Characterization Of Mechanical Sand Grain Shape Parameters And Their Influence On The Properties Of High-performance Concrete

In recent years,the consumption of sand and gravel aggregate has increased year by year,and natural sand resources have gradually been depleted,with the national "14th Five-Year Plan","carbon peak,carbon neutral" strategy proposed,the status of machine made sand is particularly important.Compared with natural sand,machine sand has a wide range of sources,which can reuse waste rock and waste materials and other waste resources.It can use materials locally,reduce transportation costs,and has excellent use effect in practical projects.However,due to the difference in crushing methods,the quality of machine sand particles is uneven,and the shape of machined sand particles is an important factor affecting the performance of high-performance concrete of machined sand.Therefore,based on digital image processing technology,this thesis characterizes the mechanical sand grain shape of different crushing methods(hammer crushing,jaw crushing),established the evaluation index and standard of machine-made sand grain shape,designs the mechanism sand shape mix ratio on the basis of the mechanism the influence of the mechanism send shape characterization parameters and particle shape function,and analyzes the influence of the mechanism sand shape on the workability and mechanical properties of the high-performance concrete of the machine sand combined with the particle shape evaluation index.The main research contents and conclusions are as follows:(1)Based on digital image processing technology,three geometric characteristics of machine-made sand were analyzed and established: The distribution rules of shape characteristics,angular characteristics and texture characteristics,and the evaluation indexes of grain shape sensitivity of machine-made sand were studied by mathematical statistics analysis method.The results showed that the difference of grain shape of machine-made sand was mainly reflected in shape characteristics and angular characteristics.The spheroid similarity of 0.55 and equivalent ellipse circumference ratio of 1.05 were used as evaluation indexes and standards for shape characteristics and angular characteristics of machine-made sand respectively.(2)On the basis of the shape evaluation index of machine-made sand,combined with the grain shape function and the stripping coefficient theory,the mix design and trial allocation of high-performance concrete with machine-made sand were carried out.At the same time,the influence of grain shape on the workability of high performance concrete with machine-made sand was tested under different water-binder ratio and sand rate.The results show that the mixture design method based on grain shape can effectively design high performance concrete with machine-made sand that meets the requirements and has excellent performance for the machine-made sand under different crushing modes.Under different water-binder ratios and sand rates,the workability of the high performance concrete prepared by jaw sand is better than that of the hammer sand,and the sand rate required to achieve better concrete workability is also lower.There is a good correlation between the evaluation index of machine-made sand grain shape and the workability of concrete.As the shape of machine-made sand particle tends to be spherical and the angularity becomes weaker,the workability of high-performance concrete with machine-made sand also improves.(3)The influence of grain shape on mechanical properties of high performance concrete with mechanical sand was evaluated by means of concrete compressive strength and electrochemical impedance spectroscopy,combined with mercury injection(MIP)and scanning electron microscopy(SEM),and the microscopic mechanism was analyzed.The results show that under different water-binder ratios and different ages,the compressive strength of high-performance concrete with jaw sand is better than that with hammer sand,and the impedance value of concrete with jaw sand > hammer sand > river sand at different ages,and its porosity is also shown as jaw sand(7.03%)< hammer sand(11.53%)< river sand(15.08%).SEM microscopic analysis also shows that the structure density of the sand is jaw sand > hammer sand > river sand.When the larger the spherical similarity(Q)and the lower the equivalent elliptic circumference ratio(CT),the larger the angular evaluation index(Q),the higher the macroscopic performance and microstructure of high-performance concrete with mechanical sand are,the lower the cumulative pore volume,the narrower the pore size distribution and the denser C-S-H gels are generatedIn this thesis,a series of researches are carried out in the aspects of the evaluation method,evaluation index and the influence of the mechanical sand shape on the performance of the mechanical sand high performance concrete,which makes a beneficial exploration for the establishment of the evaluation system of the mechanical sand shape and the influence of the grain shape on the performance of the mechanical sand high performance concrete.