Development And Application Of Rheological Model Analyzer Based On Thin Slice Shear Principle

The rheological properties of material play an important role in guiding the development,processing and application of material.Rheometer has been developed rapidly as an important tool for studying the rheological properties of material.The existing rheometers include capillary rheometer,rotational rheometer and dynamic shear rheometer,etc.,but they can only be used for the determination of some specific rheological parameters,that cannot fully reflect the rheological properties of materials.The rheological model can reflect the constitutive relationship of material.It is the most effective and feasible analytical method to accurately and comprehensively know the rheological properties of materials.In this way,the rheological properties of material can be obtained quickly and intuitively,the rheological model can also use for the analysis of viscoelasticity,plasticity of material in quantitative,and predict the rheological behavior of materials under different conditions.However,the existing rheometer is difficult for rheological modeling,so the development of a rheometer that can quickly and accurately establish a rheological models is of great significance.A rheometer used for the test of rheological properties and the establishment of rheological model was developed in this study,which based on the principle of thin slice shear.This rheometer can obtain the strain-time curve of the material under constant shear force,and establish the rheological model of the material by fitting and analyzing the curve.The rheological model of fresh cement-based material was established by using the new rheometer.The influence of water to cement ratio(w/c),sand to cement ratio(s/c),hydration time,water reducing agent and aggregate on the rheological properties of fresh cement-based material was analyzed.Some main conclusions can be draw as follow:(1)The structure and hardware of the new rheometer was designed in modularization based on the principle of thin slice shear,which use automatic loading or unloading device for imposing or unloading shear force on the sheet.The problem of instantaneous shock overload at the moment of application or unloading is solved.An intelligent measuring device was designed,which realizes the accurate measurement of material strain by monitoring the displacement of thin slices,and obtains the rheological curve of material under strain stress with time.(2)The material rheology modeling system is designed and developed,the obtained material rheology curve can be fitted and analyzed by this system.A material rheological model library was established to meet the difference requirement of different material rheological modeling.Different fitting algorithms were designed for different rheological models,and the optimal model screening algorithm was established to ensure the reliability of rheological modeling of each kind of material,and the rheological models and parameters of the materials can be obtained quickly and accurately.(3)The rheological modeling of fresh cement paste was analyzed by the new rheometer,the results show that the rheological model of fresh cement paste was transformed from the pot model(N)to Maxwell model(H-N)with the extension of hydration time,then transformed to Burgers model(N-H-N/H),and the model parameter value increased gradually.When the water to cement ratio is greater than 0.35,the growth rate of the initial model parameters of the fresh cement paste is significantly lower than that of the cement paste with water to cement ratio less than 0.35,which indicating the formation rate of the flocculation network structure is slowed down when the water to cement ratio is more than 0.35.(4)The rheological modeling of fresh mortar was analyzed by the new rheometer,the results show that the rheological model of fresh mortar evolved from Burgers model(N-H-N/H)to five element model(H-S/(N-S/H))with the decrease of water to cement ratio,the parameters of the model and the plastic yield value of fresh mortar increase with the increase of sand to cement ratio.The addition of water reducing agent has no significant effect on the rheological model of fresh cement mortar,but the hydration rate becomes slower with the increase of the amount of water reducing agent.(5)The rheological modeling of fresh concrete was analyzed by the new rheometer,the results indicate that the rheological model of fresh concrete is five element model(H-S/(N-S/H)).The parameter value of the rheological model increases gradually with the prolongation of hydration time,and the growth rate of the rheological model parameter gradually decreases when the aggregate content increases.The rheological model parameters of fresh concrete increase gradually with the increase of aggregate content,and when the ratio of aggregate to cement is greater than 3,the plastic parameter value of fresh concrete decreases,which indicate that the stability of fresh concrete would decrease as the content of the aggregate exceeds the threshold level.