Liesegang pattern development in carbonating traditional lime mortars

Liesegang patterns, generally rings, bands, spheres or spirals, form in far-from-equilibrium systems in nature and in the laboratory by self-organized periodic precipitation of sparingly soluble phases following a nonlinear reaction-diffusion process. Although Liesegang patterns have been known for...

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Published in:Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences Mathematical, physical, and engineering sciences, 2002-09, Vol.458 (2025), p.2261-2273
Main Authors: Rodriguez-Navarro, Carlos, Cazalla, Olga, Elert, Kerstin, Sebastian, Eduardo
Format: Article
Language:English
Subjects:
Architectural Conservation
Calcite
Calcium carbonates
Calcium Hydroxide
Carbonation
Crystals
Liesegang Patterns
Lime Mortars
Mineral precipitation
Mortars
Nucleation
Porosity
Supersaturation
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Summary:Liesegang patterns, generally rings, bands, spheres or spirals, form in far-from-equilibrium systems in nature and in the laboratory by self-organized periodic precipitation of sparingly soluble phases following a nonlinear reaction-diffusion process. Although Liesegang patterns have been known for more than hundred years, there is still disagreement as to the mechanisms underlying this phenomenon. Most studies have focused on Liesegang pattern formation in gels, quantitative studies of quasiperiodic patterns in non-conventional porous media (e.g. construction materials) being rare. Here, we report the development of 'revert' three-dimensional Liesegang patterns (i.e. concentric ellipsoids) in traditional lime mortars undergoing carbonation. Portlandite (Ca(OH)2) in a quartz (SiO2) sand aggregate, transforms into calcite (Ca(CO)3) in contact with atmospheric CO2, resulting in banded cementation of the lime mortar. Surprisingly, well-developed Liesegang patterns only occur in mortars prepared using 'aged' lime putty, kept under excess water for years, following an ancient Roman recipe to improve slaked lime quality; the carbonation of these mortars being faster than in pattern-less ones. The smaller Ca(OH)2 particle size in the long-term-aged putty enhances dissolution and increases the ion-concentration product, while creating a higher volume of pores with r < 0.1 m. These small pores can sustain very high supersaturation ratios with respect to CaCO3, resulting in higher nucleation rates, a crucial fact for pattern development previously neglected. These results may have strong implications for the understanding of Liesegang patterns, as well as for the conservation of architectural heritage.
ISSN:1364-5021
1471-2946
DOI:10.1098/rspa.2002.0975