Incorporation of Aluminum in the Calcium Silicate Hydrate (C−S−H) of Hydrated Portland Cements:  A High-Field ²⁷Al and ²⁹Si MAS NMR Investigation

Abstract

The calcium silicate hydrate (C-S-H) phase resulting from hydration of a white Portland cement (wPc) in water and in a 0.3 M NaAlO(2) solution has been investigated at 14 and 11 hydration times, respectively, ranging from 6 h to 1 year by (27)Al and (29)Si MAS NMR spectroscopy. (27)Al MAS NMR spectra recorded at 7.05, 9.39, 14.09, and 21.15 T have allowed a determination of the (27)Al isotropic chemical shift (delta(iso)) and quadrupolar product parameter (P(Q) = C(Q)) for tetrahedrally coordinated Al incorporated in the C-S-H phase and for a pentacoordinated Al site. The latter site may originate from Al(3+) substituting for Ca(2+) ions situated in the interlayers of the C-S-H structure. The spectral region for octahedrally coordinated Al displays resonances from ettringite, monosulfate, and a third aluminate hydrate phase (delta(iso) = 5.0 ppm and P(Q) = 1.20 MHz). The latter phase is tentatively ascribed to a less-crystalline aluminate gel or calcium aluminate hydrate. The tetrahedral Al incorporated in the C-S-H phase has been quantitatively determined from (27)Al MAS spectra at 14.09 T and indirectly observed quantitatively in (29)Si MAS NMR spectra by the Q(2)(1Al) resonance at -81.0 ppm. A linear correlation is observed between the (29)Si MAS NMR intensity for the Q(2)(1Al) resonance and the quantity of Al incorporated in the C-S-H phase from (27)Al MAS NMR for the different samples of hydrated wPc. This correlation supports the assignment of the resonance at delta(iso)((29)Si) = -81.0 ppm to a Q(2)(1Al) site in the C-S-H phase and the assignment of the (27)Al resonance at delta(iso)((27)Al) = 74.6 ppm, characterized by P(Q)((27)Al) = 4.5 MHz, to tetrahedrally coordinated Al in the C-S-H. Finally, it is shown that hydration of wPc in a NaAlO(2) solution results in a C-S-H phase with a longer mean chain length of SiO(4) tetrahedra and an increased quantity of Al incorporated in the chain structure as compared to the C-S-H phase resulting from hydration of wPc in water.

(Micro)-structural comparison between geopolymers, alkali-activated slag cement and Portland cement

“…The two other main resonances appear at approximately −80 and −86 ppm and originate from the SiQ 1 (disilicates or chain end groups) and SiQ 2 (middle groups in chains) units, respectively. 24 29 Si MAS-NMR spectrum of AAS sample (Fig. 4(C)) shows some non-negligible differences compared to that of PC sample.…”

“…The second one at 8 ppm could correspond to the isotropic chemical shift of the monosulfate phase, C 4 AŜH 12 (δ iso = 11.8 ppm), and of the tetracalcium aluminate hydrate phase, C 4 AH 13 (δ iso = 10.2 ppm) (the chemical shift difference can be due to a large amount of disorder as these two phases are unobserved by XRD). 24,25 27 Al MAS-NMR spectrum of AAS sample is very different (Fig. 3(C)); it shows a major content of tetrahedrally coordinated Al in connection with the large band centred at 59 ppm and a lower amount of octahedrally coordinated Al related to the band at 8 ppm.…”

Characterization and Preliminary Assessment of a Sorbent Produced by Accelerated Mineral Carbonation

“…The 1 H- 29 Si cross polarization spectrum of CASM showed a broad nondistinct peak similar to that of the 29 Si MAS spectrum. This indicates that the Si phase contains OH groups or water molecules in the immediate vicinity of the silicon atoms.…”

“…Replacement of one or more Si atoms by Al atoms in the outer coordination sphere ofaQ n unit results in lower field shifts (i.e., less negative δ values), arising from deshielding. A signal maximum at 103 ppm for the chemical shift distribution of the CASM 29 Si spectrum showed that the silicate groups are primarily organized in three-dimensional networks of Q 3 (-95 to -103 ppm), Q 4 (-103 to -120 ppm), and Q 4 (1 Al) (-97 to -108 ppm) silicate tetrahedra. Small fractions of silicon were present as Q 3 (1 Al) (-89 to -97 ppm) and Q 2 (-85 to -95 ppm) environments.…”

Gamma irradiation resistance of an early age slag-blended cement matrix for nuclear waste encapsulation

“…These bands remain in the hydrated samples, although with a reduced intensity, indicating that a significant fraction of unreacted material is still present in these cements, consistent with the early age of the cementitious grouts studied here. Upon hydration, new bands centered at -81 ppm and -85 ppm are observed, and these are assigned to the Q 2 (1Al) and Q 2 sites typically identified in C-A-S-H type products 23 . This confirms that even at early ages of curing, the main binding phase forming in the BFS-PC grout is an…”