Hybrid nano-composites for the consolidation of earthen masonry

Rachel Camerini; David Chelazzi; Rodorico Giorgi; Piero Baglioni

doi:10.1016/j.jcis.2018.12.082

Hybrid nano-composites for the consolidation of earthen masonry

J Colloid Interface Sci. 2019 Mar 15:539:504-515. doi: 10.1016/j.jcis.2018.12.082. Epub 2018 Dec 22.

Authors

Rachel Camerini¹, David Chelazzi², Rodorico Giorgi³, Piero Baglioni⁴

Affiliations

¹ CSGI and Department of Chemistry, University of Florence, via della Lastruccia 3-50019, Sesto Fiorentino, Italy. Electronic address: camerini@csgi.unifi.it.
² CSGI and Department of Chemistry, University of Florence, via della Lastruccia 3-50019, Sesto Fiorentino, Italy. Electronic address: chelazzi@csgi.unifi.it.
³ CSGI and Department of Chemistry, University of Florence, via della Lastruccia 3-50019, Sesto Fiorentino, Italy. Electronic address: giorgi@csgi.unifi.it.
⁴ CSGI and Department of Chemistry, University of Florence, via della Lastruccia 3-50019, Sesto Fiorentino, Italy. Electronic address: baglioni@csgi.unifi.it.

PMID: 30611046
DOI: 10.1016/j.jcis.2018.12.082

Abstract

Hypothesis: Earth is one of the oldest silicate-based materials in stone heritage, still largely used in architecture worldwide. Earthen materials are highly susceptible to wind and water erosion, leading to loss of cohesion and crumbling. Conventional consolidants (alkoxysilanes, synthetic or natural polymers) lack physico-chemical compatibility or effectiveness, and can promote degradation. We propose for the first time nano-composites for the surface consolidation of adobe, i.e. unbaked earth bricks often containing organic fibers and lime.

Experiments: We investigated, mimicking the setting of portland cement, the formation of calcium silicate hydrate (CSH) within adobe porosities, owing to the pozzolanic reaction between nanoparticles of silica and calcium hydroxide, to consolidate a powdery substrate. Different formulations were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), dynamic light scattering (DLS), and turbidimetry (UV-Vis spectroscopy).

Findings: A ternary composite made of SiO₂ nanoparticles, Ca(OH)₂ nanoparticles, and hydroxypropyl cellulose, dispersed in a (4:1) ethanol:water blend, was formulated. Each component is compatible with adobe, and plays a role in its consolidation. The treatment of adobe samples with the composite leads to the in situ formation of CSH, providing resistance to peeling, abrasion, and wet-dry cycles, with no aesthetic alteration. This opens new perpectives in the preservation of one of the most widely used construction materials.

Keywords: Adobe; Calcium hydroxide; Calcium silicate hydrate; Consolidation; Earthen masonry; Heritage preservation; Hydroxypropyl cellulose; Nano-composites; Silica.