Effects and mechanism of atmospheric multi-acidic gases on cement-based concrete linings of vehicle tunnels

In order to analyze the effects of atmospheric multi-acidic gases inside vehicle tunnels on concrete, mass gains and neutralizing depths of concrete specimens in accelerated simulation chambers filled with multi-acidic gases or single acidic gas were measured and analyzed. The results showed that the neutralizing rate of specimen in multi-gases chambers was higher by 9.6–12% than that of in corresponding single carbonation chamber. Then concrete specimen exposed to single SO2 attack exhibited high mass gain and low neutralized depth compared with those exposed to single NO2 or CO2 attack. This should be attributed to the facts that gaseous SO2 diffused into concrete nearly all dissolved in pore solution of concrete while larger ratio of gaseous CO2 or NO2 still exit and diffused in un-saturated pores of concrete. Furthermore the products CaSO4·xH2O by sulphation in concrete made the further diffusion of SO2 more difficult. Thus the concrete sulphation by SO2 mainly was concentrated on the surface of concrete while the neutralizing process of CO2 or NO2 could promote further inside the concrete.