Research On Aggregate Contact Characteristics Of Asphalt Mixture During Compaction

As a complex multi-component material,the internal components of asphalt mixture have an important impact on the performance of asphalt mixture.The contact between aggregates in asphalt mixture is the fundamental reason for the formation of asphalt mixture skeleton strength.However,the evaluation indexes of asphalt mixture skeleton strength are mostly volume indexes based on macro characteristics.With the development of CT technology and computer technology,researchers began to use these new technologies to study the internal mesostructure of asphalt mixture,and try to explore its strength formation mechanism.In this paper,specimens with different compaction degress are formed by rotary compactor to simulate a dynamic process of Asphalt Mixture Compaction.Taking the asphalt mixture specimen with the best asphalt aggregate ratio as the standard specimen,the asphalt mixture specimens with compaction degree of 85%,90%,93%,96%and 100%were formed.The micro structure information of the asphalt mixture during compaction was obtained by CT tomography and image processing technology.The conclusions are as follows:Digital image processing technology of asphalt mixture.The traditional Otsu method is improved and a multi-threshold Otsu segmentation method based on ring partition is proposed.The results show that the multi-threshold Otsu segmentation method based on ring partition can segment the aggregate in the digital image of asphalt mixture and has good adaptability.The number of "free particles" in the asphalt mixture has a great relationship with the size of the aggregate.The larger of the aggregate size,the less likely it is to become "free particles".With the progress of compaction,the number of "free particles" decreases,indicating that the number of "free particles" can reflect the skeleton structure strength of asphalt mixture to a certain extent.With the increase of compaction degree,the average coordination number of aggregate will increase,but for 13.2～16mm aggregate,the change of average coordination number will fluctuate in the middle stage of compaction.The frequency distribution curve of coarse aggregate spindle inclination presents Gaussian distribution,and the aggregate spindle inclination is mainly concentrated in the angle range of 65°～115°.With the improvement of the compaction degree of the asphalt mixture,the spindle inclination of the aggregate tends to be more and more in the range of 80°～1 00°,indicating that the aggregate is becoming more and more "horizontal".The greater the degree of compaction of asphalt mixture,the more the number of contact chains.Among them,the number of 9.5～9.5,4.75～4.75,and 4.75～9.5 types of contact chains is the largest,accounting for more than 90%of the total number of contact chains.The number of 4.75～9.5 types of contact chains is the largest among the six types of contact chains,and the growth rate is the fastest.The number of 4.75～4.75 types of contact chains is more,and the growth rate is faster.The change of the number of 9.5～9.5 types of contact chains is relatively stable in the whole compaction process.The total length of the contact chain increases with the increase of compaction degree.However,the total length of the contact chain decreases in the final stage of compaction.It means that during the compaction process,the aggregates will not only contact each other but also the aggregates themselves will adjust the spatial position state to form a more stable skeleton structure.As the degree of compaction increases,the number of contact chains with angles in the interval range of 80° to 120° increases significantly.From the Gaussian distribution,it can be seen that the angular expectation of the contact chains in each compaction stage is concentrated at 93°,indicating that most of the contact chains are in a "horizontal" state.A correlation model between the dynamic modulus and internal fine-scale parameters of the asphalt mixture was developed.The number of contact chains correlated well with the dynamic modulus,with the correlation coefficients above 0.9 at the temperature environments of 35℃ and 50℃.