skip to main content

SciTech ConnectSciTech Connect

Title: Carbonation of C–S–H and C–A–S–H samples studied by {sup 13}C, {sup 27}Al and {sup 29}Si MAS NMR spectroscopy

Synthesized calcium silicate hydrate (C–S–H) samples with Ca/Si ratios of 0.66, 1.0, and 1.5 have been exposed to atmospheric CO{sub 2} at room temperature and high relative humidity and studied after one to 12 weeks. {sup 29}Si NMR reveals that the decomposition of C–S–H caused by carbonation involves two steps and that the decomposition rate decreases with increasing Ca/Si ratio. The first step is a gradual decalcification of the C–S–H where calcium is removed from the interlayer and defect sites in the silicate chains until Ca/Si = 0.67 is reached, ideally corresponding to infinite silicate chains. In the seconds step, calcium from the principal layers is consumed, resulting in the final decomposition of the C–S–H and the formation of an amorphous silica phase composed of Q{sup 3} and Q{sup 4} silicate tetrahedra. The amount of solid carbonates and of carbonate ions in a hydrous environment increases with increasing Ca/Si ratio for the C–S–H, as shown by {sup 13}C NMR. For C–A–S–H samples with Ca/Si = 1.0 and 1.5, {sup 27}Al NMR demonstrates that all aluminium sites associated with the C–S–H are consumed during the carbonation reactions and incorporated mainly as tetrahedral Al(–OSi){sub 4} units in the amorphous silica phase. Amore » small amount of penta-coordinated Al sites has also been identified in the silica phase.« less
Authors:
;
Publication Date:
OSTI Identifier:
22475502
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 71; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; ALUMINIUM 27; CALCIUM; CALCIUM CARBONATES; CALCIUM SILICATES; CARBON 13; CARBON DIOXIDE; DECOMPOSITION; HUMIDITY; HYDRATES; LAYERS; MICROSTRUCTURE; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; SILICA; SILICON 29; TEMPERATURE RANGE 0273-0400 K