| The number and mileage of road tunnels in China has been increasing significantly in recent years. However, the incidents of the road tunnel due to fire in tunnels ocassionaly occurred which can induce huge problems. Considering the comfortability, maintainience, low nosiy and anti-sliding performance, asphalt pavement is widely adopted in road tunnels. Firing in the tunnel can induce the combustion and pryosis of the asphalt which can emit huge quantity of toxic gases. Fire retardant is a major method to limit the smoke and the damage of the fire in road tunnels. Asphalt includes four components: saturate, aromatic, resin and asphaltene.The thermal behavior of these four components are totally different during combustion and pyrosis. However, the fire retardant of asphalt is designed based on the whole asphalt in the current engineering practice which can not reach optimum fire retarding results.The thermal behavior of these four components were investigated in this study with the finical support of National Science Foundation of China. The products and peak temperatures were recorded to analyze the theromal behavior of the asphalt components. A fire retardant design was proposed based on the results of the theromal behavior of the components which was also verified using lab tests and numerical modeling in this study. This dissertation includes the following contents:(1) The component separation test was conducted based on the Chinese standard"Highway Engineering Asphalt and Asphalt Testing Procedures" to obtain these four components. The mass contents of four components are 11%, 53%, 21% and 15% for saturate,aromatic, resin and asphaltene, respectively. The experience of this test was summarized;(2) TG-MS test was used to analyze the products and temperature change during the combustion of different components. Test results demonstrated that saturate has three peak temperature values; however, other components only have two temperature peaks during combustion. Coats-Redfern Integral Model (CRIM) and Distributed Activation Energy Model(DAEM) were used to calculate the activation energy. The activation energy of saturate and aromatic increased in the process of combustion; on the contrary, those for resin and asphaltene decreased with combustion. Combustion products of different components were also analyzed using mass spectrum method;(3) Pyrolysis tests were also conducted on these four components to analyze the types of products and the peak temperatures. Coats-Redfem Integral Model (CRIM) was used to investigate the theromal behavior of these four components. The products and peak temperatures of these four components during pyrolysis was also compared with those during combustion. The active energies of four compoenents in pyrolysis were lower than those in combustion. The products during pyrolysis were also predicted using mass spectrum method;(4) Based on the results of these four components during combustion and pyrolysis,Al(OH)3 and Mg(OH)2 were selected as the major components of the fire retardant. Covered red phosphorus and expandable graphite have synergetic effect with Al(OH)3 and Mg(OH)2. The concepts of decreasing rate of the weight loss rate and increasing rate of the activation energy were proposed to evaluate the performance of the fire retardant based on the parameters change before and after the including of fire retardant in the asphalt;(5) The performance of these four components with different content of fire retardents at different temperature stage were evaluated using two proposed concepts. A optimum design were proposed based on the lab test results as 48%, 32%, 15%, and 5% by weight for Al(OH)3,Mg(OH)2, covered red phosphorus, and expandable graphite, respectively. A design procedure was proposed based on the test results and a optimum content for different fire retardents was recommended;(6) A commercial software FDS was used to analyze the performance of the proposed combined fire retardant. Temperature and smoke distribution around the firing point were used to demonstrate the effectiveness of the proposed combined fire retardant. |
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