Modeling of phase interfaces during pre-critical crack growth in concrete

Recent developments in the Rigid-Body-Spring Network (RBSN) modeling of concrete are presented, with candid assessments of research needs for the modeling of pre-critical crack growth under multi-axial stress conditions. Fracture of micro-concrete specimens is investigated through the combined use of such discrete (lattice) models, X-ray tomography, and imaging techniques. The specimens contain small amounts (10–50 wt.% fraction) of spherical glass aggregates. Acid-etching of the glass aggregate surfaces is done to vary the bond properties of the matrix–aggregate interface. Tomographic images of the unloaded specimens provide the initial configurations of the three-dimensional lattice models, which are based on a three-phase representation of the material meso-structure: fine-grained mortar matrix, glass aggregate inclusions, and matrix–aggregate interfaces. The numerical and physical test results agree well with respect to peak loads and the associated crack patterns. Material structure and interface properties affect pre-critical cracking, in accordance with expectations. Dependence of composite strength on aggregate content and arrangement is studied through simulations of large sets of nominally identical models, which differ only in random positioning of the aggregates.