Research On The Preparation And Performance Of Warm-mixed Flame Retardant Asphalt Mixture

With the development of economic, highway construction of the eastern coastal area has been basically completed. The national development strategic is transferring to the midwest of our country, which is a big opportunity to the highway construction development. There are many mountains in the midwest of our country, and the highway tunnel construction has become a trend to cross the mountains. Because of the superior performances, there is more and more asphalt pavement applied of in the highway tunnel. Two difficulties hinder the wide application of asphalt pavement in highway tunnel. Firstly, Asphalt belongs to combustible material, which exists fire hazard in the tunnel. Secondly, hot mix asphalt mixture (HMA) is difficult to be paved in highway tunnel, especially in the big and long tunnel. In view of the two difficulties, the profound research on preparation and performance of warm mixed flame retardant asphalt mixture (WFRMA) will be done in this paper. Prepare an asphalt mixture that is suitable for highway tunnel, which has good flame retardant performance and can pave in lower temperature.The warm mix asphalt additive is zeolite 4A containing crystal water which synthesized from coal fly ash by fusion with sodium hydroxide prior to hydrothermal reaction in laboratory. Composite flame retardant is prepared with mixed flame retardants with a weight ratio of DBDPE/Sb2O3/ATH (3:1:1). Firstly, modify the SBS modified asphalt with self-made warm mix asphalt additive and composite flame retardant, and prepare the asphalt binders. The penetration test, the softening point test and the ductility test for asphalt are done to study the impact of additives and the content of additives on the properties of asphalt. With the increasing content of self-made warm mix asphalt additive and composite flame retardant, the penetration and ductility at low temperature of asphalt decrease, while the penetration index and softening point of asphalt increase. Limit oxygen index and asphalt aging ductility are adopted to determine the content of the composite flame retardant. LOI reaches to 23.7%when 8%composite flame retardants is added, which can meet the requirement of flame retardant modified asphalt for pavement. DSR temperature sweep test is done to study the rheological property of the asphalt binder. The addition of self-made warm mix asphalt additive and composite flame retardant can improve the complex modulus of asphalt binder, reduce the temperature sensitivity of asphalt binder, and improve anti-rutting performance of asphalt binder.Base on the design of hot flame retardant asphalt mixture, and Target of 20℃temperature reduction range is adopted to determine the content of self-made warm mix asphalt additive, and then prepare warm mixed flame retardant asphalt mixture. The pavement performances of the two asphalt mixtures are contrasted and evaluated by the immersion Marshall Stability test, the frost thawing and splitting test, the bending-beam test in low temperature, the Marshall Stability test, the rutting test, and the Four-point bending fatigue test. It can be conclude that the moisture stability of WFMA is the same as that of HMA; the crack resistance stability in low temperature of WFRMA is lower that of HMA, but sill can satisfy the requirements specification; the high temperature stability and fatigue performance of WFRMA was higher than that of HMA.Finally, Marshall Specimen burning test and slab specimen burning test are taken to study the flame retardant performance of the two asphalt mixtures. The results show that the burning test can evaluate the flame retardant performance of asphalt mixture. After burning test, the retained Marshall Stability and freeze-thaw splitting strength have reduced. Dynamic stability and structure depth of the slab have obviously increased. WFRMA has better flame retardant performance than HMA.The asphalt performance test and mixture performance test show that the pavement performance of warm mixed flame retardant asphalt mixture prepared with self-made warm mix asphalt additive and composite flame retardant can meet the requirements of specification, and can be widely used in the highway tunnel.