Research On Digital Control And Detection Technology Of Coarse Aggregate Size Of Asphalt Mixture

The size of coarse aggregate particles is the key factor that constitutes the skeleton structure of asphalt mixture,which will affect the effect between asphalt and aggregate particles,thus directly affecting the workability,shear strength,tensile strength,fatigue strength and stiffness of asphalt mixture,and has a significant impact on the road performance of asphalt mixture.Measuring the size of coarse aggregate particles is generally used to judge whether the aggregate is needle-like.Because needle-like aggregate particles are easily crushed,various properties of the mixture will be reduced.At present,the measurement method is vernier caliper method,which is manual measurement.It is influenced by subjective factors and easy to cause errors.Lack of more rapid and convenient and traceable aggregate size data detection means.In this thesis,the surface contour extraction of stacked coarse aggregate particles on the conveyor belt is realized based on digital image processing technology.The influence degree of coarse aggregate size on the performance of various asphalt mixtures was verified,and the fitting ellipse and shape factor were used to judge the particle size and needle content.Analysis of the key factors in image acquisition,design and develop coarse aggregate size control detection system;The sampling standard based on the system is also set.The main research contents and conclusions of this thesis are as follows:(1)Based on digital image processing technology,the coarse aggregate image preprocessing is used to optimize the coarse aggregate contour information.Thresholding and morphology are combined to separate the surface particles of coarse aggregate image.Watershed algorithm was used to segment the adhesive particles and then the secondary area filtering was performed to realize the complete segmentation of the lower particles and the shadow parts.Finally,the contour of coarse aggregate particles is reconstructed by convex hull theory,and the contour of coarse aggregate image surface layer particles is extracted.(2)Test to verify the influence degree of coarse aggregate size on the water stability,high temperature stability and other properties of various asphalt mixtures.The least square method was used to fit the contour of coarse aggregate particles by ellipse,and the size error was compared and analyzed by manual measurement to verify the size integrity of coarse aggregate particles extracted by digital image processing technology.The shape factor was used as the basis of particle shape judgment,combined with the existing detection methods of test and comparative analysis,to verify the shape factor of each particle shape detection accuracy.(3)Through the simulation of conveyor belt with different speeds and the number of surface layer particles recognition statistics,the upper limit of conveyor belt speed and surface layer particles recognition rate function are set to reduce the influence of conveyor belt movement on image acquisition;In order to verify the ability of anti-illumination interference in image acquisition,the size of identified particles was compared and analyzed under different periods of illumination intensity.(4)Based on the GUI user interface platform of MATLAB software,the surface particle contour extraction algorithm and particle size judgment basis were transformed into programming language,and combined with the influencing factors of image acquisition,the digital control and detection system of coarse aggregate size was designed and developed.Through the system and the existing specifications,the sample size of the actual engineering image collection and manual sampling detection results are compared and analyzed,and the image sampling standard is set.