Study On Basic Properties Of Typical Lithologic Machine-made Aggregate And Grading

Machine-made aggregate has become the main source of aggregate for construction projects.There are many kinds of parent rocks in our country with different characteristics.The quality of the machine-made aggregate produced by crushing,screening and shaping with different production processes is bound to be different.In order to make clear the basic properties of typical lithologic aggregate,the optimization and reasonable grading of machine-made sand,and the difference between machine-made sand stone powder and mud powder(montmorillonite),our research has carried out a systematic study on the scientific and technical system of machine-made aggregate in China.The main research contents and results are as follows:(1)The study of typical lithology shows that limestone is the most suitable rock for the preparation of aggregate.Limestone aggregate which is easy processing and crushing has good physical and chemical properties,good fragility,low abrasiveness,low adsorption and good water demand behavior.Siliceous rock is generally hard rock,and basalt and diabase have poor fragility,especially basalt aggregate has the largest abrasiveness,the lowest crushing index and the second is granite.In general,the energy consumption of processing and crushing of siliceous rock and the wear ratio of metal parts are high;Stone powder and machine-made sand of different lithology with a certain amount of admixture mainly affect the fluidity rather than the strength of cement-based materials.Siliceous aggregate has poor influence on the fluidity,while basalt aggregate has good properties except for high processing cost and slightly poor particle shape.(2)The results of SEM show that stone powder also has angularity;there are still grain shape problems in 1.18mm-0.6mm and 0.6mm-0.3mm grain size of machine-made sand;the grain size of 0.3mm-0.15 mm is better;the anti freezing and thawing performance of coarse aggregate of different lithology is good;the water saturation coefficient of coarse aggregate of different lithology is about 0.6-0.7.(3)It is reasonable to divide the grading area of machine-made sand in the T/CBMF38-2018,T/CAATB001-2018 aggregate for high performance concrete.The study on the grading of limestone machine-made sand with C30 concrete shows that on the premise that the other particle sizes meet the grading and grading requirements of this specification,the total amount of 0.15 mm,0.3mm and 0.6mm should be kept above 55%,and the range of0.15 mm can be widened to 0-30%.The 0.3mm particle size should not exceed the standardrange and have obvious effect on water retention of concrete;the 0.6mm particle size should not be lower than the lower limit of the standard,and the effect is not good when it is lower than 10%.If the 0.6mm particle size exceeds the standard by more than 40%,the ratio of the total particle size below 2.36 mm to the total particle size above 2.36 mm should be greater than 3 when the other particle size does not exceed the standard;the 1.18 mm particle size should be greater than 3 for concrete The cohesion of soil has a certain effect,but it is not significant and should not exceed the upper limit;for C50 concrete,the machine-made sand which is too coarse or too fine will lead to poor state of concrete mixture,so the scope of grade I of this specification is more appropriate.In general,the particle content of 0.3 and0.6mm should not be lower than the limit of the standard.(4)The montmorillonite is rather different from the high adsorptable manufactured sand powder,so the amount of mud powder must be strictly restricted during the production process of mechanism sand.The fine particle size high adsorption and large water demand ratio of the mud,which is extremely adverse to the durability of the concrete and seriously threatens the engineering quality and does not have the application conditions,will greatly reduce the fluidity and strength of the cement-based materials.However,the machine-made sand containing a large amount of limestone powder and a certain amount of high adsorption stone powder has certain application conditions.Although the amount of admixture has increased,the workability and strength can meet the requirements of low and medium strength concrete grade.