Weathering effects of an historic building in San Francisco de Campeche, Mexico

Abstract

This research presents a qualitative description of the degradation phenomena that occurred in external walls of the San Carlos Bastion, San Francisco de Campeche, Campeche City, (Mexico), a military structure built with calcareous materials between 16th and 17th centuries. Several weathering structures were identified in mortars and limestone. Scanning Electron Microscopy coupled to Energy Dispersive (sem/eds), X-Ray Diffraction (XRD) and Optical Microscopy (OM) analysis were carried out in order to identify the nature of the weathering compounds. These include: carbonate crusts (CaCO₃), as well as neomineral phases (e.g. whewellite [CaC₂O₄.H₂O] and weddellite [CaC₂O₄2H₂O]) related to microbial activity. Results indicate that the tropical climate induces physical, chemical and biological effects in the building materials, due mainly to high relative humidity. The influence of relative humidity appears to be the cause that damage the building, more than the action of sea salts and atmospheric pollutants. Furthermore, the presence of elements, such as chlorine, sodium and sulfur indicate that weathering occurred through synergistic processes during long-time exposure to the tropical environment of San Francisco de Campeche.