Fracture testing of concrete

Fracture behaviour of plain and reinforced concrete beams was investigated both experimentally and analytically using fracture mechanics concepts. It was found that plainconcrete fractures occur when the applied stress intensity factor at the crack tip reaches a critical value. Steel reinforcement was found to reduce the effective stress intensity at thetip of propagating cracks due to their closing effect. It was found that reinforced beam fails when such effective stress intensity factor reaches the plain strain fracture toughness value for plain concrete. The closing stress intensity due to steel reinforcement was calculated and was found to be dependent on both the area of steel reinforcement in thesection and also the initial crack size. A modified closing stress intensity parameter independent of crack size was defined and used to quantitatively predict crack initiationresistance of reinforced concrete beams.Good agreement between fracture mechanics model prediction and theexperimental results indicates the suitability of fracture mechanics solution for crackinitiation in reinforced concrete sections.