Study of fractured surfaces of concrete caused by projectile impact

In recent years several studies presented different parameters and criteria to describe the damage of concrete specimens caused by projectile impact. The parameter used most to characterize damage is the volume of the craters on the front and rear side of the concrete specimen. In this study the damage of concrete specimens is described as a fractured area. In order to describe the whole fractured area it is necessary to consider the crater surfaces and the fractured surface area of the fragments generated by impact. The crater surfaces were analysed using a 3-dimensional laser-scanner system. The fragments were measured with a camera particle analyser. Their surfaces were determined taking into account the following parameters: Feret diameter, length, volume distribution and sphericity. A triaxial ellipsoid model was developed by means of these parameters. The whole fractured surface area is given by the sum of the specimen surface after perforating and the fragments surface minus the specimen surface before perforation. The fragment surface is decisive for the fractured surface and depends on the number of fragments of each size class. This study confirms previously gained results using new parameters: A larger maximum aggregate diameter enhances the impact resistance of concrete against projectiles.