Structural Studies of Hydrated Tricalcium Silicate by Neutron Powder Diffraction K. MORI a, * , K. YATSUYANAGI b , K. OISHI b , T. FUKUNAGA a , T. KAMIYAMA c , T. ISHIGAKI d , A. HOSHIKAWA c , S. HARJO c , K. IWASE c , K. ITOH a and M. KAWAI c a Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan; b Institute of Technology, Shimizu Corporation, 3-4-17, Etchujima, Koto-ku, Tokyo 135-8530, Japan; c Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki 305-0801, Japan; d Department of Materials Science and Engineering, Muroran Institute for Technology, Muroran 050-8585, Japan Structure refinements have been carried out on the pure tricalcium silicate (C 3 S) and the hydrated C 3 S with the D 2 O–C 3 S mass ratio, which is 0.5, using neutron powder diffraction (NPD). The multi-phase Rietveld analysis of the hydrated C 3 S revealed the coexistence with the Ca(OD) 2 (trigonal phase) and the unhydrated C 3 S (triclinic one). The Ca(OD) 2 phase was hardly observed on the NPD patterns in the first ,6 h of hydration, while the several Bragg reflections of Ca(OD) 2 appeared drastically from ,6 to ,24 h, and then the hydration reaction rate was gradually suppressed. We could apply the Avrami-model to the initial hydration reaction process of C 3 S. Keywords: Tricalcium silicate; Neutron powder diffraction; Rietveld analysis; Hydration INTRODUCTION Tricalcium silicate (Ca 3 SiO 5 , so-called C 3 S or Alite) is the most principal component of Portland-cement clinkers (50 , 70 mass%). It is therefore expected that properties of the hardened cement paste are mostly characterized by the hydrated C 3 S. The hydration reaction formula of the C 3 S can be represented as follows [1]: Ca 3 SiO 5 þð3 þ y 2 xÞH 2 O! ðCaOÞ x ðSiO 2 ÞðH 2 OÞ y þð3 2 xÞCaðOHÞ 2 , where the first and second terms on the right side indicate a calcium silicate hydrate gel (C–S–H gel) and a calcium hydroxide, respectively. Actually, the hydration reaction rate of the cement is slow, so that it may be given by Ca 3 SiO 5 þð3 þ y 2 xÞH 2 O ! X{ðCaOÞ x ðSiO 2 ÞðH 2 OÞ y þð3 2 xÞCaðOHÞ 2 }þ ð1 2 XÞ{Ca 3 SiO 5 þð3 þ y 2 xÞH 2 O} (unhydrated), where X corresponds to the mass fraction of the hydrated C 3 S. Although the structural elucidation of the product during hydration is needed in order to clarify the hydration reaction process of the cement (or concrete), it seems that the detailed structure of the product is still in controversial, because the structural studies of C–S–H gel by the X-ray or the neutron powder diffraction (NPD) method are difficult extremely owing to the amorphous structure. On the other hand, the creation of the C–S–H gel are strongly associated with that of the Ca(OH) 2 and the unhydrated C 3 S, as can be seen from above hydration reaction formula. It implies that the quantifications of the crystalline Ca(OH) 2 and C 3 S within the product is very important ISSN 1023-8166 print/ISSN 1477-2655 online q 2005 Taylor & Francis Ltd DOI: 10.1080/10238160412331299519 *Corresponding author. E-mail: kmori@rri.kyoto-u.ac.jp Journal of Neutron Research, March–September 2005 Vol. 13 (1–3), pp. 163–167