title: Consolidation of archaeological gypsum plaster by bacterial biomineralization of calcium carbonate.
abstract: Gypsum plasterworks and decorative surfaces are easily degraded, especially when exposed to humidity, and thus they require protection and/or consolidation. However, the conservation of historical gypsum-based structural and decorative materials by conventional organic and inorganic consolidants shows limited efficacy. Here, a new method based on the bioconsolidation capacity of carbonatogenic bacteria inhabiting the material was assayed on historical gypsum plasters and compared with conventional consolidation treatments (ethyl silicate; methylacrylate-ethylmethacrylate copolymer and polyvinyl butyral). Conventional products do not reach in-depth consolidation, typically forming a thin impervious surface layer which blocks pores. In contrast, the bacterial treatment produces vaterite (CaCO3) biocement, which does not block pores and produces a good level of consolidation, both at the surface and in-depth, as shown by drilling resistance measurement system analyses. Transmission electron microscopy analyses show that bacterial vaterite cement formed via oriented aggregation of CaCO3 nanoparticles (∼20nm in size), resulting in mesocrystals which incorporate bacterial biopolymers. Such a biocomposite has superior mechanical properties, thus explaining the fact that drilling resistance of bioconsolidated gypsum plasters is within the range of inorganic calcite materials of equivalent porosity, despite the fact that the bacterial vaterite cement accounts for only a 0.02 solid volume fraction. Bacterial bioconsolidation is proposed for the effective consolidation of this type of material. The potential applications of bacterial calcium carbonate consolidation of gypsum biomaterials used as bone graft substitutes are discussed.
authors.affiliation: Department of Microbiology, Faculty of Sciences, University of Granada, Avda Fuentenueva s/n, 18002 Granada, Spain.
authors.forename: Fadwa
authors.initials: F
authors.lastname: Jroundi
authors.affiliation: Department of Microbiology, Faculty of Sciences, University of Granada, Avda Fuentenueva s/n, 18002 Granada, Spain.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Gonzalez-Muñoz
authors.affiliation: Department of Painting, Faculty of Fine Arts, University of Granada, Avda Andalucía s/n, 18071 Granada, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Garcia-Bueno
authors.affiliation: Department of Mineralogy and Petrology, Faculty of Sciences, University of Granada, Avda Fuentenueva s/n, 18071 Granada, Spain. Electronic address: carlosrn@ugr.es.
authors.forename: Carlos
authors.initials: C
authors.lastname: Rodriguez-Navarro
mesh_terms: D001106:Archaeology; D001672:Biocompatible Materials / Q000737:chemistry*; D002119:Calcium Carbonate / Q000737:chemistry*; D002133:Calcium Sulfate / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008903:Minerals / Q000737:chemistry*; D016062:Porosity; D013030:Spain; D013818:Thermogravimetry; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D008903:Minerals; D002119:Calcium Carbonate; D002133:Calcium Sulfate
keywords: Biomineralization; Calcium carbonate; Conservation; Gypsum plaster; Vaterite