NaCl interaction during hydration as studied by NMR

NaCl interaction during hydration as studied by NMR

Pel, L. (Eindhoven University of Technology, the Netherlands)
Ji, Yanliang (Tongji University, China)
Sun, Zhenping (Tongji University, China)

2021-04-29

With freshwater getting scares seawater, i.e., water containing NaCl, can become the only viable option for making concrete. Although a lot of research had been directed to understanding the role of water in cement hydration, not much is known about the interaction of the Na+ and Cl- with cement paste during drying. A problem is that available techniques like, i.e., XRD, SEM, and EDX, for measuring the microstructure and the methods for determining the concentration of Na+, Cl- ions in pore solutions are either indirect or invasive and moreover often destructive, which consequently may lead to inadequate interpretations. Using a specially designed Nuclear Magnetic Resonance (NMR) setup, the 1H, 23Na and 35Cl content in cementitious materials can be measured quasi-simultaneously and hence give us direct information on the interaction of the ions and the microstructure development. We have studied the influence factor, i.e., the water-cement ratio, on the microstructure development and the binding of Cl- and Na+. It was found that during the initial hydration stage more Cl- is bound in comparison to Na+ . This is reversed during the acceleration period after which there is a preference for binding of Na+ in comparison to Cl-. Increase of W/C ratio results in less binding capability of Na+ and Cl-.

Sodium chloride
Cement-based materials
NMR
Hydration process

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