Research On Measurement Method And Experimental Comparison Of Coarse Aggregate Angularity And Surface Texture

Coarse aggregate void content is the core index that affects the strength of asphalt concrete.Related research shows that void content directly affects the compressive strength of asphalt concrete.The change of coarse aggregate morphology will cause its void content to fluctuate,which will directly affect the slurry required to fill the void,and eventually cause the workability of the concrete mixture to change.At present,the coarse aggregate void content is mainly measured according to the JTG E42-2005 standard in the project,but measuring the void content according to the standard is time-consuming and laborious,and it is impossible to achieve rapid measurement.According to the standard ASTM C1252,it can be known that the void content is mainly affected by the morphology of the aggregate.Therefore,researching and finding the most suitable method for characterizing the morphology is of great significance for the rapid prediction of the void content.In this paper,the method of measuring the angularity and surface texture of coarse aggregates is thoroughly studied through the Los Angeles abrasion experiment and void content experiment,and proposed a new three dimensional(3D)angularity index of the fitted ellipsoid method.Experiments are carried out on three 3D angularity characterization methods and three 3D measurement surface texture characterization methods proposed in this paper.The results show that the fitted ellipsoid method is the most suitable method to characterize 3D angularity;the Z-plane volume difference method is the most suitable method for characterizing 3D surface texture.Although 3D characterization has high accuracy,fast and batch detection cannot be achieved in engineering.Therefore,a self-developed high efficiency measurement platform for coarse aggregate morphology is developed in this paper,and derived a two dimensional(2D)angularity index of the fitted ellipse method to eliminate the effect of the macro size of coarse aggregate through mathematical formula.Experimental comparisons of three 2D angularity characterization methods and three2 D measurement surface texture characterization methods proposed in this paper.Theresults show that the fitting ellipse method can effectively eliminate the influence of the coarse aggregate particle size and flat and elongated ratio on the angularity,thereby improving the measurement accuracy of the 2D angularity index of the coarse aggregate;using a linear contour scanner can improve the accuracy of the angularity index measurement of the fitted ellipse method,and the fitting ellipse method is the most suitable method to characterize the 2D angularity;the convexity method is the most suitable method to characterize the 2D measurement surface texture.Further experimental comparison studies of the 2D and 3D morphological characterization methods show that: the angularity index of the fitted ellipse method can effectively characterize the angularity of coarse aggregates;the surface texture index of the convexity method can effectively characterize the surface texture of coarse aggregates.The purpose of studying the morphological characteristics of aggregates is to study the void content of aggregates.Therefore,this paper first constructs abnormal shape aggregate particles by discrete element simulation software,and carry out a lot of natural stacking void content simulation experiments.Second,the morphological characterization method based on image processing technology is used to measure the morphological parameters of aggregates in the filled container.Finally,the measurement results of the morphological parameters are used as the input of the neural network model.After sample training,a fast prediction model of natural stacked void content based on aggregate morphology was established,and the prediction error was within 1%.The work of this paper is helpful for the further investigation of the angularity and surface texture characterization of coarse aggregates and the rapid prediction of void content through the parameters of particle size and shape,it is of preferably theoretical research value and practical value.