Scaling of fracture and Acoustic Emission in the compression of concrete-like materials

A combined compression and AE test is proposed, in order to study the scaling of fracture and Acoustic Emission in concrete-like specimens with different size and slenderness. The cylindrical concrete specimens were drilled from two pilasters sustaining a viaduct along an Italian highway built in the 1950s. A two-dimensional FEM numerical model of the pure compression tests is also presented, which is able to describe both the discrete cracking at the matrix-aggregate interface and the smeared cracking of the matrix. The adopted mesoscale modeling directly accounts for the aggregate dimensional distribution, being each aggregate explicitly represented. The distribution of aggregate size and position was generated according to the Füller distribution. In this way, the crack patterns can be simulated correctly, as well as the load displacement curve. During microcrack propagation, acoustic emission events can be clearly detected experimentally. Therefore, the number of acoustic emissions can be put into relation with the number of Gauss points in the finite element model where cracking takes place. A good correlation is found between the amount of cracking simulated numerically and the experimental acoustic emission counting for different specimen sizes, and the two quantities show the same exponent with respect to the considered volume. This evidence reconfirms the assumption, provided by fragmentation theories, that the energy dissipation during microcrack propagation occurs in a fractal domain comprised between a surface and the specimen volume.