Study On Dispersion Characteristics Of Warm Mix Recycled Bitumen And Asphalt Mixture

When the recycled asphalt pavement(RAP)content exceeds 30%,it will cause problems such as high RAP heating temperature,low discharge temperature,asphalt aging,large energy consumption,environmental pollution,etc.,domestic and foreign experts proposed warm mix recycling technology for these problems,which alleviates these problems to a certain extent and brings economic and environmental benefits,but also brings new problems such as insufficient integration of new and old asphalt,poor dispersion and integration of new asphalt and RAP and uneven dispersion of RAP in the mixture.Starting from the above three aspects,this paper explores the influence of the key processes of warm mix recycled asphalt mixture on the performance of the mixture,and studies the size of the influencing factors and their optimal combination,so as to provide theoretical support for improving the mixing and construction process of warm mix recycled asphalt mixture.Firstly,the 70#matrix bitumen and laboratory RTFOT simulated long-term aging bitumen were fused by self-made fusion molds at 125°C,145°C,165°C and 0.5h and 1.0h time conditions,respectively,and then the diffusion fusion was analyzed by using the sulfoxide functional group index based on Fourier infrared spectroscopy,and the results showed that compared with the first 0.5h,the SI value change amplitude was greatly reduced in the second 0.5h of fusion.The diffusion rate of the difference in concentration of old asphalt is also slowing down,and the diffusion effect of new and old asphalt only exists within a certain range,which is related to the fusion temperature.The linear correlation coefficient R~2 between the square root of the SI change and the fusion temperature at each point can reach 0.9 or even 0.99,indicating that the square root of the SI change is linearly positively correlated with the fusion temperature,and the SI change is linearly positively correlated with the square of the new and old asphalt fusion rate.Secondly,RAP and original asphalt were mixed with and without warm recycler,and then RAP fine aggregate(5-10mm)and coarse aggregate(>10mm)were based on three-dimensional fluorescence spectroscopy 10mm)The results showed that compared with direct mixing,after adding 6%warm mix recycler,the degree of blue migration of the third layer of fine aggregate asphalt was reduced by 41.9%and 39.8%,respectively,indicating that the warm mix recycler could achieve the ideal regeneration effect by adjusting the components of the aging asphalt on the RAP surface during the mixing process,which could greatly improve the dispersion and fusion of new and old asphalt under the warm mix process.Finally,under different levels of old material preheating temperature,new material preheating temperature,mixing temperature and mixing time,the uniformity of RAP position dispersion and the degree of RAP agglomeration are analyzed based on digital image processing technology,and the results show that the mixing time and RAP material preheating temperature have the most significant effect on the dispersion uniformity of RAP material,and appropriately prolonging the mixing time can achieve better dispersion effect,when the preheating temperature is 120°C and the mixing temperature is 135°C.RAP can already achieve a good dispersion uniform effect,on this basis,continue to increase the temperature effect is not good.Under the conditions of the test material and mixing process level,the optimal mixing scheme considered comprehensively is:preheating temperature of old material 120°C+preheating temperature of new material170°C+mixing temperature of 135°C+mixing time 260s.