Synthetic calcium carbonate improves the effectiveness of treatments with nanolime to contrast decay in highly porous limestone

Radek Ševčík,Lucia Mancini,Alberto Viani,Dita Machová,Gabriele Lanzafame,Marie-Sousai Appavou

doi:10.1038/s41598-019-51836-z

Abstract

Three synthetized polymorphs of calcium carbonate have been tested in combination with the suspension of nanolime particles as potential consolidating agents for contrasting stone decay and overcome some of the limitations of nanolime agents when applied to substrates with large porosity. The modifications induced in the pore network of the Maastricht limestone were analyzed with microscopy and in a non-invasive fashion with small angle neutron scattering and synchrotron radiation micro-computed tomography. A reduction in porosity and pore accessibility at the micrometric scale was detected with the latter technique, and ascribed to the improved pore-filling capacity of the consolidation agent containing CaCO3 particles. These were found to be effectively bound to the carbonated nanolime, strengthening the pore-matrix microstructure. Penetration depth and positive effect on porosity were found to depend on the particle size and shape. Absence of significant changes in the fractal nature of the pore surface at the nanoscale, was interpreted as indication of the negligible contribution of nanolime-based materials in the consolidation of stones with large porosity. However, the results indicate that in such cases, their effectiveness may be enhanced when used in combination with CaCO3 particles, owing to the synergic effect of chemical/structural compatibility and particle size distribution.

Highlights

Three synthetized polymorphs of calcium carbonate have been tested in combination with the suspension of nanolime particles as potential consolidating agents for contrasting stone decay and overcome some of the limitations of nanolime agents when applied to substrates with large porosity
We report on the synergic effect of calcium carbonate polymorphs, synthesized in the laboratory, in combination with nanolime for the consolidation of a highly porous stone (>50%), the well-known Maastricht limestone (ML)[19,26]
scanning electron microscopy (SEM) observations revealed that the good chemical and structural compatibility of CaCO3 with nanolime and limestone, helped to effectively bound nanolime

Summary

Introduction

Three synthetized polymorphs of calcium carbonate have been tested in combination with the suspension of nanolime particles as potential consolidating agents for contrasting stone decay and overcome some of the limitations of nanolime agents when applied to substrates with large porosity. A reduction in porosity and pore accessibility at the micrometric scale was detected with the latter technique, and ascribed to the improved pore-filling capacity of the consolidation agent containing CaCO3 particles These were found to be effectively bound to the carbonated nanolime, strengthening the pore-matrix microstructure. Colloidal suspensions of nanolime were introduced as a suitable alternative to lime water[8,13] These nanosized Ca(OH)[2] particles suspended in alcoholic solvents have been proposed for the treatment of different cultural heritage objects[13,14] and considered promising as consolidation agents[10,15,16]. In order to overcome the limitations of the fluid inclusion techniques, not last the damage of sample microstructure due to the applied pressure, in the latter case, measurements have been conducted by combining two fully non-invasive techniques, namely, small angle neutron scattering (SANS) and synchrotron radiation micro-computed tomography (SR-μCT)

Methods

Results

Conclusion