Study On Flame Retardant And Smoke Suppression Technology Of Thermal Decomposition Of Asphalt Pavement Under Large Urban Tunnel Fire

With the improvement of urbanization level and the rapid development of urban construction, as an important part of urban traffic system, urban tunnel has been widely used in urban construction. And the trends for long tunnel, the increase of traffic volume and improvement of traffic speed, urban tunnel becomes traffic accident prone locations, which caused the rate of fire accidents is raising. Asphalt pavement is widely used in tunnels due to its advantages: driving comfort, low noise, good skid resistance, short construction period, convenience of maintenance, etc. However, the temperature of the tunnel can rise sharply in very short time if a fire breaks out, a lot of heat flow and toxic fumes are produced due to the thermal decomposition of the asphalt pavement, hinder the trapped personnel to escape, bring great difficulty to the fire rescue work of firefighters, it may be cause huge losses in the end. Therefore, in order to improve the fire safety of the tunnel, it is important to study on flame retardant and smoke suppression technology of thermal decomposition of asphalt pavement.First of all, TG-DSC technique was used to study the asphalt components distribution characteristics of different stages of combustion temperature range in this study, and the initial thermal decomposition temperature, the maximum thermal weight loss decomposition temperature, the thermal weight loss rate and enthalpy change of the four components were analyzed. There are two major weight loss phases in the combustion process of each component of asphalt binder, that is, the thermal decomposition and combustion reaction phase of each component and the oxidation combustion reaction of carbon. The combustion dynamic models of asphalt components were established respectively, and the kinetic parameters of asphalt components in different combustion stages were calculated to analyze the combustion process of asphalt components. The gaseous volatiles released from asphalt components in their different stages of combustion process were studied by TG-FTIR technique, and the components and contents of the gaseous volatiles were detected. The FESEM and EDS methods were adopted to observe the microscopic morphology characteristics and elemental composition of the surface of combustion residues of asphalt components, and the combustion mechanism of asphalt components were studied, which provided theoretical basis for further revealing combustion mechanism of asphalt binder.Secondly, according to the asphalt components gradient distribution characteristics of different stages of combustion temperature range,the environment-friendly flame retardants were selected to match the combustion characteristics of asphalt components. The effects of combustion characteristics of asphalt components by adding environment-friendly flame retardants were investigated through TG-DSC technology and the test results demonstrated that the initial decomposition temperature of each component in the combustion process, the maximum thermal decomposition temperature and residual carbon quality were obviously different. However, the weight loss stages of asphalt components are not changed, divided into two main weight loss stages still. The combustion characteristics of the components of flame-retardant asphalt were studied by used TG-FTIR technique?FESEM and EDS methods, the components and contents of the gaseous volatiles were detected, and the microscopic morphology characteristics and elemental composition of the surface of combustion residues were analyzed. The effect of environment-friendly flame retardants on the combustion performance of asphalt components was studied, which provided the reference for revealing the effect of the compound flame retardants on the flame-retarded mechanism of asphalt components.On top of this, the multi-stages of TG of asphalt combustion was analysed by the point of view of the gradient distribution of asphalt components combustion. The combustion properties of asphalt binder was researched fully, and further revealed the nature of asphalt combustion. According to the research results of the combustion mechanism of asphalt binder, the contents of asphalt components, and the test results of the environment-friendly flame retardants selected to match the combustion characteristics of asphalt components, a kind of multi-component flame retardant which is adapted to the multi-stages combustion behavior of asphalt binder is developed. The effects of combustion characteristics of asphalt binder by adding multi-component flame retardant were investigated through TG-DSC-FTIR technology, FESEM and EDS methods. The synergy between the different flame retardants was discussed, the mechanism of flame retardancy on asphalt binder was analyzed. The test results showed that the flame retardant modified asphalt components have good flame retardant properties, which has important guiding role in the whole flame-resisant process of asphalt thermal decomposition.Finally, flame retardant modified asphalt and its mixture need not only certain flame retardancy and smoke suppression, but also good service performance. The effects of multi-component flame retardant on asphalt and its mixture properties were studied by using the conventional experiments, Brookfield viscosity experiment,DSR experiment, BBR experiment of asphalt binder, and the rutting test, bending creep at low temperature and freeze-thaw splitting tensile test of its mixture. The results showed that the composite flame retardant modified asphalt and its mixture have good road service performance. Based on the experiment results, the multi-component flame-retarded asphalt formulation is recommended, which provides scientific basis for improving the large urban asphalt pavement in tunnel fire safety.