Abstract: The experimental study on mode-Ⅱ fracture of concrete is a difficult and hot issue among concrete fracture problems. Tests on 6 groups including 24 specimens about fracture propagation and mode Ⅱ fracture toughness were carried out. The parameters of failure load, concrete strain of crack tip, and crack tip sliding displacement(CTSD) were obtained through P-ε (load and strain) curve, P-t (load and time) curve and P-CTSD (load and crack tip sliding displacement) curve. The directions of crack extension was not parallel to shear force direction, but expanded from the tip of precrack to the vicinity of loading point and displayed as inclined crack. Results showed that mode Ⅱ fracture toughness varied from 0.5 MPa·m^0.5 to 1.1 MPa·m^0.5, and increased with the shortening of the distance from the vicinity of loading point to precrack and with the increase of initial seam height ratio. Shear fracture is prone to happen with a high and narrow shear zone.

Key words: concrete, 4-point loading, shear fracture, fracture toughness, influencing factor