to improve the air quality in the tunnels and near the exits.Firstly, this paper analyzed the distribution rules of automobile exhaust concentration in the tunnel under different driving conditions on the basis of hydrodynamics theories, and mainly focused on the gradient distribution rules of automobile exhaust concentration near the road surface to provide theoretical basis for asphalt pavement which had photocatalysis function. The calculation results indicated that the automobile exhaust was spread from the road surface to the surrounding in a short time under idling or driving conditions, especially to the both sides of the tunnel. It provided superior conditions for automobile exhaust adsorption and degradation which took asphalt pavement as the carrier.Secondly, this paper used sol-gel method to prepare Fe³⁺ doping with nano TiO₂ and characterized the photocatalyst apparent morphology, surface chemical composition, electronic band structure and optical properties with different Fe³⁺ doping. The results indicated that Fe³⁺ doping reduced the Fermi level of TiO₂ and narrowed the optical band gap. The absorption band edge appeared obvious red shift, and visible light absorption was enhanced significantly. Meanwhile, Fe³⁺ doping resulted in TiO₂ lattice distortion and formed trap to capture photo electron. It reduced the electron-hole pairs recombination rate, accelerated interface transfer reaction of holes and electrons, and improved the photocatalytic performance of TiO₂. Furthermore, researched and developed automobile exhaust purification test system was used to study the degradation effect of TiO₂ with different Fe³⁺ doping to the automobile exhaust, and appropriate Fe³⁺ doping was confirmed.Thirdly, coconut shell AC was used as absorption carrier to prepare AC/ TiO₂ composite photo catalyst on the basis of Sol-gel loaded nano-TiO₂. Scanning electron microscopy, energy dispersive spectroscopy, BET specific surface area and pore size distribution analyzer were used to study the apparent morphology, activated carbon pores distribution and adsorption performance of photocatalytic composite material with different loading times. The results indicates that surface functional groups and unique pore structure of activated carbon improved the surface contaminant concentration of nano TiO₂, played the synergistic effect of absorption performance of activated carbon and photocatalytic performance of nano TiO₂ fully, and improved the photocatalytic degradation efficiency, so that the activated carbon pores could be taken in-situ regeneration. With automobile exhaust degradation test and with combination of characterization analysis results, the appropriate times and load rate of activated carbon loaded nano TiO₂ were confirmed.Finally, the AC/TiO₂ composite photo catalyst was taken as fine aggregate and added in the OGFC asphalt to prepare mixed type photocatalytic asphalt road test specimen and take exhaust degradation and road performance tests and studies. The results indicated that the photocatalytic degradation efficiency was improved along with the increased doping of composite photo catalyst, and composite photo catalyst with different doping had no impact on the road performances of asphalt basically. For comparison study, different doping of nano TiO₂ was added in the cement slurry and poured into the pores of OGFC asphalt mixture specimen to prepare photocatalytic and semi-flexible road test specimen. The study results indicated that cement slurry loaded TiO₂ improved the photocatalytic performance and road performance of semi-flexible road surface, and photocatalyst had better feasibility when it was applied in semi-flexible road surface. The study results may provide new ideas and theoretical for asphalt road carrier to absorb and degrade automobile exhaust, purify traffic environment of the tunnel and reduce the hazards of automobile exhaust to the health of drivers and passengers.