Abstract
La Cruz dam is a hydraulic concrete structure placed in a hilly rural area near to the city of Azul (Buenos Aires Province, Argentina). Lichen colonization was detected in the dam so the aim of this paper is to study the characteristics of the cementitious substrate, to identify the lichen species and to assess their potential negative action. Cementitious mortar samples were brought to the laboratory in order to study their water absorption rate, density, pH and alkali concentration. Lichens have been sampled by scraping them out of the substrate. The dam wall is colonized mainly byCaloplaca citrina, which is different from the situation observed in nearby rocks and the Tandil dam, where other species were also found. The lichen and the superficial layer were analyzed with infrared spectrometry and oxalic acid was detected indicating a chemical degradation of the surface. Except for this negative action due to the lichen, the cementitious mortar samples have good pH, density and porosity characteristics, and no external evidence of sulphation or alkalisilica reaction were observed. In conclusion, the lichen acts superficially and causes only an aesthetical problem with no structural risk to the dam, but only an aesthetical problem, therefore no actions are recommended.
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