Influence Of Mixing Time On Homogeneity Of Modern Concrete Mixture

Homogeneity is the most outstanding property of modern concrete.The homogeneity of concrete includes the homogeneity of the mixture and the homogeneity of the hardened concrete,but the homogeneity of concrete mixture is the prerequisite to ensure the homogeneity of hardened concrete.Therefore,homogeneity of concrete mixture is mainly studied in this paper,especially the influence of mixing time.Under laboratory conditions,design the low water ratio concrete mixture that included the reference concrete,fly ash replacement rate of 40% of concrete and fly ash and slag each replace 20% of concrete,used the deviation of volume density and strength variation coefficient as the index,the influence of various factors on the homogeneity of concrete is analyzed and the microscopic characteristics of chloride ion permeability coefficient,super depth micro measuring method are used to reveal the different uniformity of concrete.The experimental results show that the volume density deviation ratio of the mixture of reference concrete and fly ash concrete increases with the increase of mixing time from 45 s to 90 s,which indicates that the homogeneity becomes worse,at the same time,the compressive strength of different age showed a larger increase,and continue to extend the mixing time,the increase in compressive strength slowed down and gradually stabilized.The bulk density deviation of the compound concrete mixture is small,when the mixing time between 45 s and 75 s,show that the admixture of concrete mixture has good uniformity in a short period of time,while the mixing time increased from 45 s to 75 s,the strength coefficient of variation tends to decrease,when further increase of stirring time,there is no obvious change.Therefore,without changing the production process under the premise of the appropriate,extension of the mixing time can improve the strength of concrete,but the mixing time will also affect the homogeneity of concrete,when selecting the best mixing time,the influence of the mixing time on the homogeneity and strength uniformity of the mixture should be considered.When the mixing time is insufficient,the concrete surface and the inside will appear a large number of uncollected uniform cementing material and aggregate.When mixing time is extended appropriately,will making the concrete evenly distributed,making the internal structure compact;internal and surface of concrete will appear a lot of pores,when further extend the mixing time.The effect of mixing time on the chloride ion permeability of concrete is consistent with the strength,that is to say,the concrete with good homogeneity will have a good durability.