Study On Rheological Properties Of Manufactured Sand Mortar Based On Compact Packing

With the acceleration of infrastructure construction,natural sand resources are increasingly scarce.Considering the protection of natural sand and environmental protection,manufactured sand,as a new type of green and sustainable fine aggregate,has been widely used.However,the poor grain shape,packing density,grading composition and stone powder content of manufactured sand are the main factors affecting its practical application,among which the packing density and working performance are the most prominent.The compressible packing model(CPM model)can improve the packing density of manufactured sand,but the traditional CPM model does not consider the effect of grain shape on the packing density.In this paper,a particle action effect coefficient considering the effect of grain shape is proposed to modify the CPM model.At the same time,based on the modified CPM model,the influence of grain shape,gradation composition,compactness of manufactured sand and stone powder,surplus coefficient of slurry on the rheological properties of mortar are studied.The main research work and results are as follows:(1)Digital Image Processing technology was used to obtain five grain shape parameters of manufactured sand,including aspect ratio,roundness,inner diameter ratio,flattening ratio and sphericity,to reflect the morphological characteristics of manufactured sand particles.The grain shape composite index(P)is obtained by adding up the five parameters according to different weights.The grain shape composite index(P)of sandstone manufactured sand,granite manufactured sand,sandstone(Pebble)manufactured sand and limestone manufactured sand used in this paper are 0.657,0.669,0.683 and 0.695 respectively.The higher the comprehensive index of grain shape(P)of manufactured sand is,the closer the particles are to spherical shape,the better the grain shape is,and the higher the packing density is under the same gradation.(2)Based on the obtained grain shape composite index(P),a particle effect coefficient "L" is introduced to modify the virtual packing density in the traditional CPM model,and the function expression of the particle effect coefficient "L" is obtained by numerical analysis.The modified CPM model can accurately predict the actual packing density of four grain graded manufactured sand,and obtain the grading composition of manufactured sand in the most compact packing state.(3)With the decrease of packing density and the number of coarse particles,the yield stress of manufactured sand mortar first decreases and then increases.When the yield stress decreases,the lower grain shape composite index(P)of manufactured sand is,the greater the decline of yield stress is.With the decrease of the compactness of the manufactured sand,the plastic viscosity of the mortar gradually increases and the fluidity gradually decreases,and the working performance is the best when the manufactured sand is most closely packed.The hysteresis loop area of mortar increases with the increase of accumulated porosity,but the increase decreases when the accumulated porosity exceeds 47% ～ 48%.(4)With the increase of the amount of stone powder,the yield stress of mortar increases gradually.The yield stress of mortar is affected by the particle size and shape of the stone powder.Under the same amount of stone powder,if the diameter of stone powder is small and the particle shape is poor,the yield stress of mortar is large.When the content of stone powder is lower than 12.5%,due to the effect of filling,the plastic viscosity of mortar decreases and the fluidity increases with the increase of stone powder content.When the dosage is 12.5% ～30%,due to the large specific surface area of stone powder,the plastic viscosity of mortar increases and the fluidity decreases.(5)When the water cement ratio is 0.5,under the premise of ensuring the closest accumulation of manufactured sand and keeping the content of stone powder unchanged,the yield stress and plastic viscosity of manufactured sand mortar decrease and the fluidity increases with the increase of slurry surplus coefficient from 1.05 to 1.65.The decline rate of plastic viscosity can be roughly divided into three stages: fast,slow and fast again,corresponding to three states of slurry shortage,sufficiency and surplus.The mortar performance is the best when the mortar is in sufficient volume.After considering the economic and practical aspects,the optimal slurry surplus coefficient of sandstone manufactured sand mortar,granite manufactured sand mortar and limestone manufactured sand mortar is 1.35,while the optimal slurry surplus coefficient of sandstone(Pebble)manufactured sand mortar is 1.45.At the same time,the 28-day compressive strength of mortar is the highest under the optimal slurry surplus coefficient.