Research On Cracking Performance Of Asphalt Mixture Reinforced By Fibers Based On Digital Image Speckle Technology

Cracking causes early damage and frequent maintenance of asphalt pavement,which has become one of the main distresses of asphalt pavement in China.Adding fiber is an effective way to improve the crack resistance of asphalt pavement.Fiber mainly plays the role of bridging and reinforcing in asphalt mixture,so as to alleviate the expansion of cracks.The existing research mainly focuses on evaluating the macro cracking performance of fiber asphalt mixture through different types of indoor cracking tests.There is a lack of research on the cracking process of mixture,and it is difficult to quantitatively characterize the synergistic mechanism and crack prevention mechanism of fiber asphalt mixture.Based on the semicircular bending tensile test（SCB）and the digital image speckle technique（DIC）,this study studies the influence of different types of fibers on the cracking performance and process of asphalt mixture,and comprehensively analyzes the cracking behavior of asphalt mixture by considering mineral aggregate gradation,test conditions and other factors at the same time.Firstly,the Marshall test design method is adopted to carry out the mix proportion design and road performance test of AC-13 and AC-20 asphalt mixtures respectively,and the mix proportion design of asphalt mortar is carried out according to AC-13 mineral aggregate gradation,aggregate specific surface area and asphalt film thickness.The results show that the road performance of asphalt mixture meets the specification requirements.After adding fiber,the optimal asphalt aggregate ratio of asphalt mixture increases,and the increasing extent of basalt fiber and glass fiber is slightly lower than that of polyester fiber.Secondly,the principle,standardized processing flow and point selection basis of digital image speckle technology are clarified.The feasibility and accuracy of the analysis method of digital image speckle technology based on VIC-2D are verified by analyzing the loading rate error,controlling the histogram,editing the initial estimation and removing the unloaded image.Then,the semi-circular bending tensile test（SCB）of different types of AC-13 fiber asphalt mixture is carried out,and the digital image speckle technology is simultaneously used to analyze and explore the crack development law of fiber asphalt mixture.The results show that the addition of fiber can effectively improve the fracture energy and flexibility index of asphalt mixture,the enhancing effect is basalt fiber（BF）>glass fiber（GF）>polyester fiber（PF）.According to the time axis of the loading process,the cracking process can be divided into stable development,rapid development and failure stages.The addition of fiber can effectively alleviate the crack growth rate,and prolong the stable development duration of cracks by 1.72s,1.32s and 0.76s respectively,and the flexibility index is directly proportional to the time of stable crack development and inversely proportional to the acceleration speed.Finally,the effect of maximum nominal particle size,asphalt mortar,loading rate and test temperature on the cracking performance and cracking path of fiber asphalt mixture are studied.The results show that the maximum nominal particle size and the strength of asphalt mortar have a great barrier effect on crack propagation.The decrease of loading rate reduces the crack resistance of the mixture,and the decrease of temperature improves the strength of asphalt mortar,weakens the obstacle effect of fine aggregate and reduces the fluctuation times in the rapid development stage of cracks.After adding fiber,the cracking path of asphalt mixture and asphalt mortar becomes more tortuous.The research results provide scientific basis for guiding the application of fiber asphalt mixture,and are of great significance to improve the crack resistance of asphalt pavement and prolong its service life.