Progressive Changes in the Structure of Hardened C₃S Cement Pastes due to Carbonation

Abstract

The structures of partially carbonated hardened C3S cement pastes have been investigated by a combination of 29Si magic angle spinning nuclear magnetic resonance spectroscopy and analytical transmission electron microscopy, supported by X-ray diffraction and thermogravimetric analysis. Progressive changes in structure are reported for thin slices for a paste carbonated in pure COz for times from 1 to 16 h, and the results are compared with those for a paste carbonated for 2 months in air. C-S-H gel of reduced Ca:Si ratio and increased silicate polymerization was formed during the early stages of carbonation. The morphology of the original C-S-H was, in the main, retained. A cross-linked silica-rich gel formed at later times in paste carbonated in C 0 2 but not up to the time of 2 months in air. Calcium carbonate took the form of microcrystals of vaterite and calcite which formed dense masses between gel fibrils and around partially reacted CH crystals, possibly accounting for the observed slowing in the rate of reaction of CH with time.[

Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties

“…• C is consistent with data from the literature in the case of accelerated conditions of carbonation [12,8,5,68,46,69,4,47]. Sauman [13] attributes the first peak (750…”

“…This phenomenon has already been highlighted in the literature [45,5,68]. It would be related to a reduction of accessibility of CH cristals due to the formation of a coating of CC which would hinder CH dissolution.…”

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

“…In the literature, it has been widely reported that carbonation products of hydrated cementitious minerals are calcium carbonate, modified silica gel, and alumina gel (10,42,43). This allows us to suggest that both anhydrous and hydrated calcium silicate/aluminate minerals found naturally or as constituents of wastes (i.e., ash, slag, and construction waste) represent suitable raw materials for sorbent production by accelerated carbonation.…”

Effect of CO<SUB>2</SUB> Carbonation on the Chemical Properties of Waste Cement: CEC and the Heavy Metal Adsorption Ability

“…The carbonation of C-S-H gel forms acid-stable silica gel (Q 3 and Q 4 ). According to recent studies, 14,15) a higher degree of carbonation of the hardened OPC leads to produce a higher crystallinity of the calcite and greater polymerization of the silica gel. Figure 5 presents X-ray diffraction patterns of the waste cements carbonated at various carbonation times.…”