| The production process of hot mix asphalt mixtures not only consumes a lot of energy,but also emits carbon dioxide and harmful gases,causing a greenhouse effect and endangering health.In order to reduce the mixing and paving temperature of asphalt mixtures and to reduce the negative impact on the environment during the production of asphalt mixtures,warm mix technology has been developed.Warm mix technology mainly includes organic viscosity reduction technology,surface active technology and foaming technology.Surface-active asphalt warm additives are becoming increasingly popular because of their low impact on the asphalt mixture,but they are mostly imported and expensive,and the performance of domestic products varies.Therefore,the development of a surface-active asphalt warm additive can effectively alleviate the environmental problems caused by the production process of hot mix asphalt mixtures,and promote the development of green low-carbon highway construction,with important technical reference significance.In this study,three imidazolines were synthesized by amidation and cyclisation.The surface free energy index was used to screen the three imidazolines,and the screened imidazolines were completed by compounding with sodium dodecyl sulfate to finally develop a new warm additive.Then,the effect of imidazoline on the surface tension of asphalt and its compatibility with asphalt were investigated by molecular dynamics.Finally,the cooling effect of the home-made warm mixtures and the law of influence on the asphalt mixing properties were determined.The main work and conclusions are as follows:（1）The dodecanoic,tetra decanoic and hexadecenoic were selected for the synthesis of imidazoline by amidation and cyclisation with tetraethylene pentamine.The reaction temperature and reaction time of the amidation stage and cyclisation stage were determined from the water output in the amidation stage and the absorbance intensity of imidazoline at235 nm in the cyclisation stage,and the optimum reaction time and reaction temperature were determined:150°C and 240 min in the amidation stage and 240°C and 240 min in the cyclisation stage.The synthesized imidazolines were tested by infrared spectroscopy and the characteristic peaks of imidazolines were clarified.The contact angle test was then used to screen the three imidazolines in terms of their effect on the surface energy of asphalt,using the surface free energy index.It was found that the sixteen imidazolines had the greatest effectiveness in reducing the surface tension of the asphalt.The optimum ratio of 6:4 was determined by compounding cadmium imidazoline and SDS with the surface energy index.Finally,the three main indicators and the Brookfield viscosity test were used to test the effect of home-made warm additive on the performance of asphalt.It was found that the softening point of the asphalt decreased and the needle penetration and ductility increased after the addition of the warm additive,although the changes in the three indicators were small.（2）The interfacial models of the origin asphalt,hexadecyl imidazoline and asphalt and the co-blending models of the three imidazolines and the origin asphalt were developed.The reasonableness of the origin asphalt models was verified by the origin asphalt model density,RDF,solubility parameters and glass transition temperature.The distribution states of the component molecules were then observed for the diffusion and blending models.It was found that the rate of diffusion of the lighter components was faster at the beginning of diffusion in the interfacial model,and the asphaltene molecules diffused faster in the later stages of diffusion.The relative concentration distribution shows that the imidazoline molecules tend to attract aromatic fractions and colloidal aggregates more.In the blending model,the sixteen imidazoline molecules are distributed around the asphalt fraction,enhancing the mobility of the asphalt.The non-polar components of the imidazoline molecules are distributed in the lighter components of the bitumen and the asphaltenes are mostly encapsulated by gums.The surface energy of the three models was calculated.The lowest surface energy of 34.75 m J/m2was obtained for the hexadecyl imidazoline asphalt blending model,which has the strongest ability to reduce the interfacial tension of the matrix asphalt.The solubility parameters of the three imidazolines and asphalt were also calculated.The difference between the solubility parameters of hexadecyl imidazoline and asphalt was the smallest at 2.32（J/m3）1/2,and hexadecyl imidazoline was the most compatible with the matrix asphalt.The interaction energy between the three imidazolines and the asphalt was analyzed,with cetyl imidazolines having the highest interaction energy with the asphalt,so that both have good stability.（3）The test specimens of warm origin asphalt/SBS modified asphalt mixtures were formed by Marshall compaction at different temperatures and the void ratio of the specimens was tested at different temperatures.It was found that the home-made warm mixture could reduce the compaction temperature of the matrix asphalt mixture by 25°C and the temperature reduction of the SBS modified asphalt mixture by 18°C.The warm SBS modified asphalt was then tested by rotary compaction tests and the temperature reduction effect of the homemade warm mixture was found to be 17°C.By testing the high and low temperature and water stability properties of the asphalt mixtures,it was found that the dynamic stability of the warm mixtures was reduced by 6.4%,the residual stability ratio by3.8%by immersion,the freeze-thaw splitting strength ratio by 3.5%and the flexural stiffness model by 3.1%.The home-made warm mixture reduces the high temperature performance of the asphalt mixture,but enhances the water stability and low temperature cracking resistance of the mixture to some extent. |
