Theoretical and experimental study on shear behavior of fresh mortar

The shear behavior of fresh mortar is investigated using a force balance approach. In this approach, fresh mortar is considered as a two-phase material containing a matrix of cement paste and a group of rigid, spherical, non-cohesive aggregate particles. The shear resistance of a micro unit mortar is first assessed based on the friction between two contacted particles and the shear force carried by the cement paste of the micro unit mortar. The shear force of a macro-unit mortar is then calculated based on the number of the contacted aggregate particles in the mortar and the shear force carried by the rest of the cement paste. Forty-seven fresh mortar mixtures made with aggregate and paste having different characteristics and mix proportions are tested using a direct shear apparatus. The study indicates that the shear behavior of mortar follows the Mohr-Coulomb equation. The newly developed model can well predict the shear behavior of mortar materials and explain the direct shear test results.