A size effect is a fundamental phenomenon in concrete materials. It denotes that both the nominal structural strength and material brittleness always decrease with increasing element size under tension. The objective of the paper is to investigate a mechanical size…
A size effect is a fundamental phenomenon in concrete materials. It denotes that both the nominal structural strength and material brittleness always decrease with increasing element size under tension. The objective of the paper is to investigate a mechanical size effect in plain concrete. The focus was on meso-structural phenomena contributing to different failure modes in the post- peak region. The experimental programme was carried out on concrete specimens of the diameter D=74, 100, 150, 200 and 250 mm during tensile splitting. The strength and ductility of specimens decreased with increasing specimen diameter. The concrete meso-structure was determined with the very advanced x-ray micro-tomography system and was next implemented into numerical calculations. The size effect calculations were performed for all experimental concrete specimens with the three-dimensional spherical discrete element model YADE. Concrete was depicted as a four-phase composite material including aggregate, cement matrix, interfacial transition zones (ITZs) and macro-voids. 2D and 3D calculations were performed. The process of micro- and macro- cracking was studied in detail for three various failure modes, including the quasi-brittle, brittle and snap-back behaviour. The macroscopic stress-CMOD curves and shapes of cracks were directly compared with the laboratory test outcomes. The evolutions of broken contacts, normal and tangential displacements were elaborated at the aggregate level.