| Asphalt pavement has the advantages of smooth,short construction period,low noise,convenient maintenance and maintenance,etc.It is the most widely used pavement form with the most superior road performance.But the asphalt pavement is affected by natural factors such as heat,oxygen,light and rain,resulting in aging phenomenon,thus becoming hard and brittle,cracking,loose and other diseases,which seriously restricts the service life of the asphalt pavement.Asphalt aging is a long-term and complex process,the essence of which is the transformation of aroma into gum and gum into asphaltene.Although many scholars have tried to add anti-aging materials to asphalt to delay the aging of asphalt,the current anti-aging materials generally have such technical problems as short action time and material failure.Therefore,inspired by the slow release effect of nanoporous materials,this study proposed a new strategy to delay asphalt aging by using porous calcium carbonate microspheres slow release regenerating agent(mainly aromatic subfractions)to supplement the missing aromatic subfractions during asphalt aging process.Calcium carbonate microspheres with abundant nanoporous channels were prepared by chemical double decomposition reaction.Dynamic shear rheological test was carried out to evaluate the aging resistance of asphalt mortar.Atomic force microscopy was used to study the slow release rule of the regenerator.Finally,the slow release mechanism of the regenerator in porous calcium carbonate microspheres was simulated from the molecular perspective.Through this study,the following conclusions are drawn:(1)The morphology and structure of calcium carbonate is affected by the concentration of polyacrylic acid(PAA)solution and polystyrene sulfonate(PSS)solution.Too low or too high concentration is not conducive to the preparation of porous calcium carbonate microspheres.When the volume ratio of sodium carbonate solution,calcium chloride solution,polyacrylic acid(PAA)solution and polystyrene sulfonate(PSS)solution is 2:2:1: When the dosage ratio of sodium carbonate solution to calcium chloride solution is 1:1,the mass concentration of PAA solution is 3.0 g/L,the mass concentration of PSS solution is 3.6 g/L,the water bath temperature is 80 ℃,the stirring rate is 600 r/min and the reaction time is 1.5 h,The prepared porous calcium carbonate microspheres have uniform particle size,large porosity and good morphology.(2)The porous calcium carbonate microspheres with a mass ratio of 5:1 and asphalt regenerator were mixed into anhydrous ethanol at a water bath temperature of 100℃,the stirring rate was 400 r/min,and the vacuum negative pressure was 0.1MPa.The test results showed that the asphalt regenerator was successfully loaded into the calcium carbonate pore.(3)The dynamic shear rheological test was carried out to evaluate the effect of calcium carbonate microsphere content loaded with regenerator on the deformation resistance of asphalt mortar,and to analyze the effect of slow release of regenerator on the aging resistance of asphalt.The results show that for unaged asphalt,the asphalt mortar has the best deformation resistance when calcium carbonate microspheres loaded with 30% regenerator are added.When asphalt is aged,the deformation resistance of asphalt mortar decreases with the increase of microsphere content,but it is always higher than that of matrix asphalt.At the same time,the addition of supported regeneration agent calcium carbonate microspheres can effectively improve the antiaging property of asphalt,and the greater the dosage,the more obvious the anti-aging effect.(4)The effects of single calcium carbonate microspheres loaded and unloaded with regenerator on Young’s modulus and adhesion of asphalt before and after aging were analyzed by atomic force microscopy.The experimental results show that the asphalt adhesion around the calcium carbonate microspheres increases and Young’s modulus decreases,which is mainly due to the concentration gradient formed by the regenerated agent due to the absence of light components of the asphalt after aging,which diffused slowly to the asphalt matrix around the microspheres,softening the asphalt in the microsphere-asphalt interface area,and thus delaying the asphalt aging process.(5)Molecular models of asphalt,regenerator and porous calcium carbonate were established by Materials Studio software,and interactions among asphalt,regenerator and porous calcium carbonate were analyzed by molecular dynamics method.The results showed that the binding force(Fa)of asphalt on regenerator was greater than that of porous calcium carbonate on regenerator(Fb)in both systems before and after aging.Moreover,the multiple relationship between Fa and Fb is more obvious in the aging asphalt system,that is,the aging asphalt and the regenerator have greater binding energy and stronger attraction ability,and the regenerator can be slowly released from the porous calcium carbonate.Through the above research,it is shown that the innovative idea that porous calcium carbonate microspheres slow release regenerating agent can supplement the missing aromatic group in the aging process of asphalt can delay the aging process of asphalt,so as to improve the aging resistance of asphalt,which provides a new feasible technical scheme for extending the service life of asphalt pavement. |
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