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A significant cause of building deterioration is the erosion of surfaces through rainwater runoff, a process which can be accelerated by attack by air pollution, including acid rain. In order to make an accurate diagnosis of the problem, it is necessary to identify which agents of deterioration are present and to estimate the rate at which the material is being lost. This can be done rapidly and directly by measuring the amount of dissolved and suspended material removed in the water runoff and then calculating mass balances.
This paper proposes procedures for performing this type of measurement, including the apparatus required, the major variables and ions to be analyzed, and the interpretation of results. The general approach is to isolate a test area of the building surface so that the water flowing over it can be collected. The water can be either rainfall or distilled water sprayed on the building. If rainfall is the source of the runoff, samples of the incident runoff also must be collected to complete the mass balance. The collected sample is analyzed for concentrations of ions characteristic of the building materials under examination, such as aluminum, calcium, iron, and silicon. In addition, ions related to air pollution—such as sulfates and nitrates—are measured.
erosion, stone deterioration, acid rain, runoff, carbonate dissolution, building diagnostics
Research associate, University of Maryland, College Park, MD