An Enhanced Mix Design Method Of Self-compacting Concrete With Fly Ash Content Based On Paste Rheological Threshold Theory And Material Packing Characteristics

Self-compacting concrete is widely used in engineering for its good working performance and the excellent properties of optimizing the construction environment and improving the construction efficiency.The addition of fly ash has improved the hydration heat,cracking of the early concrete,and the mechanical properties and durability of the late concrete,which participates in the design of the self-compacting concrete mix ratio.The addition of fly ash replaced part of the cement,achieving economical and sustainable performance,and at the same time,improving the workability and mechanical properties of self-compacting concrete.The purpose of the research is to propose a mixing design method of self-compacting concrete with fly ash based on rheological threshold theory and realize the prediction of the working performance of self-compacting concrete from rheological parameters of paste,achieve simplifying the process of mix design of self-compacting concrete with fly ash,saving configuration self-compacting concrete materials,time and manpower,improving the design efficiency as well as.Firstly,the paper carried out an experimental verification of the existing rheological threshold theory,and found that when the fine aggregate gradation changes or fly ash is mixed,the calculation result of the original rheological threshold is no longer applicable,resulting in a mismatch between the self-compacting paste zone with the self-compacting concrete zone.Furthermore,the paper revises the original threshold calculation method from two aspects.On the one hand,the paper conducted a study on the reduction coefficient of fly ash in the mix design of the self-compacting concrete based on the physical and mechanical model of the influence of the yield strength and viscosity on the fluidity of the self-compacting concrete.A method of multiplying a fixed coefficient on the basis of the original threshold to characterize the effect of the particle size distribution of the fine aggregate is proposed,and the correction coefficient of the pure cement threshold is obtained when the sand rate is fixed.Then,an algorithm to obtain the fly ash reduction coefficient by moving the pulp area is proposed,and the reduction coefficient is obtained when the fly ash content is 20%,and a mixing ratio design method of self-compacting concrete is obtained based on the reduction coefficient of fly ash.On the other hand,based on the effect mechanism of fly ash on the rheology of the pulp,a basic water demand test of mortar was designed to obtain the bulk density of the mortar,and an equivalent bulk density was proposed to characterize fly ash and fine aggregate on the effect of particle size distribution on rheology of the past.Therefore,the calculation formulas of the original yield strength threshold and the viscosity threshold were revised,and the mix design method of self-compacting concrete with fly ash based on the paste rheological threshold theory and material packing characteristics was proposed.At the same time,in the process of drawing the self-compacting paste zone and the self-compacting concrete zone,and the bilinear interpolation method was used to analyze the results.Finally,a method based on the graphic area is proposed to quantitatively evaluate the prediction accuracy of the rheological parameters of paste for the self-compacting concrete performance.The average relative accuracy of the mix design method of the self-compacting concrete with fly ash based on the modified paste rheological threshold theory and material packing characteristics is 90%,which increase33% in accuracy.Finally,based on an engineering project,a qualified C50self-compacting concrete was successfully formulated through an enhanced mix design method of self-compacting concrete with fly ash content based on paste rheological threshold theory and material packing characteristics.