Development of technique for observing pores in hardened cement paste.pdf

Development of technique for observing pores in hardened cement paste Kyoji Tanakaa,*, Kiyofumi Kurumisawab aStructural Engineering Research Center, Tokyo Institute of Technology, 4259 Nagatuta, Midori-ku, Yokohama 226-8503, Japan bDepartment of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatuta, Midori-ku, Yokohama 226-8503, Japan Received 17 December 2001; accepted 15 March 2002 Abstract Mercury intrusion porosimetry is a widely used technique to determine the pore size distribution in porous materials. However, this technique does not provide information about the shapes and locations of pores. A new technique is developed, in which gallium (Ga) is used as an alternative intrusion liquid because of its property of being solid at normal room temperature (melting point: 29.8
C). This permits the examination of pores using image analysis. The technique is applied to hardened cement paste. The distribution of solid Ga is observed through an electron probe microanalyzer (EPMA), and the shapes and locations of pores in cement paste are discussed. D 2002 Elsevier Science Ltd. All rights reserved. Keywords: Microstructure; Image analysis; Cement paste; Gallium; Electron probe microanalyzer (EPMA) 1. Introduction Physical properties of concrete, particularly strength and permeability, significantly depend on its pore structure. Information about pore structure is, therefore, essential for understanding such physical properties. Examination of pore structure of concrete includes elucidation of the shapes, volumes, locations, and distribution of pores resulting from cement hydration. The significant dependence of the physical properties of concrete and mortar on their pore structures has attracted the attention of many researchers since early times, accumulat- ing a vast body of studies including those by Powers [1]. Understanding of pores was substantially enhanced by the development of the mercury intrusion porosimetry method, which provid