Quantification of thaumasite in cementitious materials by ²⁹Si {₁H} cross-polarization magic-angle spinning NMR spectroscopy

Abstract

29Si {1H} cross-polarization (CP) magic-angle spinning (MAS) nuclear nagnetic resonance (NMR) is shown to be a valuable tool for detection and quantification of thaumasite in cementitious systems. A 29Si {1H} CPIMAS NMR method for quantitative analysis of thaumasite employing 1H and 29Si rotating-frame relaxation times TH1p and TSi1p and the 1H—29Si CP time TSiH is introduced. The method is illustrated by determination of the thaumasite content in five laboratory samples containing carbonates and sulphates from different sources. The use of 29Si{lH} CP/MAS rather than 29Si MAS NMR for the detection of thaumasite is shown to reduce the instrument time by up to a factor of IOOO because of the large difference in 1H and 29 spin-lattice relaxation times (TH1 and TSi1) and the 29Si intensity gain by CP for this mineral. The non-standard behaviour of the 1H and 29 spin-lattice relaxation processes observed for some samples is shown to follow a decay exponential in t with time t. 27Al MAS NMR is used to quantify ettringite for some of the samples. In contrast to previous proposals on the mechanism for the formation of thaumasite, it is demonstrated using 29Si{lH} CP/MAS and 27Al MAS NMR that considerable quantities of thaumasite can be produced in virtually aluminium-free materials. 13C {lH} CP/MAS NMR of pure thaumasite shows its potential in characterizing the carbonate anions in this mineral.

Thermal Activation of a Pure Montmorillonite Clay and Its Reactivity in Cementitious Systems

“…Inversion–recovery (IR) 29 Si MAS NMR has been previously used with success to distinguish silicon environments in mixed-layer 2:1 clays and in the alite and belite phases of anhydrous Portland cements. , These studies have utilized the fact that the 29 Si spin–lattice relaxation for these systems is governed by dipole–dipole couplings between the nuclear spins and the electron spins of the unpaired electron in paramagnetic centers (i.e., Fe 3+ ) present in the materials as impurities. For this case, and in the absence of spin diffusion, the spin–lattice relaxation behavior for 29 Si can be described by the stretched exponential relationship: − M z ( t ) = M 0 false[ 1 − ( 1 + α ) .25em exp ( − t / T 1 ′ ] where M 0 is the equilibrium longitudinal magnetization, α ≤ 1 is a constant accounting for pulse imperfections (i.e., α = 1 for an ideal pulse), and T 1 ′ is the stretched exponential spin–lattice relaxation time.…”

Sensitivity enhancement in natural-abundance solid-state 33S MAS NMR spectroscopy employing adiabatic inversion pulses to the satellite transitions

“…The sample of ettringite, [Ca 6 Al 2 (OH) 12 ](SO 4 ) 3 AE 26H 2 O, was synthesized using the same procedure as in an earlier 27 Al MAS NMR study of this phase [20]. The purity of the sample was confirmed by powder XRD and 27 [21] of the decomposed material shows that it contains 58 ± 5 w/w% thaumasite, the remaining being a C-S-H phase as judged from a 29 Si MAS NMR spectrum.…”

“…Ettringite and thaumasite are two sulfate-containing cementitious materials of unknown 33 S C Q , g Q parameters for the sulfate ions, but for both of which we earlier have performed extensive 27 Al MAS [20] and 29 Si{ 1 H} CP/ MAS [21,24] NMR studies. The early single-crystal X-ray diffraction study [25] and the recent powder X-ray refinement [26] of the hexagonal ettringite structure (space group P31c) show that this phase includes three crystallographically independent sulfate ions, while thaumasite exhibits only a single SO 4 2À crystallographic site according to single-crystal XRD [27].…”

Pozzolanic reactivity of a calcined interstratified illite/smectite (70/30) clay

“…29 Si SR NMR spectra, employing 15-20 different recovery times in the range 0.5 s-8000 s, have been acquired for some of the heat-treated samples. When the spin-lattice relaxation is governed by dipole-dipole interactions with paramagnetic centers and spin-diffusion is absent, the spin-lattice relaxation behavior for the 29 Si nuclei can be described by a stretched exponential relationship [45][46][47]. The quartz peak overlaps with the resonances from the clay calcined at high temperatures and thus, two components have been assumed in the analysis of the quartz-peak intensities from the 29 Si SR NMR experiments, corresponding to the expression…”