Griffith Fracture Criterion and Concrete

The original Griffith fracture criteria was developed to describe the rapid extension of a crack in a homogeneous elastic body. To check the applicability of the Griffith theory to portland cement systems which are neither elastic nor homogeneous, specimens of hardened cement paste, mortar and concrete made with normal and lightweight aggregates, and with notches of varying lengths were tested in flexure and in tension. While the paste specimens were notch-sensitive, mortar and concrete strengths were independent of notch length. The notch-insensitivity of mortar and concrete appears to be due to their composite nature. Similar behavior occurs in glass-Al²O³, fiberglass-reinforced epoxy and tungsten-reinforced copper composites. It appears that for mortar and concrete the direct application of Griffith criteria is not valid up to a certain length of cracks. This critical length depends on the size, volume, and type of aggregate.