Raman study of the ageing test of natural hydraulic lime under the influence of industrial port activities

Abstract

AbstractRaman spectroscopy was applied for the diagnostic study of some commercial mortars applied to the outside of Punta Begoña Galleries, a historical building located in a coastal environment (Basque Country, Northern Spain) with industrial activities. Molecular analyses were carried out to study the conservation state of commercial materials exposed to the environmental stressors with the aim of being used for future restoration works of the Galleries and to assess in this way their stability when exposed to aggressive agents. The presence of the degradation compounds was studied considering the orientation of the walls where the commercial mortars were placed. Among the decay products, gypsum (CaSO4·2H2O) was identified in a higher number of samples together with sodium nitrate (nitratine, NaNO3) in a minor amount. The presence of magnesium‐based secondary products, nitromagnesite (Mg(NO3)2) and dypingite [Mg5(CO3)4(OH)2·5(H2O)], was also found formed by the degradation of original magnesium compounds of the mortars. Raman analyses showed in almost all the samples the presence of the xanthophyll carotenoid astaxanthin, which is considered as a bioindicator of pollution level because it appears as the first xanthophyll in highly contaminated areas. The presence of calcium oxalates whewellite (СаС2О4·Н2О) and wedellite (СаС2О4·2Н2О), formed probably as a result of secretion of microorganisms, was detected. However, these compounds were only identified in samples from the south‐west orientation, which is most affected by the influence of the harbour activity, indicating a higher anthropic impact in the materials in that area. Therefore, the choice of materials for restoration will have to be made considering the different environmental impacts. The obtained results were very useful to understand the deterioration processes on commercial mortars in order to study the atmospheric impact that these aggressive environments have on modern material in a relatively short period after their application.