Structural characterization of C–S–H and C–A–S–H samples—Part II: Local environment investigated by spectroscopic analyses

Incorporation of aluminium in calcium-silicate-hydrates

“…7) show the presence of IV-, V-and VI-fold coordinated aluminium, in agreement with literature [11,13,14,47]. The 27 29 Si NMR data is with 0.06 somewhat lower than the total Al/Si ratio from mass balance of 0.1, consistent with the presence of some [48]) but the amount is probably below the detection limit of TGA and XRD which is the raison why it was not observed previously.…”

“…Sun et al [11] suggested that Al(V) and Al(VI) could compensate the negative charge introduced by the replacement of Si(+ IV) by Al(+ III) in the silica chain. However, the amount of Al(V) and Al(VI) does not correlate with the amount of Al(IV) in the silica chains [10,13].…”

“…At higher Ca/Si ratios, the relative amount of Al(IV) in C-S-H decreases, instead more octahedrally coordinated Al(VI) is observed [10,11,13,14]. The octrahedrally coordinated Al(VI) has been suggested to represent either an amorphous aluminium hydroxide or a calcium aluminate hydrate at the C-S-H surface: third aluminium hydrate (TAH) [15] or in the interlayer within the C-S-H [13].…”

“…The octrahedrally coordinated Al(VI) has been suggested to represent either an amorphous aluminium hydroxide or a calcium aluminate hydrate at the C-S-H surface: third aluminium hydrate (TAH) [15] or in the interlayer within the C-S-H [13]. In addition to Al(IV) and Al(VI), approximately 10% of the aluminium associated with C-S-H is present as pentacoordinated Al(V) regardless the Ca/Si ratio of the C-S-H [10,13,14]. Sun et al [11] suggested that Al(V) and Al(VI) could compensate the negative charge introduced by the replacement of Si(+ IV) by Al(+ III) in the silica chain.…”

“…While there is a number of studies focused on the effects of aluminium uptake on the C-S-H structure [10,11,[13][14][15], very little data is available on the relations between the dissolved aluminium, calcium, silicon and hydroxide concentrations in the aqueous (pore) solution and the aluminium uptake in C-S-H, with the exception of a recent paper of Pardal et al [17], where relatively high aluminium concentrations (1 mmol/L) and short reaction times (1 day) have been used. The lack of systematic experimental data at equilibrium conditions hinders the development of adequate thermodynamic models which would allow prediction of the aluminium uptake in C-S-H.…”