CHARACTERIZATION OF THE PASTE-AGGREGATE INTERFACIAL TRANSITION ZONE SURFACE-ROUGHNESS AND ITS RELATIONSHIP TO THE FRACTURE-TOUGHNESS OF CONCRETE

Notched concrete beams containing varying amounts of pea gravel aggreg ate were tested under three-point bend, and their fracture toughness d etermined. The roughness of the region near the interface between the cement paste and the aggregate was evaluated by digitizing images from a confocal tandem scanning microscope. The average roughness of the p aste was found to be related to the fracture parameters K-IC (critical stress intensity factor) and Delta a(c) (critical crack extension), a s determined by the two-parameter fracture model. The roughness in the proximity of the paste-aggregate interface was generally higher than that of the paste far from the aggregate, and it decreased with the di stance from the aggregate. This study indicates that aggregate particl es increase the toughness of the cement paste portion of concrete, and that this is an important mechanism for toughening concrete.