Natural abundance high field 43Casolid state NMR in cement science

Abstract

This work is a systematic attempt to determine the possibilities and the limitations of the ⁴³Ca high field solid state NMR in the study of cement-based materials. The low natural abundance (0.135%) and small gyromagnetic ratio of ⁴³Ca present a serious challenge even in a high magnetic field. The NMR spectra of a number of cement compounds of known structure and composition are examined. The spectra of several phases important in cement science, e.g., anhydrous beta di-calcium silicate (β-C₂S) and tri-calcium (C₃S) silicate were obtained for the first time and the relation of spectroscopic and structural parameters is discussed. The method was also applied to the hydrated C₃S and synthetic calcium silicate hydrates (C–S–H) of different composition in order to understand the state of calcium and transformations in the structure during hydrolysis. The spectra of hydrated C₃S reveals a calcium environment similar to that of the C–S–H samples and 11 Å Tobermorite. These observations support the validity of using layered crystalline C–S–H systems as structural models for the C–S–H that forms in the hydration of Portland cement.