Theoretical Investigation On The Action Mechanism Of Warm Mix Asphalt Based On Molecular Dynamics Simulation

With the advancement of technology,warm mix asphalt pavement materials have received more and more attention and use due to their characteristics of lower construction temperatures,resource conservation,and reduced pollution.At present,the most common warm mixing processes include three types:organic viscosity reduction technology,foaming viscosity reduction technology,and surfactant process technology.Among them,the surfactant process technology adds special oil soluble surfactants and uses special processing procedures to make asphalt have good compressive strength,tensile strength,compression resistance,and other characteristics,thereby achieving good asphalt pavement quality.This article is based on the theory of tribology and uses molecular dynamics（MD）simulation to study the adsorption and film-forming behavior of long-chain aliphatic imidazoline warm mix agents on the surface of aggregates.The research results indicate that the HOMO and LUMO of warm mix agent molecules with different carbon chain lengths at the hydrophilic end are mainly delocalized on the imidazoline ring and hydrophilic group of the molecule.As the alkyl carbon chain length of the warm mix agent molecule increases,the trend of spontaneous adsorption on the Si O₂/Calcite surface becomes stronger,and the ability to obtain electrons becomes stronger.The adsorption energy of the warm mix agent molecule on the Si O₂（001）and Calcite（104）surfaces and the cohesion energy of the membrane continue to increase,The mean square displacement and self diffusion coefficient of the warm mixing agent molecules gradually increase,and the molecular diffusivity increases.The adsorption and lubrication behavior of asphalt lubricating film between Si O₂aggregate surfaces was studied by molecular dynamics simulation,and the effects of shear rate,system temperature and molecular structure of IMDL warm mix on its adsorption and lubrication were investigated.The research results indicate that as the shear rate increases,the interfacial shear stress of the matrix asphalt lubricating film increases,and the adsorption energy and self cohesion energy of the asphalt lubricating film on the surface of the aggregate gradually decrease.At the same time,the addition of warm mix agents can improve the interaction between the asphalt and the aggregate interface and enhance the strength of the asphalt film;The shear stress changes on the upper and lower surfaces of the matrix asphalt and warm mix asphalt lubricating films under different shear rates are very small,indicating that the system temperature is not the main factor leading to a decrease in adsorption energy and cohesive energy;Within the shear rate range of 60-80 m/s,at a temperature of 120℃,the adsorption energy of the warm mixed agent with a lipophilic end carbon chain length of 16 is the highest.The cohesion energy increases with the increase of the hydrophilic end chain length.Using experimental methods,the effect of C₁₆ surfactant warm mix agent on the performance of asphalt and asphalt mixtures was studied.The research results indicate that with the use of warm mix agents,the hardening temperature of 70#asphalt is slightly lower,while the hardening temperature of SBS modified asphalt increases with the use of warm mix agents,with a hardening temperature difference of over 10℃.The treatment of 70#base asphalt and SBS modified asphalt with a surface active agent can significantly reduce their reaction to temperature and improve their heat resistance.As the amount of warm mix agent gradually increases,the temperature sensitivity of the complex modulus of 70#matrix asphalt and SBS modified asphalt gradually decreases,the frequency sensitivity gradually increases,and the zero shear viscosity at 60℃gradually decreases.Among them,SBS modified asphalt has better temperature and frequency sensitivity,but increasing the amount of warm mix agent is unfavorable for high-temperature performance.The porosity of the finished warm mix asphalt mixture at high temperatures is not significantly different from that of the hot mix asphalt mixture.If the porosity is lower at low temperatures than that of the hot mix asphalt mixture,the finished warm mix asphalt is beneficial for low-temperature compaction of the asphalt mixture,and the curing time has no significant effect on the porosity of the finished warm mix asphalt mixture.