Research On Evaluation Method Of Aggregate Grading Based On Workability

With the development of China's economy and the increasing level of urbanization,the concrete industry has entered a stage where large-flow ready-mixed concrete is the mainstay,and the demand for concrete aggregates is also increasing.However,China's natural gravel resources are gradually depleting,and the quality of artificial aggregates is worrying,which cannot meet the requirements of high-performance large-flow concrete.Optimizing aggregate grading for large flow concrete has huge economic and social benefits.Existing research and practice have shown that aggregate in cement concrete mainly plays a role of skeleton,while slurry plays a role of filling and lubrication,and the two influence each other and work together.Considering that modern concrete pumping construction often requires concrete to have higher fluidity,which makes the mortar-to-bone ratio(volume ratio)have a greater change compared to plastic concrete,this paper divides the slurry into a filled slurry that fills the gap between the aggregates and To study the effects of aggregate grading,lithology,workability requirements,strength grade,etc.on the amount of filling and encapsulating slurry attached to the aggregate slurry attached to the surface of the aggregate,and to try to establish a model for grading evaluation and optimization.as follows:1.Propose an analysis model based on workability of filled and wrapped slurry.This model comprehensively considers the static accumulation of aggregate and the relative movement of aggregate in the slurry.The influence of factors such as material lithology,stacking performance,and concrete strength grade on the amount of slurry is used to guide the evaluation of aggregate gradation.2.The stacking performance of fine aggregate is the priority for gradation selection,and the amount of coarse aggregate wrapping slurry is the priority for gradation selection.This is because the difference between the maximum particle size and the minimum particle size of the fine aggregate is large,and the single-grain grade of fine aggregate is also more finely divided,resulting in a large difference in the accumulation void ratio of fine aggregates of different grades;and coarse aggregate The particle size change multiple is relatively small,and the coarse aggregate single-grain grade is relatively coarse,and the porosity of different grades is not much different.3.The most reasonable gradation of machine-made sand is related to the sandstone nature of machine-made sand.Under the conditions of this study,the grade of high-adsorption sand(such as granite,andesite)should be coarser than that of low-absorption sand(such as limestone).This is because the finer aggregate with stronger adsorption is appropriately thickened.The way to reduce the specific surface area balances its higher adsorption;the smaller the aggregate particle size,the more obvious the influence of lithology on the thickness of the coating layer.This is because the small particle size aggregate has a larger specific surface area and different lithological aggregates adsorb.The difference in sex is strengthened;when the natural sand is used,the gradation ratio mechanism sand should befine.This is because the natural sand stone powder content is small,the grain type is also good,the overall specific surface area is small,and the gradation is appropriately thinned to make the specific surface area in Under the premise of a reasonable range,the amount of slurry is reduced by reducing the particle size of the aggregate and the thickness of the coating layer.4.For slurry with high fluidity,the geometric average particle size of the aggregate should be fine.This is because with the increase of the particle size of the aggregate,the thickness of the coating layer increases rapidly and the specific surface area of the aggregate decreases.The result of the action;the sand rate of the slurry with better fluidity should be increased,because the large fluid slurry needs fine aggregate to maintain its workability.5.The strength of the slurry with larger strength should be finer.This is due to the low water-binder ratio of the high-strength slurry,the viscosity of the slurry,and the increase in the particle size of the aggregate.The thickness of the coating layer increases rapidly;high strength The sand rate of concrete is low.This is because high-strength concrete tends to have a lower water-to-binder ratio and less segregation and bleeding,and high sand rate will also reduce its fluidity.