The hydrogen network in kaolinite and tetracalcium monocarboaluminate hydrate from 1H MAS NMR at very high magnetic field and spinning frequencies

Hydroxyl groups or water molecules are crucial in the stabilization of hydrated materials with lamellar structures such as clays and AFm phases due to their strong hydrogen bondings. The hydrogen networks in kaolinite and monocarbonate have been analyzed using 1 H MAS NMR at very high magnetic field (22.3 T) and very high spinning frequencies (40–100 kHz). The four hydrogen sites in kaolinite (Al 2 Si 2 O 5 (OH) 4 ) have been resolved by 1 H MAS NMR and assigned to the crystal structure using the relationship between 1 H chemical shift and hydrogen bonding strength. Monocarbonate ([Ca 4 Al 2 (OH) 12 ]·CO 3 ·5H 2 O) includes 5 interlayer water molecules and 12 framework hydroxyl groups. Resonances from the five water molecules and 11 out of 12 hydroxyls have been resolved by single-pulse 1 H MAS NMR and a 1 H – 1 H double-quantum – single-quantum correlation NMR experiment, utilizing very high-speed spinning (100 kHz) and partial deuteration to reduce strong 1 H – 1 H dipolar interactions. A full assignment of all resonances to the distinct hydrogen sites in monocarbonate has been achieved based on the two-dimensional correlation experiment and calculations of relative dipolar coupling strengths for possible 1 H – 1 H spin pairs. The present study demonstrates a significant advancement in the degree of resolution that can be achieved by high-resolution 1 H NMR for cement minerals, which may be utilized to explore hydrogen networks in more complex cementitious systems.