Modeling rheological behavior of highly flowable mortar using concepts of particle and fluid mechanics

Abstract A particle–fluid model is developed for predicting the relationship between the shear stress and shear strain rate of highly flowable mortars. In this model, mortars are considered as a two-phase material, containing a fluid matrix (cement paste) and a group of well-graded, non-cohesive, and rigid particles (fine aggregate) that are uniformly distributed in the matrix. The mortar shear stress is assumed to be the sum of the shear stresses resulting from the paste flow, the aggregate particle movement, and the interaction between the cement paste and aggregate. The shear stress resulting from the paste flow is assessed using constitutive equations. The shear stress resulting from the aggregate particle movement is evaluated based on the probability and mechanical concepts of aggregate particle collision. The shear stress resulting from the interaction between the paste and aggregate is considered as the normal stress that the moving aggregate particles apply onto the cement paste. The shear rate of the mortar is obtained from the rheological definition of viscosity. Using this model, the effects of mortar mixture properties (such as aggregate size, volume, gradation, and friction as well as paste viscosity and yield stress) on mortar rheology are studied.

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