Nonlinear Rheological Modeling Of Fresh Cementitious Materials

Fresh cementitious materials often display shear thickening or shear thinning.Therefore,the nonlinear rheological models should be used to describe the rheological behavior of fresh cementitious materials.To date,the modified Bingham and Herschel-Bulkley models are commonly utilized nonlinear rheological models of fresh cementitious materials.However,the solution of Couette inverse problem based on these two rheological models has serious theoretical errors,so that the rheological parameters of these two rheological models can not be correctly measured with rheometer.For the purpose that the nonlinear rheological models can be perfectly applied to research on the properties of fresh cementitious materials,this dissertation studied the Couette inverse problem,the physical significance of parameters in the nonlinear rheological models,the method for handling rheological test data measured in the presence of plug flow,the influence degree of rheological measurement process on the heterogeneity of fresh cementitious materials and the application of nonlinear rheological models in the study of fresh cementitious materials.The main research contents and conclusions are listed as follows:(1)Through the derivation of the integral expressions to solve the Couette inverse problem under the coaxial cylinders rheometer,the errors of the Couette inverse problem based on the modified Bingham and Herschel-Bulkley models have been corrected.The correct solution of the Couette inverse problem based on these two models was given.(2)Through comparison and analysis,the modified Bingham model was replaced with the Parabolic model,and the Herschel-Bulkley model was replaced with the newly established Exponential model.Compared with the modified Bingham model and the Herschel-Bulkley model,the Parabolic model and the Exponential model are more suitable for the study of rheological properties of fresh cementitious materials because the parameters in the Parabolic model and the Exponential model can be measured with rheometer.(3)By establishing the relationship between the Couette inverse problem under the coaxial non-cylinders rheometer and the Couette inverse problem under the coaxial cylinders rheometer,the solution and the corresponding equations of the Couette inverse problem under the coaxial non-cylinders rheometer based on the Bingham model,the Parabolic model and the Exponential model were given.The analytical solution of the Couette inverse problem under the coaxial non-cylinders rheometer can be obtained by measuring the proportionality coefficient in the sets of equations.(4)In the process of dealing with rheological test data,it is necessary to judge whether the data are measured in the presence of plug flow.When calculating rheological parameters,the measured rheological data pairs of rotation speed and torque should be eliminated from small to large point by point,and the rheological parameters should be calculated repeatedly until that the calculated minimum shear stress is not less than the yield stress.(5)A rheological scheme is designed,which consists of the ascending stage in which the rotational speed stepwise increases with time and the descending stage in which the rotational speed stepwise decreases with time.The “rotation speed--torque” diagram is drawn by utilized the average values of stabilized rotational speed and torque on these steps.The absolute value of the influence degree of rheological measurement process on the heterogeneity of fluid can be characterized by the area of ring surrounded by the ascending stage and the descending stage.The relative value of the influence degree of rheological measurement process on the heterogeneity of fluid can be characterized by the ratio between the area of ring surrounded by the ascending stage and the descending stage and the area of ring surrounded by the ascending stage and its projection on the rotation speed axis.The reliability of the rheological parameters measured and calculated by the corresponding rheological scheme can be characterized by the percentage of the difference between one and the ratio of the ring areas.The experimental results show that the reliability can be used to effectively evaluate the influence of rheological measurement process on the heterogeneity of fresh cementitious materials.