Research On 3D Morphological Characteristics Of Coarse Aggregate Based On Laser Scanning

Coarse aggregate is the main component of asphalt mixture,and its morphological characteristics have a significant impact on the mechanical strength and road performance of asphalt mixture.Indirect methods are often used to evaluate the morphological characteristics of coarse aggregates.They are mainly based on manual measurement,visual recognition and simple tests.They play a certain role in controlling the quality of aggregates,but they can only be used for qualitative evaluation.In this paper,laser scanning is used to collect the three-dimensional point cloud data of aggregate particles,to obtain the complete three-dimensional information of aggregate particles,and to quickly,quantitatively and accurately evaluate the shape,angularity and texture characteristics of the coarse aggregate.Image processing technology was first used to study the two-dimensional morphological characteristics of coarse aggregate.Place the limestone with different angularity evenly on the white desktop,take the picture,use Matlab to perform the initial processing of the images,and use the minimum threshold method to extract the coarse aggregate particles in the graph,then perform the coarse aggregate particle contour extraction,and finally use Image Pro Plus calculates the two-dimensional morphological characteristic index of coarse aggregate.After the study,long and short axis,rectangularity,roundness and other parameters these were selected can better describe the morphological characteristics of coarse aggregate.The rectangularity of limestone coarse aggregate increases with the increase in angularity,and deviates more and more from the rectangular shape,its roundness decreases with the increase in angularity,and deviates round more and more from the circular shape.Its angularity does not change significantly with the increase of the long axis,the curve tends to be flat,and the shape of limestone looks like a circle.Subsequently,laser scanning was used to collect the three-dimensional point cloud data of the coarse aggregate surface to complete the study of the three-dimensional morphological characteristics of the coarse aggregate.Perform data filtering,data registration,data reduction and other operations on the collected data,extract the three-dimensional morphological feature indicators of the coarse aggregate,perform statistical analysis on the probability distribution of the sample,and finally calculate the representative value of each morphological characteristic index.After studying the long axis,middle axis,short axis and their ratio,rectangularity,sphericity and other parameters of the coarse aggregate samples of pebbles,granite,and basalt,it is found that these three types of coarse aggregates are closer to the cubic shape,and the shapes of the pebbles are similar.It is closer to a rectangular body than granite and basalt.The shape of basalt is closer to sphere than pebbles and granite.The particle size of the coarse aggregate is inversely proportional to the complexity of the edge profile and the complexity of the surface texture.The distribution of the same index samples of each particle size in the same batch is generally the same but the specific value will be different.The various indicators of different batches of coarse aggregate are significantly different.The morphological characteristics of different batches of coarse aggregate are also different,and the difference in characteristic value is related to the kind of coarse aggregate.Finally take signal-file coarse aggregate tamping density,the results show that the VCA_DRC from the same stockyard decreases with the increase of the particle size.The VCA_DRC of each particle size in the same stockyard is highly relevant.The overall change trend is the same among different stock yards.In different kinds of rock types,the VCA_DRCof granite and basalt is generally higher than that of pebbles.This result has little to do with the type of rock,and is mainly related to the angularity of the aggregate.The three-dimensional morphological characteristic indexes of coarse aggregates（such as squareness,sphericity,volume change rate,surface area change rate）are nonlinearly related to VCA_DRC,and have a good correlation.