Resumo

PUY-ALQUIZA, María Jesús et al. Characterization Petrophysical of the Losero Formation in the Historical Architecture of the Guanajuato city, Mexico. Ing. invest. y tecnol. [online]. 2013, vol.14, n.2, pp.191-205. ISSN 2594-0732.

The Losero Formation has made an important contribution to the cultural and architectural heritage of Guanajuato city. The green color attractive appearance of this stone and its ease to be worked adds a number of significant landmarks of Guanajuato city. It was the most important natural building stone in the Guanajuato in the XVIII and XIX centuries. The Losero Formation is generally used as load-bearing material and, due to its lower porosity, as basal facings of the examined buildings. It also represents the main architectural elements in Guanajuato city, which is considered a world heritage site. After almost a century of exposure, the Losero Formation presents a progressive decay in many buildings (corrosion, scaling, spalling lichens, and crack formation). In some cases partial and total replacements have been successful in the restoration work, a proper understanding of the cause of decay is necessary for conservation purposes and restoration methodologies. This paper reports the findings of a petrophysical study of the eight lithofacies most used of the Losero Formation in the restoration and construction of monuments in the city of Guanajuato (Los Morados, La Veta, Coleto, El Blanquito, El Moyejon, El Verde, La Perla, and La Cema), the names assigned to the lithofacies are informal and were called so by local stonemasons. This lithofacies were investigated by the techniques of optical microscopy; X-ray diffraction and Scanning Electron Microscopy (SEM) and physical properties (uniaxial compressive strength, capillarity water absorption, apparent and real density, total porosity) and durability using the salt crystallization test. The analytical results support that La Veta is the best lithofacie of Losero Formation which made it an ideal material for columns, pedestals, staircases, flooring, while that of La Cema cannot be used as pillars, balconies, and floors. The presence of calcite and kaolinite in La Veta and La Cema was not favorable for outdoor use. La Perla, El Moyejon and Coleto, were found to be an ideal material for columns, pedestals, staircases, flooring. Los Morados, El Blan-quito, and El Verde exhibited low strength and durability values so cannot be used as pillars, balconies, and floors. These materials, notwithstanding their different behavior towards decay agents, are all affected by similar weathering typologies that, in order of importance and extension are: back weathering, break out, discoloration, soiling, lichen and fissures. The rate of decay depends on the textural fabric properties of the lithofacies, on the pollution fluxes and on the environmental setting (air pollution, meteorological and micro-climatic conditions). The results obtained make it possible to choose suitable lithofacies for the replacement and substitution in the restoration processes in monument of the Guanajuato city.

Palavras-chave : Losero Formation; Guanajuato city; petrography; petrophysic; construction and restoration.

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