Measurement Method And System Development Of Coarse Aggregate Gradation Based On Dynamic Image Method

The particle-size distributions and morphological characteristics of coarse aggregate have an important influence on the quality of concrete.Only by ensuring that the morphological quality of the coarse aggregate conform to national or industry standards,can high-performance and high-quality concrete be obtained.At present,coarse aggregates are measured by the vibration-screening method in engineering,but this method is time consuming and energy consuming,and it can only measure the particle-size distributions of coarse aggregate but not the morphological characteristics of coarse aggregate at the same time.In order to achieve efficient and precise measurement of coarse aggregate morphological quality,the method and system for measuring the morphological quality of coarse aggregate based on the dynamic image method are proposed in the paper to measure the particle-size distributions and morphological characteristics of coarse aggregate simultaneously.Aiming at the shortcomings of the lack of height information in the two-dimensional image method,an integrated measurement system for coarse aggregate morphology and quality based on the three-dimensional image method is designed and developed,and relevant algorithms are studied and designed.The hardware part of the system has designed vibration dispersion module,transmission and laser scanning module,image acquisition module and recycling module.The vibrating feeder,belt,laser,industrial camera,lens,and light source are designed and selected in detail.The software part of the system has designed the image processing algorithm based on OpenCV library,which mainly includes five parts: image preprocessing,feature extraction,color segmentation,particle matching,and calibration.A characterization method of coarse aggregate morphology is designed,which mainly includes five parts: height,particle shape,volume,particle size and particle-size distributions.Based on MFC,a man-machine interface for coarse aggregate morphology quality measurement is designed.The calculation model of coarse aggregate height based on the principle of laser triangulation is verified,and the experiment proves that the absolute value of errorbetween this method and the vernier caliper is within 4%.Based on the four particle shape characterization parameters of elongated ratio,triangularity,flatness and sphericity,the coarse aggregate is divided into six categories: slender,flat,triangular,spherical,slender triangle and irregular.Based on the experimental results of particle shape classification,a new particle size and volume characterization method is proposed.The experiment proves that the new particle size and volume characterization method proposed in the paper is closest to the vibration-screening method.According to the analysis and research on the causes of the errors between image method and vibration-screening method,a particle size correction method based on three-dimensional particle shape and a particle-size distributions correction method aiming at particle-size distributions cross phenomenon are proposed respectively.Experiments prove that the correction method proposed in the paper can effectively reduce the errors between image method and vibration-screening method,making the measurement results of image method closer to vibration-screening method.The repeatability accuracy,particle-size distributions measurement accuracy and measurement efficiency of the independently developed measurement system are tested.The experiments are carried out with single-stage material and grade ingredients of coarse aggregate with particle size ranging from 4.75 to 26.5 mm.The results show that the maximum repeatability errors of single-stage material and grade ingredients are 3.28% and 1.97% respectively.For granite and limestone grade ingredients,the maximum errors of the three-dimensional image method and the vibration-screening method proposed in the paper are within 3% and 4% respectively in each granularity interval.The measuring time for single-stage materials and grade ingredients with a mass of 5Kg is about 6?15min and 10 min respectively.The developed integrated measurement system of coarse aggregate morphology quality can meet the actual engineering requirements and realize rapid and precise measurement of coarse aggregate morphology quality.