| Manufactured sand is different from natural sand in particle gradation and particle morphology,and contains a large amount of fine,which has a significant impact on the workability of cement-based materials.The existing standards and studies are not enough to accurately characterize the properties of manufactured sand,even more difficult to reveal the quantitative influence of manufactured sand on cement-based materials.Therefore,based on the standard sand,the properties of manufactured sand and its influence on the properties of cement-based materials were studied experimentally.A comprehensive analysis of the manufactured sand produced by 12 different manufacturers shows that the aspect ratio,roundness,angularity and roughness are closely related to the particle diameter.The difference of aspect ratio,roundness and roughness between different manufactured sand is the smallest when the particle diameter is in the range of 0.30 mm～0.60 mm,while the difference of angularity is the smallest when the particle diameter is in the range of 0.60 mm～1.18 mm.The aspect ratio of manufactured sand is about 1.470～1.590,which is larger than that of river sand and standard sand;Roundness is about 0.737～0.793,which is less than that of standard sand and river sand;And there was a negative linear correlation between aspect ratio and roundness.In addition,the aspect ratio of manufactured sand is positively correlated with the bulk void fraction,and the roundness is negatively correlated with the bulk void fraction.Fine particles play a decisive role in the specific surface area of fine aggregate.The specific surface area of different manufactured sand varies greatly,fluctuating between 11.03 m~2/kg and 36.44 m~2/kg,which is significantly larger than that of standard sand(5.89 m~2/kg)and river sand(7.86 m~2/kg).There is an inverse relationship between the surface-dry water absorption and the specific surface area of the specific surface area and the fluidity ratio of the mortar.Compared with standard sand motor,under the same proportion of mixture,the fluidity of mortar decreases by 32%～46%,the setting time is shortened,and the flexural and compressive strength of tuff manufactured sand mortar increases by around 20%,but the influence of granite manufactured sand is small.Under the same fluidity,the water demand of manufactured sand increases by 18%～24%,the setting time is hardlyt affected,and the early-age compressive strength and flexural strength decrease by16%～36%and 5%～19%respectively,but manufactured sand has little effect on the strength later.Compared with standard sand motor,under the same proportion of mixture,the large surface-dry water absorption rate of manufactured sand,the fluidity decrease of mortar,the decrease of most probable aperture,the shift of pore size distribution to small pore size,and the increase of mesopore content,lead to the increase of the early-age shrinkage by 38.5%～107.4%.Under the same fluidity,only the manufactured sand with a particularly high surface-dry water absorption rate(2.4%)had an increased early-age shrinkage of mortar,while the other two groups had little effect on early-age shrinkage of mortar.This is due to the increase of water-cement ratio,which leads to the corresponding increase of the most probable aperture of mortar prepared by manufactured sand,and the decrease of the mesopore content.In order to make the manufactured sand concrete has the same workability as the natural sand concrete,it is necessary to increase the sand rate(2%～4%)and the slurry-bone ratio(0.037～0.080),when the slump is 40 mm～200 mm and the strength grade is C20～C45.When the water-cement ratio is the same,the adjustment of sand ratio and slurry-bone ratio does not affect the 28 d compressive strength,and the water binder ratio rule is still applicable to manufactured sand concrete.Under the same slump,the increment of the slurry-bone ratio of manufactured sand concrete compared with natural sand concrete increases with the increase of the strength grade. |
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