Study On The Effect Of Layered Double Metal Hydroxide On Flame Retardancy And Road Performance Of Asphalt

With the development of the national economy,together with the accelerated urbanization process,more and more tunnel asphalt pavements have been applied into building expressways and urban expressways.However,due to the semi-enclosed space of the tunnel,once the fire breaks out in the tunnel,amounts of heat will ignite the asphalt pavement in a short time,which further intensifies the fire and endangers the safety of person and property.Therefore,it is of great significance to conduct research on the tunnel flame retardant asphalt.This research was sponsored by both the“Basic Combustion Law of Asphalt Combustion and Construction of Targeted Flame Retardant System”?51808521?,which belongs to the National Natural Science Foundation of China,and the“Optimization of Flame Retardant Performance Based on Asphalt Composition Characteristics”?LQ17E080011?Funding,which belongs to Zhejiang Natural Science Foundation.First,the matrix asphalt was separated through four-component analysis,and its components were subjected to thermogravimetric analysis.The thermal analysis of the matrix asphalt was carried out by thermogravimetry-differential heat and cone calorimetry.Secondly,four kinds of LDHs were selected to prepare 10wt%of asphalt cement,and the samples were put into tests including characterization,limiting oxygen index and cone calorimeter test,preferably LDHs species.Then,the effects of ZnMgAl-CO₃-LDHs?Z-LDHs?content on the flame retardancy of asphalt were studied by the limiting oxygen index and cone calorimeter tests.The flame retardant mechanism of Z-LDHs was revealed by thermogravimetry-differential heat and residue analysis.Finally,based on the Superpave system,a research was carried out on the effect of high-volume Z-LDHs?25wt%?on such factors as the construction,workability,high temperature performance,anti-aging property and low temperature property of the asphalt.The main findings are as follows:?1?The saturate was of the worst thermal stability of the four components,while the thermal stability of the asphaltenes is the best with the highest percentage of combustion residuals.Besides,the highest level of aromatics contributes the most to the asphalt combustion.The process of matrix asphalt combustion is divided into three main stages,and the maximum weight loss rate of each stage increases in turn.During the third stage,the percentage of mass loss and the mass loss rate reach their maximums.Under radiation conditions caused by medium fire scale of 50 kW·m^-2,the highest heat release rate of matrix asphalt combustion can reach 762 kW·m^-2.?2?The LDHs does not peel off in the asphalt cement with 10wt%LDHs.The crystal phase remains intact within the asphalt,and no asphalt permeates the LDHs layer.Moreover,LDHs can increase the oxygen index of the asphalt,but the addition of 10wt%LDHs improves the oxygen index of asphalt less obviously so that it cannot meet the oxygen index requirement of tunnel flame retardant asphalt.The addition of LDHs can reduce the heat release rate?HRR?and smoke generation rate?SPR?of asphalt combustion,and it is most effective to reduce the peak HRR and peak value of Z-LDHs on asphalt when the amount of LDHs is 10wt%.?3?Adding asphalt cement can meet the oxygen index requirements of tunnel flame retardant asphalt when the Z-LDHs content is 25wt%.When the amount of Z-LDHs is less than 25wt%,the effect of increasing the Z-LDHs on increasing the oxygen index of the asphalt cement shows the tendency of first dropping and then rising,as the addition of Z-LDHs increases,the effect of Z-LDHs on decreasing the peak HRR,the peak SPR and the smoke development amount shows the tendency of first rising,then dropping and rising up again.Increasing the Z-LDHs content shows limited effect on reducing the average HRR reduction of asphalt cement.The low-volume?i.e.2wt%?of Z-LDHs content achieves flame retardant effect on asphalt mainly by improving layered barrier of the Z-LDHs,the integrity of the surface carbon layer,the oxidation resistance,and the compactness of the carbon layer.While the high-volume?i.e.25wt%?of Z-LDHs content runs its flame retardant mechanism for asphalt mainly by the dilution of Z-LDHs,and promoting the integrity and the oxidation resistance of carbon layer.Moreover,larger amounts of Z-LDHs are not helpful for formatting densified carbon layer.What's more,Z-LDHs can not play an obvious role in asphalt Endothermic flame retardancyt.?4?With high-volume of Z-LDHs content,the Brinell Rotational Riscosity of asphalt cement increases,but which still meets the construction requirements;Z-LDHs can improve the rutting factor and complex shear modulus of asphalt cement together with is high temperature performance;it also slows down the increasing of the complex shear modulus,the rutting factor of the asphalt cement,which further improves the aging resistance of the cement;besides,when making sure the resilience energy is still not lower than the matrix asphalt,the effect of promoting the stiffness of the asphalt cement slightly on the frozen damage of the asphalt is basically negligible.