Fracture parametric study on cement-based materials from three-point bending test

For two most basal cement-based materials, cement paste and mortar, their fracture parameters were studied by 84 geometrically similar three-point bending beams of which strength and size were varied. Complete load versus crack mouth opening displacement (PCMOD) curves were directly obtained, and their fracture toughness were determined. In the test, a sudden brittle fracture was not found in cement paste and an apparent stable crack propagation before unstable failure was observed both in cement paste and mortar. The process of crack initiation, stable extension and unstable failure were investigated using resistant strain gauges. There exist obvious size effects both in the critical crack mouth opening displacement and critical crack tip opening displacement of cement paste and mortar. Due to the influence of shrinkage crack and the precritical crack propagation length, the initial fracture toughness K-Ic(ini) and unstable fracture toughness K-Ic(un) are not size-independent.