Nuclear Spin Relaxation and Water Self-diffusion in Hardening Magnesium Oxychloride Cement Nikolaus Nestlea,c, Petrik Galvosas3, Christian Zimmermannb, Marwan Dakkourib, and Jörg Kärger3 a Universität Leipzig, Abteilung Grenzflächenphysik, Linnestraße 5, D-04103 Leipzig b Universität Ulm, Abteilung Elektrochemie, D-89069 Ulm c present adress: Technische Universität München, Institut für Wasserchemie, Marchioninistraße 17, D-81377 München Reprint requests to Dr. N. N.; Fax: 089 7095 7999, e-mail: nikolaus.nestle@physik.uni-leipzig.de Z. Naturforsch. 56 a, 561-564 (2001); received May 18, 2001 In this contribution, we report the results of NMR studies of the behaviour of water in a hydrating Sorel cement paste with a composition close to the stoichiometric optimum. Both the transverse spin-relaxation behaviour and water self-diffusion were studied in two separate experiments performed on samples on the basis of the same formulation. While there is a very strong initial decrease in the transverse relaxation time of the water in the paste, the diffusion coefficient is found to decrease mainly at later times of the hydration process where the decrease of the transverse relaxation time has already strongly slowed down. After about 6 h of the hardening process, the signal intensity available for a pulsed gradient diffusometry experiment is not sufficient any more for reliable measurements of the diffusion coefficients. Key words: Oxychloride Cement; Diffusion; Magnetic Resonance. Magnesium oxychloride cements (first described by Sorel [1]) are primarily used as a jointless floor ing material. They are also used in certain plaster and stucco applications and as binder for the produc tion of light-weight construction plates from coarse wood chips. Mg oxychloride cement is also discussed as a possible material for preventing mining dam ages from old salt mines and for sealing hazardous waste dumps in such old mines [2]. Compared to other binder systems, such as portland cement and gypsum, magnesium oxychloride cement provides a higher mechanical strength [3]. Oxychloride cements are typically prepared from MgO powder and a highly concentrated solution of MgCl2. In contrast to classical cement materials, the pH values for such pastes are typically in the acidic range. For practical application of oxychloride ce ments one is usually interested in a composition close to a molar ratio of (5:1:13) of (MgO : MgCl 2 : wa ter) [4]. Oxychloride hydrate phases of this compo sition are also important in the formation of early strength of the hardening mixtures. Water transport processes play a crucial role in the hardening of the oxychloride cements, and also in the later carbonatization and corrosion processes. NMR relaxometry and diffusometry offer a destruc tion-free approach for studying the dynamics of the fluid pore water in hydrating construction materials such as ordinary cements [5, 6], slag cements [7, 8] and gypsum [9]. Here, we report the application of these techniques to magnesium oxychloride cements. Materials and Methods Magnesium oxychloride cement samples were pre pared from food grade “heavy” magnesium oxide powder obtained from Merck, Darmstadt, and from a 5 M watery solution of magnesium chloride hexahy- drate (analytical grade, also from Merck, Darmstadt). Pastes were mixed from 5 g MgO and 5 ml of the MgCl 2 solution by means of mechanical stirring with a plastics (PVC) rod in small rectangular polypropy lene containers. For the experiments, the samples were filled either in plastics sample tubes produced from disposable 3 ml polypropylene syringes with a Luer-Lock connector (Becton-Dickinson, Meylan, France) for the relaxometry studies or in small seg ments of 5 mm diameter glass tubes of about 1.5 cm 0932-0784 / 01 / 0800-0561 $ 06.00 © Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com