Stability And Drying Performance Of Emulsified Asphalt

Cold asphalt technology based on emulsified asphalt is more and more popular because it has the advantages of convenient construction,energy saving and environmental protection,reducing asphalt aging,extending construction season and so on.It is in line with the development concept of green development,saving and intensive,low carbon and environmental protection proposed in the outline of building a transportation power.Among them,micro surfacing is a kind of thin layer emulsified asphalt mixture,which can carry out effective preventive maintenance for pavement,and is widely used because of its economic and environmental benefits.Although emulsified asphalt has many advantages and is used more and more widely,its stability has always been a bottleneck restricting its development.The stability is poor,the emulsion is demulsified quickly,and the asphalt is cemented into blocks,which is not conducive to the transportation and normal construction of emulsified asphalt.At the same time,in engineering application,in order to restore the original bonding performance of asphalt,the emulsified asphalt should be demulsified to form asphalt film and evaporate most of the moisture.If there is more water between the asphalt film and the aggregate,the formed asphalt film is not easy to adhere to the aggregate.Therefore,the residual water content has a great influence on the strength of emulsified asphalt mixture.For the thin layer structure of micro-surface,the drying process of emulsified asphalt determines the strength development and mechanical properties of emulsified asphalt mixture to a great extent,therefore,the study of the drying process of emulsified asphalt is helpful to understand the drying and strength development process of emulsified asphalt materials.For this reason,this thesis selects two kinds of cationic emulsifier An and B for micro-surface,and prepares emulsified asphalt according to the needs of the experiment.The factors affecting the stability and drying process of emulsified asphalt are mainly studied,and its action mechanism is studied.the relationship between the stability of emulsified asphalt and the drying process is analyzed.By measuring the macroscopic and microscopic properties such as storage stability,particle size and Zeta potential of emulsified asphalt,the stabilization mechanism of emulsified asphalt was studied emphatically from the aspect of microstructure,and the effects of kinds of emulsifier,amount of emulsifier,pH value of soap and inorganic stabilizer on the stability of emulsified asphalt were discussed.The results show that with the increase of the amount of emulsifier,the stability of emulsified asphalt becomes better,in which the optimum content of emulsifier A is4.0%and that of emulsifier B is 3.5%.When the pH value of soap solution is greater than 2,the stability of emulsified asphalt decreases gradually with the increase of pH value.For cationic emulsifier An and B,the optimum pH value is 2.Inorganic stabilizer has great influence on the average particle size and Zeta potential of emulsion.For emulsifier B,the best content of Ca Cl₂is 0.5%,and the best content of NH₄Cl is 0.75%.The change trend of 1d storage stability of emulsified asphalt with various influencing factors is closely related to the changing trend of average particle size and Zeta potential,that is,the smaller the 1d storage stability is,the smaller the average particle size is,the larger the Zeta point is,and the more stable the emulsified asphalt is.The analysis shows that the influence of these factors on the stability of emulsified asphalt can be attributed to the change of the structure of electric double layer caused by the change of ions in the emulsion.The drying stages of emulsified asphalt and their corresponding physical significance are revealed through the theory of emulsion drying,and the effects of drying temperature,thickness of emulsified asphalt,type and content of emulsifier and pH value of soap on the drying process of emulsified asphalt are analyzed.The results show that the drying process of emulsified asphalt can be divided into three stages:(1)the first stage with high evaporation rate,(2)the intermediate stage in which the evaporation rate decreases rapidly,and(3)the final stage in which the evaporation rate decreases sharply.The increase of layer thickness and the decrease of drying temperature will greatly prolong the drying time of the emulsion.The maximum particle packing density(?_m)of asphalt droplets is an important factor affecting the drying process,and most of the samples reach the maximum particle density in the second stage of the drying process.A method for calculating?_m is proposed,which is convenient to judge the quality of emulsified asphalt from the point of view of drying.Finally,on the basis of the previous research,the relationship between the stability of emulsified asphalt and evaporation film-forming characteristics is discussed.the results show that the greater the one-day storage stability of emulsified asphalt,the larger the average particle size,the smaller the Zeta potential,the greater the?_Crit and?_m,that is,the more unstable the emulsified asphalt is,the easier it is to demulsify,the more easily the water in the emulsified asphalt particles is separated from the form of water-in-oil molecules and exists in the form of free water,and the more moisture is dried.At the same time,the effect of one-day storage stability of emulsified asphalt on?_Crit and?_m is basically consistent with that of the average particle size of emulsified asphalt on?_Crit and?_m,and is contrary to the effect of Zeta potential of emulsified asphalt on?_Crit and?_m.It can be inferred that the effect of emulsifier content on the drying process of emulsified asphalt is fundamentally realized through the influence on the stability of emulsified asphalt.