Characterization Of Machine-made Sand Particle Morphology And Its Characteristics On The Performance Of Cement Concrete

At present,Guangxi’s control over sand and gravel aggregate mines and river sand mining is becoming increasingly tight.A strict environmental protection implementation plan has been issued,clearly proposing strict control over river sand mining.The contradiction between supply and demand of engineering sand is becoming increasingly prominent,leading to the increasing price of sand and affecting infrastructure construction.In response to a series of issues such as the imminent depletion of natural sand and stone resources,limited mining,and prominent supply-demand contradictions,it is inevitable to replace natural sand and stone with machine-made sand and stone.However,the mechanism sand lacks a professional production design concept,the production process is relatively backward,and the sand and gravel processing equipment does not consider the characteristics of the parent rock.The morphology of the mechanism sand particles is poor,with multiple edges and corners,and there are many needle like particles.The evaluation of the mechanism sand particle shape mostly stays in the two-dimensional direction,and the distribution of grading is unreasonable.For this reason,this paper selects three kinds of fine aggregates with different machine-made sand grain shapes(high-quality limestone A machine-made sand,ordinary limestone B machine-made sand)of different lithology(granite,basalt and limestone),proposes a three-dimensional morphology characterization method that accurately and intuitively represents the morphology of machine-made sand particles,explores the impact of crushing equipment on the limestone grain size morphology,and conducts research on the Methylene blue value of stone powder,Explored the influence of four types of mechanical sand properties on the rheological parameters of mortar and concrete.The main research content and conclusions of this article are as follows:(1)Using the 3D scanner,a three-dimensional scanning technology is proposed to quantitatively characterize the three-dimensional morphology of fine aggregate particles.By combining traditional digital image processing techniques,a comprehensive evaluation of the morphology of machine made sand particles is conducted to compare the differences between ordinary machine made sand and high-quality machine made sand.Experiments have shown that due to the anisotropy of particles,the three-dimensional morphology characterization of machine-made sand particles can accurately and intuitively characterize the particle shape and morphology.A high-quality morphology evaluation method for machine-made sand has been proposed.The comprehensive index of grain shape for river sand,granite mechanism sand,basalt mechanism sand,limestone A mechanism sand,and limestone B mechanism sand are0.75,0.73,0.71,0.72,and 0.67,respectively.River sand has the best particle shape,followed by granite,and ordinary limestone B has the worst mechanism sand.High quality limestone A mechanism sand has a better particle shape than ordinary limestone B mechanism sand.(2)By investigating the crushing conditions of limestone using conical vertical,counterattack,and vertical axis impact crushers,the impact on the particle size and morphology of machine made sand was studied,and relevant methylene blue titration tests were carried out.The results showed that the finished machine made sand of the vertical axis impact crusher had a "more than two ends,less in the middle" and good particle shape.The distribution of the finished machine made sand of the counterattack crusher was uniform,and the grading curve was smooth,but the particle shape was poor.The MB value(methylene blue value)of the mechanism sand significantly increases with the increase of the specific surface area and total pore volume of the stone powder.The change in the average pore size of the stone powder causes the MB value of the mechanism sand to fluctuate up and down,and there is no significant relationship between the average pore size and the change in MB value.The size of MB value is obviously related to the composition of clay minerals in stone powder,and is related to the cation exchange capacity of clay minerals.The stronger the exchange capacity is,the higher the MB value is.(3)Four types of machine-made sand with different lithology and particle shapes were selected as the research objects,and 15 grading distributions were designed.Rheological parameters and mechanical properties of machine-made sand mortar were tested,and concrete was subjected to viscosity reduction treatment.The results showed that the rheological properties of machine-made sand mortar were related to the stone powder content and total specific surface area in the grading design.Grades with large specific surface area had poorer rheological parameters,Its thixotropy decreases with the increase of average particle size.The rheological properties of high-quality limestone A-type sand with symmetrical particles such as square and spherical shape are better than that of ordinary limestone B-type sand with high content of needle and sheet shape.The addition of viscosity reducing materials helps to improve the working performance of machine made sand concrete.Micro beads can effectively reduce the plastic viscosity of cement concrete.Adding only 10% of micro beads can reduce the plastic viscosity by about 60%,with a significant effect.