Study On Performance Of Hot Recycled Asphalt Mixtures Through Microwave Radiation Heating

The hot recycling of reclaimed asphalt pavement(RAP)has been gained increasing concern recently.How to improve the performance of hot recycled asphalt mixtures is one of the critical topics.The heating methods and temperature of RAP are important factors affecting the performance of hot recycled asphalt mixtures.As for the traditional heating methods,the heat transfers from the outside of the RAP to the inside by conduction,which takes a long time(normally hours)and is easy to accelerate the aging process of the RAP.However,microwave heating is a spontaneous heating process of the materials caused by the microwave radiation,which means the heat can transfers from the inside to the outside,resulting in a fast heating rate and homogeneous heating pattern.Consequently,the absorbed asphalt in the RAP can transfer from the inside to the outside of the RAP by microwave heating,and integrate with the new asphalt better,which can lead to the superior performance of recycled asphalt mixtures.In this paper,microwave heating was used for the hot recycling of RAP,and the corresponding performance of recycled asphalt mixtures was investigated.The results can provide an innovative method for hot recycling of RAP.First,the aging grade of the asphalt in the RAP was evaluated.The old asphalt was extracted from the RAP,and the penetration(250C),softening point,viscosity(135?)were investigated.The results showed that the asphalt content in the RAP was 4.28%,and it just presented a slight aging Grade?.Secondly,Marshall Design method was used for the gradation design of the recycled asphalt mixtures with different RAP contents.According to the 30%,40%and 50%of RAP contents,steel-cotton fiber recycled asphalt mixture and carbon black recycled asphalt mixture were designed respectively.The results showed that the optimum asphalt ratio of recycled asphalt mixture decreases with an increase in RAP content.Then,the effect of microwave on the heating performance of different recycled asphalt mixtures was studied.Marshall samples and loose asphalt mixtures were fabricated according to the designed gradations.The temperature fluctuations of all the samples heated by microwave with different radiation time were studied by infrared thermograph.The results showed that under the microwave radiation,RAP content had no evident effect on the heating rate of recycled asphalt mixtures.However,the addition of steel-cotton fiber and carbon black could effectively improve the heating rate of recycled asphalt mixtures.Finally,the effect of microwave heating on the performance of recycled asphalt mixtures was investigated.The water susceptibility,high-temperature stability,fatigue resistance and crack resistance of recycled asphalt mixture were evaluated by Immersion Marshall test,Uniaxial Penetration Strength test,Four-Point Bending Fatigue test and IDEAL Cracking test,respectively.The results showed that compared with the traditional heating methods,the recycled asphalt mixtures heated by microwave exhibited superior performance of all the water susceptibility,high-temperature stability,fatigue resistance,and crack resistance.Moreover,the higher the RAP content was,the more significant improvements in the performance caused by microwave heating could be achieved.