| Semi-flexible composite pavement(SFP)is a new structure based on the idea of"rigid-flexible neutralization",which combines asphalt mixture with cement mortar.It not only solves the shortcomings of poor driving comfort and more joints on rigid pavement,but also avoids the damage of flexible pavement caused by seasonal temperature changes.After nearly decades of development,semi-flexible composite pavement has been more and more recognized and valued by people,and scholars have gradually strengthened the research breadth and depth of this kind of composite pavement.However,after a long time of theoretical research and engineering applications,semi-flexible composite materials applied to the upper structure,although its functionality and comfort have been greatly improved compared with the traditional pavement,but semi-flexible composite upper layer also exists cracking problem,which is caused by the shrinkage of cement mortar,resulting in asphalt mixture and grouting materials can not work well together.At present,research in this area is still scarce.Aiming at the cracking problem of semi flexible composite upper layer,this paper mainly studies the following aspects:(1)Gradation design of parent asphalt mixture is carried out according to key indexes such as void fraction,stability and flow value,gradation composition of SPF-13semi-flexible asphalt mixture with void fraction of 25%is determined according to layer requirement and performance index,and SBS modified asphalt with 0.1%fiber is selected to ensure that cement can be fully poured into asphalt mixture.At the same time,it has good integrity and anti deformation ability;(2)The key reason for cracking of semi-flexible composite pavement is the shrinkage of cement mortar.To solve this problem,the shrinkage deformation of cement mortar is reduced by 59.3%by adding shrinkage reducing agent on the basis of other properties of cement mortar;(3)The pavement performance of SFP-13 semi-flexible asphalt mixture is evaluated and analyzed through a series of laboratory tests,including shear resistance,high and low temperature performance,water stability and shrinkage crack resistance.The results show that the pavement performance of the semi-flexible composite meets the requirements of pavement structure,and the addition of shrinkage reducing agent.The dry shrinkage of 28d decreased by 54.8%,and the shrinkage cracking was well inhibited;(4)In view of the shrinkage and cracking properties of SFP-13 semi-flexible asphalt mixture,this paper not only carries out the macro-shrinkage test on the composite materials according to the previous test methods,but also carries out the experimental analysis on the micro-development of the composite materials through the scanning electron microscope technology.It is found that the 28-day crack development state of the composites with shrinkage reducing agent is obviously smaller than that of the composites without shrinkage reducing agent.The interface bond between asphalt mixture and cement mortar is still relatively complete.It is further verified that shrinkage reducing agent can not only inhibit the shrinkage of cement mortar and composites,but also make them both.Maintain good overall performance;(5)In view of the destructiveness of the splitting strength of SFP-13 semi-flexible asphalt mixture,the ultrasonic testing technology is proposed in this paper.The results show that the splitting strength of SFP-13 mixture has a good fit with the wave velocity,and the correlation coefficient R~2=0.95684.In addition,based on the relationship between ultrasonic wave and splitting strength,the experimental curves of ultrasonic wave propagation velocity and dry shrinkage of cement mortar and SFP-13 mixture were fitted,and the results showed that the dry shrinkage and wave velocity of the two mixtures also had a good fit.The correlation coefficients are R~2=0.93476 and R~2=0.9302 respectively. |
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