Research On The Influence Of Dolomite Powder On The Performance Of Machine-made Sand Concret

With the rapid development of highway construction in Guizhou,natural sand resources are seriously scarce,and machine-made sand has become the main construction sand in Guizhou.A large amount of waste stone powder will be produced in the production process of machine-made sand,and the content of stone powder in machine-made sand is generally greater than the current standard limit,which will adversely affect the performance of high pier structures of bridges in mountainous areas.The powder removal process can reduce the content of stone powder in the machine-made sand,but it will cause waste of stone powder resources and is not conducive to controlling production costs.Therefore,this paper uses this part of stone powder resources to study the influence of stone powder content on the performance of machine-made sand concrete,determine the maximum limit of stone powder content,and recycle waste stone powder,which is in line with the concept of green development.In this paper,the manufactured sand concrete（D-I,D-II）with 5%,10%,15%,20%,25%and 30%dolomite powder（0-80μm,0-150μm）was taken as the research object（Note:Dolomite powder was directly added as admixture）.The influence of fineness and content of dolomite powder on the performance of manufactured sand concrete was studied through the tests of working performance,mechanical properties and chloride ion penetration resistance.The appropriate fineness and content of dolomite powder to effectively improve the performance of concrete were proposed.The influence of dolomite powder on the micro structure of manufactured sand concrete was analyzed by SEM scanning electron microscopy.Finally,the relationship between the strength of each mechanical property and the relationship between strength and content were established by fitting according to the experimental data.The conclusions are as follows:（1）When dolomite stone powder is added,the slump of machine-made sand concrete decreases with the increase of dosage.Under the same dosage,the slump of concrete in group D-II is larger,and D_IIstone powder is better than D_I.（2）When dolomite powder is added,the mechanical properties（cube compressive strength,flexural strength,splitting tensile strength,axial compressive strength and static compressive elastic modulus）of manufactured sand concrete increase first and then decrease with the increase of stone powder content.The mechanical properties of concrete with 15%content of D_Istone powder and 20%content of D_IIstone powder are good,and the mechanical properties of concrete with D_II-20(D_IIcontent is 20%)are the best.Its 28d cube compressive strength,flexural strength,splitting tensile strength,axial compressive strength and elastic modulus are increased by 25%,25.8%,32.1%,31.2%and 11.4%respectively compared with the reference group JZ.（3）The resistance to chloride ion permeability of manufactured sand concrete increases first and then decreases with the increase of dolomite powder content.The resistance to chloride ion permeability is the best when 15%D_IIis added,and the electric flux is reduced by 23.7%compared with JZ.D_Iis better than D_IIwhen the dosage is lower than 10%,and D_IIis better than D_Iwhen the dosage is higher than 15%.（4）The interface characteristics were analyzed by scanning electron microscopy.The addition of appropriate amount of dolomite powder can improve the compactness of the micro structure of manufactured sand concrete,which plays a good micro-aggregate filling effect and micro-crystal nucleus effect.（5）According to the test data,the strength correlation is fitted and analyzed,and the fitting curves and formulas of flexural strength,splitting tensile strength,axial compressive strength and cubic compressive strength are obtained.The relationship between the mechanical properties and the content of stone powder is obtained.