Experimental Investigation on the Mechanical Properties of Mortar-aggregate Interface and Its Use in Meso-scale Numerical Simulation of Concrete

Mortar-aggregate interface is the weakest region in concrete in terms of the mechanical properties due to its relatively higher porosity compared with the surrounding bulk cement paste, which has a significant effect on the behavior of concrete when subjected to loading. As a result, the mechanical properties of the interface have been recognized as the principal condition for the meso-scale numerical modeling of the fracture process of concrete and concrete structures. In this study, the composite mortar-aggregate specimens with different surface roughness of aggregate and mortar strength were prepared to quantitatively investigate the mechanical properties of interface by means of a series of tests, including the splitting tensile test, the direct shear test and the three-point bending test. The test results indicated that the mechanical properties of interface to some extent depend on the strength grade of mortar and the roughness of aggregate surface. The failure mode largely depends on the fracture energy of mortar cohesion layer and the joint adhesion layer. It is also found that the fracture energy of interface increases with the increase of mortar strength and the roughness of aggregate surface. With purpose of providing basic constitutive model for meso-scale numerical simulation of concrete behavior, the tension softening curves of mortar-aggregate interface for different mortar strength grade were developed based on the test results. Finally, with the proposed constitutive model of interface on meso-scale, the response of plain concrete under loading were conducted using the Rigid Body Spring Model (RBSM). The numerical simulation results indicated that the expressions of tension softening curves were valid and can be successfully applied to the numerical analysis of concrete structures.