Service life prediction of exposed natural stone used as construction material in historic buildings

The conservation and reuse of architectural heritage and existing buildings represent a critical and challenging task in preserving the identity of our cities, with a wide range of disciplines and expertise finding application within its practise. Especially in urban settings, they have to confront the threats posed by external agents, where phenomena as acid rain have been proven to account for a significant acceleration factor in the process of building stone decay, with long-term effects over both the aesthetic and mechanical properties of the component. Furthermore, recent concerns are raised in relation to the climate emergency, with a projected severe increase in the process of decay in high rainfall areas as Scotland.

Within the conservation process, maintenance represents a major aspect, referring to either a planned/preventive maintenance or corrective/unplanned maintenance. If the first is defined by a scheduled action based on prevention, this last refers to an unforeseen action often involving replacements, at the expenses of the integrity and authenticity of the asset. In this context, it was shown that the possibility of anticipating the type and amount of preventive maintenance needed, helps to considerably reduce the costs over time, beside significantly prolonging the service life of the building.

Based on these premises, the question is whether a threshold for preventive maintenance of natural building stone can be predicted with sufficient accuracy before replacement becomes inevitable. Weathering is a time-related cumulative mechanism resulting from incremental processes controlled by a combination of exogenous parameters and intrinsic factors to the building component. This cause-effect relationship can potentially support the establishment of a performance profile for the construction material within its service environment, allowing projections to be carried over the combined effect of specific setting parameters and the properties of the building component.