Microstructure and Fracture At the Cement Paste-Aggregate Interface

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Abstract
The mechanical behavior of concrete is thought to be affected by the microstructure of the paste-aggregate interface, which differs in several respects from the microstructure of bulk paste. General aspects of interfacial microstructure, which appear to be fairly well understood, are reviewed. Recent microstructural studies using backscattered electron imaging show that there is a zone along the interface (approximately 50 μm wide) within which there are generally few large unhydrated clinker grains, many large voids (greater than 5 μm), a generally porous microstructure, many hollow-shell hydration grains, and in some cases little calcium hydroxide. The tendency for cracks to develop or grow along the paste-aggregate interface is discussed in relation to specific features of the interfacial microstructure.

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