A Study of Tricalcium Silicate Hydration From Very Early to Very Late Stages
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A STUDY OF TRICALCIUM SILICATE HYDRATION FROM VERY EARLY TO VERY LATE STAGES
S.A. RODGER*, G.W. GROVES*, N.J. CLAYDEN** AND C.M. DOBSON** *Dept. of Metallurgy and Science of Materials, Parks Road, Oxford University, OXl 3PH, England **Inorganic Chemistry Laboratory, South Parks Road, Oxford University, OXl 3QR, England
ABSTRACT The hydration of a tricalcium silicate paste has been examined from very early stages, i.e. during the induction period, up to two and half years using both scanning and transmission electron microscopy as well as This latter technique can be used solid state nuclear magnetic resonance. to reveal the degree of hydration of the sample and the nature of the siliSolid state NMR shows that during cate units which make up the C-S-H gel. the induction period a small amount of material containing hydrated monomeric silicate units is formed, although this is difficult to identify using SEM. However during the acceleratory period SEM shows the development of the typical fibrillar C-S-H material. Backscattered electron imaging shows the cores of anhydrous material surrounded by the denser inner product. Thermogravimetric analysis has been used to find the C/S ratio of this material, which is approximately 1.8, whilst solid state NMR shows that the hydrated silicate units are largely dimeric at this stage. As hydration proceeds, the fracture surfaces become increasingly dominated by large calcium hydroxide crystals, although some fibrillar material can be identified even after over two years. The C-S-H contains progressively more middle units in silicate chains at the expense of the end units. A sample of tricalcium silicate hydrated for 26 years has also been examined. INTRODUCTION In this paper we shall present the results obtained from a study of the hydration of tricalcium silicate using a number of complementary techniques. This has enabled us to build up a more accurate picture of the hydration process. In particular the use of a combination of electron microscopical techniques means that certain slightly misleading results can be corrected. It is clear from a recent comprehensive review by Taylor [1] that there is still no widely accepted explanation for some of the major features of the hydration process of C3 S. For example there remain many theories for the existence and termination of the induction period, each supported by various sets of researchers. However they can be broadly classified into two categories: the first considers the formation and destruction of a barrier layer to produce the induction period, whilst the second considers delayed nucleation and growth of either calcium hydroxide or C-S-H to be important. However there does seem to be a more general agreement that the later deceleration of the reaction is due to a buildup of C-S-H around the remaining anhydrous grains, impeding the access of water to the grains and diffusion of material away from the interface. In this study we have used a variety of electron microscopical techniques as well as solid state nuclear magnetic
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