Study On Properties Of Polyurethane Modified Asphalt

This study is purposed to innovate a green and environment-friended polyurethane additive for asphalt modification.The polyurethane pre-polymer(C-PU)with terminal –NCO group was synthesized with renewable castor oil,liquefied MDI,acetone,phosphoric acid as raw materials.The preparation process of C-PU was determined by the infrared qualitative analysis and changes of different parameters in synthesized process.The modified asphalts with 10~40% content of C-PU were respectively investigated through a optimised preparation process of modified asphalt developed in this study.The classical tests for evaluating the performances of the modified asphalts and the rheological properties were carried out.Their molecular weight distributions were also analyzed.The dispersion behavior of the modified and its compatibility with the matrix asphalt were observed by fluorescence microscope.The modification and aging mechanism of the C-PU modified asphalt were analyzed by infrared spectrum and gel permeation chromatography.The results showed that both the high and low temperature performance of matrix asphalt,especially the high temperature performance,were improved as adding C-PU.C-PU can enhance the resistance of the modified asphalt to deformation and its anti-rutting ability in high temperature via "stiffening" and "bomb" effect.The high temperature grade of modified asphalt were increased with the increasing of C-PU;the stiffness modulus of modified asphalt were less than matrix asphalt,the stiffness modulus become larger and the creep rate become smaller as adding C-PU,which indicate that the low temperature flexibility of modified asphalt was improved.The result of temperature sweep test showed that the high temperature performance of modified asphalt was obvious and the complex shear modulus(G*)increases with the increasing of C-PU in the same temperature.The result of multiple stress repeated creep recovery test shown that the creep recovery rate of modified asphalt were significantly higher than matrix asphalt and creep compliance were less than matrix asphalt,which indicated that C-PU can enhance the resistance to deformation and anti rutting ability;The result of linear amplitude sweep test shown that the anti fatigue performance of modified asphalt improved and it can maintained for a period of time to occur deformation and failure under yield stress level.The classical and rheological experimental results consistently indicated that 30% was the point of phase transition.The performance of the modified asphalt was raised with the increase of the modifier content when the total additive amount was less than 30%.But the comprehensive performance of the asphalt would be decreased when the additive content was more than 30%.Percentage of 30% was the optimal value in this study.The anti-aging peformance and storage stability of C-PU modified asphalt were unfavorable at 163 ℃ with refering to the petroleum pavement asphalt specification.C-PU would be easily reacted with matrix asphalt via a series of curing,self-polymerization and oxidation reactions when it was at high temperature.However,the modifier could be dispersed uniformly in the matrix asphalt and there was no obvious phase interface observed in this uniformed system through fluorescence micrographs.The storage stability of C-PU modified asphalt was optimal at 120~130℃ according to adding Brookfield viscosity versus time curves.The standard Marshall Stability of C-PU modified asphalt mixture could meet the requirement of petroleum asphalt.The stability increased with the increase of the amount of C-PU.The modified mechanism of C-PU modified asphalts included the gradual transition from simple physical blending to chemical modification.The polyurethane pre-polymer molecules terminated with-NCO group can react with water and other active hydrides in asphalts and aggregates at high temperatures,which leaded to the performance improvement of modified asphalt and its mixture.