Research On Application Of Flame Retardant Warm-mixed Asphalt Mixture In Tunnel Pavement

With the large-scale construction of large highway tunnels and the river-crossing or sea-crossing tunnels, asphalt pavement is becoming the main trend because of its good skid resistance, smoothness, and noise-reducing perfomance compared with rigid pavement. Considering the flammability of asphalt binder, fire-retardant treatment have to be done with the asphalt material. For the closed construction enviiorment in tunnels, the flame-retardant WMA with the appliction of fire-retardant and viscosity-reducing technology is applicable.The approach that adding the flame-retardant agent and the warm mix additive to asphalt binder to reduce the flammability and the construction temperature of asphalt mixtue is used here. Three representative kinds of warm mix additive, flame-retardant agent and asphalt common used in project are choosed respectively. The orthogonal test design method is used to arrange the tests. The indexes including limiting oxygen index(LOI), penetration, softenning point, low-temperatue ductility and brookfield viscosity are tested and evaluated through the basic analysis and orthogonal analysis. The influence law of the type and content of warm mix additive and asphalt type is comprehensive studied.It is shown that FR1has the best flame resistance among the flame-retardant agents choosed by the orthogonal analysis of LOI. The LOI nearly increase linearly as the content of flame retardant ranges from4%to8%. The addition of flame retardant can reduce25℃-penetration and increase the softenning point of asphalt binder. At the same time FR1can improve the temperature sensitivity of the binder. The three types of flame retardant can decrease the low-temperatue ductility. Condering the flame resistance combined other pavement performance of the asphalt, FR1is selected and the content is of4%asphalt content.It is shown that the warm mixed addive choosed can improve the high-temperature performance. W1and W2referred in the text causes a decrease to the penetration index and the low-temperatue ductility, but the asphalt added with W3has a greater needle-penetration at defferent temperature compared to the puer asphat binder and the ductility index of which is almost the same with the pure binder. For better low-tem perature performance warm mix additve of W3is a good choice. At the same time according to the analysis of the Brookfield visocity of different temperature, it is found that the W3has the best vicosity-reducing ability, and the content of3%asphalt content is appropriate and economical.Two kinds of flame-retardant warm-mix asphalt binder sample prepared with the selceted kinds of additive and the determined content are applied in test of LOI, pavement performance tests and test of DSR. The LOI of asphalt binder mixed with two kinds of additive are both arounding25and which is20%more than the pure asphalt binder. The addition of two kinds of additive cause a reduction to the needle-penentration and5℃ductility, but cause a increasement to the PI and softening point. In the test of DSR asphalt binders mixed with two kinds of additive have a bigger|G*|,|G*|/sinδ and a smaller8. The comprehensive analysis about the indexes tested show that the two kind of additive could improve the high-temperature performance, on the other hand the additve could lower the low-temperature performance.The mix design of AC-13flame-retardant WMA used in engineering is done, the appropriate mineral aggregate gradation and optimum asphalt content is determined. Marshall specimens of flame-retardant WMA prepared at different mixing and compac tion temperatures are tested and the the construction temperature fixed on the principle of same volume-parameter drops by20℃compared with the HMA. The performance of test specimens with determined mix proportion prepared at the decided mixing and compaction temperature can meet the requirements in the specification.Three types of mixtures of the same gradation and asphalt content including HMA prepared with pure asphalt binder, WMA and the flame-retardant WMA are tested in the low-temperature bending creep test. Datas got in creep tests are fitted nonlinearly according to the form of Burgers model. Caculation and analysis are done by the relation between the parameters in Burgers model and the indexes ralated to the low-temperature. It is found that the use of flame-retardant agent and warm-mix additive can lower the the low-temperature performance. It is also verified that there is a good correlation between m-value and index of m/S, relaxation time, dissipative energy ratio.