Research On Composite Hydroxide Asphalt Flame-retarding System And Pavement Performance

With the improvement of road grades and the development of expressways in China, asphalt pavement was constructed widely in road tunnels because of its excellent pavement performances like driving comforts skid resistance, et al. Due to the flammability of asphalt and the dangers of tunnel fire, the research of flame retardant asphalt and asphalt mixture has drawn great attentions at home and abroad.This research is funded by the National Natural Science Foundation of China "Research on pyrolysis and combustion characteristics of asphalt under fire conditions and nano-clay/metal hydroxides composite flame-retardant system"(No.51408542), the Zhejiang Provincial Natural Science Foundation "Research on pyrolysis and combustion characteristics of asphalt under oxygen-depleted environments with high heating rates and the mechanism of flame retardancy and smoke suppression"(No. LY14E080014). First of all, through a review on the different hydroxide pyrolysis characteristics and flame retardant mechanism analysis, this paper studied the feasibility of metal hydroxide compound. Then, the limiting oxygen index test(LOI)^thermogravimetry and differential scanning calorimetry (TG-DSC) and cone calorimeter test (CCT) were used to evaluate the flame retardancy of asphalt. Finally, The influences of composite hydroxide on pavement performance of asphalt mixture, including high and low temperature performances, fatigue performance and water stability, were studied and the mixing process of flame retardant and economic applicability of composite hydroxide flame-retardant were analyzed.The results show that:(1) Aluminum hydroxide (ATH) and calcium hydroxide (HL) have different temperature ranges on flame retardant effect and different flame retardant mechanisms. The composite flame retardant compounded by ATH and HL can play a role of synergistic flame retardant in a wider temperature range.(2) When the proportion of the composite flame retardant compounded by ATH and HL (1:1) is25%, the limiting oxygen index is24.4%; The composite flame retardant asphalt can improve the flame retardant performance of asphalt mixture that can effectively prolong the time to ignition, reduce the CO production rate and heat release rate of asphalt mixture, compared with adding a single flame retardant. It shows obvious synergistic flame retardant effect.(3) Replacing part of the mineral powder with composite flame retardant by dry-mix is feasible. It not only overcomes the shortcomings that the large amount additive of inorganic flame retardant by using wet-mix will deteriorate the pavement performance of asphalt mixture, but also shows a good economic applicability.(4) The composite hydroxide has good engineering applicability. It can improve the high and low temperature performance, fatigue performance and water stability of asphalt mixture, and overcomes the shortcomings that some performance will be reduced by adding aluminum hydroxide alone. In summary, the composite flame retardant compounded by aluminum hydroxide and calcium hydroxide has good effects on both of the flame retardancy and the pavement performance, even more it is more economical and has a broad application prospect.