Study On The Viscoelastic Porperties Of Volcanic Ash Modified HMA In Pavement Structure

After nearly 30 years of development,the highway network in our country has established,with the next stage goal of realizing highway's long service life.Utilization of asphalt pavement with semi-rigid base is the characteristic of high grade pavement structures in China.Nowadays,the main distresses of semi-rigid asphalt pavement have become rutting,low temperature cracking and reflection cracks,instead of net-cracking and alligator-cracking induced by water damage in early years.Among the main distresses,the flow rutting occurred in semi-rigid structures is becoming more and more serious.Meantime,there are some engineering phenomena worth of concern.In traditional recognition,rutting deformation that mainly occurs in upper and intermediate asphalt layers has turned to intermediate and bottom layers.The main form of rutting has become the squeeze and heave towards the two sides of the asphalt layer under wheels,instead of the compaction of pavement and deflection.Furthermore,the key impact factor behind the phenomena was the blit-right structure nature of semi-rigid base asphalt pavement.The traditional concept of layer-division was mainly applied in the right structure which adapted flexible base.However,it is different from the causes and characteristics of main early distresses in blit-right structure.Therefore,proposing an effective technical strategy for the blit-right structure to control pavement damage is the prerequisite for realizing a long service life of semi-rigid pavement.First of all,the stress redistribution of blit-right structure was emphatically discussed in this study.It was proposed that the coupling of stress redistribution,high temperature and heavy loading effects was the main reason for the flow rutting of semi-rigid base asphalt pavement.Combining with experiment data of trial roads,the effect of different pavement types on the deformation development of asphalt layers was analyzed.The characteristics of blit-right structures was elucidated,which led the hot-mixed asphalt(HMA)of pavement more prone to behave nonlinearly than that in right structures.This was reflected in the mechanical parameters.A recognition that high-and low-temperature performances of asphalt layers should both be considered for blit-right pavement was obtained.Based on the meso-composition of HMA,the cause of improving the pavement performance of mastic in asphalt mixture was discussed from the perspective of blit-right structures.The difference in the viscoelastic properties between base asphalt and SBS modified asphalt,and its correlation to the high-and low-temperature performance of pavement were systematically analyzed in this study.Meanwhile,the unified evaluation methods on the performance of base asphalt and modified asphalt were explored theoretically.In addition,typical volcanic ashes were selected based on the research project of volcanic ash in Jilin Province to synthesize composite mastics with SBS modified asphalt and base asphalt.The effectiveness of the composite modification on the improvement of the high-and low-temperature performances of asphalt mastics was verified with DSR tests.Furthermore,the micro-mechanism of volcanic ash composite modification was discussed by combining the microstructural testing results of volcanic ash particles.Based on the experimental study of mastics,the high-and low-temperature performances of the modified and unmodified HMA with volcanic ash as fine filler were comprehensively evaluated with the aid of full temperature dynamic modulus tests,low-temperature three-point bending tests and high-temperature penetration tests.It was found from the experiments that volcanic ash can further enhance the modification effect of SBS compared to mineral powder.However,without SBS modified asphalt,the fine filler of volcanic ash cannot improve the performance of asphalt mixture individually.Additionally,the volcanic ash fine filler that has excellent particle properties can assist the SBS to fully perform its modification effect and simultaneously improve the high-and low-temperature properties of HMA.It was indicated by the improvement of ultimate deformation and failure strength of HMA in low temperature condition,the increased modulus and decreased viscous creep of HMA in high temperature condition,and the increased shear strength of the material.Based on composite modification,the strategy to realize long service life of semi-rigid asphalt pavement was discussed.Based on the measurement technique of optical fiber bragg grating,it realized the real time measurement of the longitudinal strain and lateral strain of HMA under dynamic loading at medium to high temperatures.On one hand,the measurement method of complex Poisson's ratio of HMA was explored.On the other hand,through repeat loading-unloading tests,the total strain of HMA was divided into elastic strain,viscoelastic strain and viscoplastic strain,with which the ratio between lateral and longitudinal strain corresponding to each type of deformation was obtained.It was also found that the permanent deformation of HMA was related to the Poisson's ratio of materials.There were apparent differences in the viscoelastic and viscoplastic behaviors between the asphalt mixtures with base asphalt and modified asphalt.In the end,the request of semi-rigid pavement on the performance of asphalt mixture was comprehensively discussed,and the parametric coordination principle of the materials in layer combination design was proposed.