Double cross-polarization MAS NMR in the assignment of abundant-spin resonances: 19F-{29Si}-19F FBCP/MAS NMR of fluoride ions incorporated in calcium silicate hydrate (C-S-H) phases

► A new version of the double-cross polarization NMR experiment: Forth and Back CP. ► Detection of the high-γ spins for assignment of resonances for these abundant spins. ► Experimental demonstration by 19F-{29Si}-19F and 19F-{13C}-19F FBCP/MAS NMR spectra. ► Assignment of 19F resonances for fluoride in calcium silicate hydrate (C-S-H) phases.