Calcite crystallization in the cement system: morphological diversity, growth mechanism and shape evolution

Abstract

Carbonation plays an indispensable role in engineering construction, embracing mineralization, CO2 sequestration and low pH induced corrosion, but the essential mechanism of carbonation occurring in calcium silicate hydrate or portlandite can hardly be interpreted. Observation on how carbonation proceeds at the nano scale is thus critical for a better understanding of its dynamics. Here, using electron microscopy combined with first-principles calculation, a new view on carbonation in the cement system is revealed, considering morphological diversity, growth mechanism and shape evolution. Two types of crystalline forms of calcium carbonate (i.e. cubic and spindle) under room conditions were observed and determined to be calcite, both experimentally and theoretically. The mechanism of morphological evolution of calcite in a cement system was demonstrated based on the theory of aqueous chemistry. The [Ca2+] to [CO3] ratio was the principle cause for the diversity in crystal morphology instead of the types of reactants (i.e. portlandite or calcium silicate hydrates). Excess calcium species in the solution could selectively adsorb on surfaces, resulting in an inhibitive effect on the growth of specific crystal faces, (1 0 4)calcite and (2 1 1[combining macron])calcite in this case. Furthermore, a relationship between relative ionic concentration and the length to diameter ratio was established to predict the shape transformation. This work makes it possible to explore the chemical nature of carbonation from a nano scope rather than being confined to the macroscopic carbonation of concrete.

The Effect of Hydrothermal Holding Time on The Characterization of Hydroxyapatite Synthesized from Green Mussel Shells

“…The crystalline phase on green mussel shells powder after calcination is non-uniform hexagonal (Figure 4(b)), which is typical of the portlandite or Ca(OH)2 phase. The morphology is in accordance with the research conducted by Jiang et al, [20]. Precipitated calcium carbonate (PCC) product has a uniform shape, in which there are spherical crystals that indicate the vaterite phase (Figure 4(c)).…”

“…In addition, at a low CO2 gas flow rate it will reduce the supersaturation of the solution due to the lack of availability of CO2 gas so that the supersaturation of the solution is low. At low supersaturation that causes aragonite particles to form [18][19][20][21][22][23][24][25].…”

(Hydroxy)apatite on cement: insights into a new surface treatment

“…Additionally, the SAED pattern of this near single crystal region (Fig. 6f1) shows several Bragg spots which match the position for calcite, 56,57 suggesting a relatively large calcite crystal. The TEM image of the biogenic treated cement sample (Fig.…”

Amorphous Polyphosphate and Ca‐Carbonate Nanoparticles Improve the Self‐Healing Properties of both Technical and Medical Cements

“…[ 13 ] This role of polyP is abolished after enzymatic hydrolysis of polyP via the ALP, an enzyme that is present on the surface of bacteria. [ 47,48 ] In the absence of polyP, ACC is readily transformed along the thermodynamic route to calcite, the final stabilizing crystals in the cement: [ 49 ] “direct carbonation.” As outlined in Figure 12, the process of ACC‐NP‐driven calcite formation/carbonation is termed “delayed carbonation. In addition, the introduction of ACC to the cement system allows a substitution of the Ca‐carbonate which is fabricated by the bacterial carbonic anhydrase.…”