Morphology and size distributions of secondary fragments formed during compressive fracture of cement‐based composites

ABSTRACT Eight cement‐based composite materials (concrete, mortar, lightweight concrete, cement paste) were tested in a force‐controlled compression testing machine in order to discuss their physical crushing behaviour. Secondary fragments formed during the fragmentation were collected and analysed. The analyses included size distribution parameters, density distribution parameters, fracture plane assessment and SEM imaging. Energy dissipative fracture phenomena were noted and described in detail. These phenomena were linked to the size distribution parameters of the fragments, which could be characterized through RRSB size distributions. The modular shapes of density distribution functions and their local ascents were also estimated and discussed. It was found that the analysis of size distribution and morphology of secondary fragments, formed during the crushing of cylinders in a force‐controlled testing machine, can deliver additional information about the fracture mechanisms involved in physical crushing processes. According to their fragment size distribution characteristics, the materials could be subdivided into two major groups: compact materials (concrete with homogeneous aggregate distribution, cement matrix) and compact–disperse materials (cement mortar; concrete with inhomogeneous aggregate distribution). A relative brittleness index (RBI) was derived. Composites with low RBI values behaved like compact materials, and it can be expected that their performance in technical crushing machines can be described with Kick's comminution hypothesis.