Sensitive building materials such as calcareous stone are subject to accelerated deterioration by several agents. These may be physical processes such as freeze-thaw cycles, chemical processes such as reaction with sulfur dioxide gas, or biological processes such as attack by microorganisms. We are now beginning to understand some of these processes though our knowledge is very limited.
This project is oriented toward obtaining an improved understanding of pathways for air pollution damage to limestone buildings. In particular, we have been studying some of these pathways at the Cathedral of Learning, a 42- story limestone building on the University of Pittsburgh campus in Pittsburgh, Pennsylvania. Although the focus has been on this building, the larger goal of this project is to extend experimental and modeling results to other historical buildings in need of preservation. Such information can help conservators who are deciding on a best course of action for a deteriorating building. e.g. cleaning, consolidation, or treatment.
Continuing studies within the Cathedral of Learning project can be classified into three Phases. Phase I consists of on-site measurements of atmospheric pollutant concentrations and deposition. In Phase II. a computer program is used to model the airflow around the Cathedral. Model results can be used to study mixing in the vicinity of the Cathedral or as input parameters for later modeling efforts. Finally. Phase III includes development and testing of mathematical models that describe physical events such as surface rain washing and mass transfer of atmospheric pollutants to building surfaces. In addition to the three Phases, several long-term undergraduate projects are in progress. These include developing a computer database for storage of project data, photo-documenting current soiling patterns on the Cathedral. measuring vertical wind speeds near the walls of the Cathedral, and developing devices for measurement of rain flux to the building walls.
This report summarizes the work conducted on the Cathedral of Learning project during the period November 15, 1996 to November 15. 1997. Each of the three Phases described above is represented in the report. Chapter 2 contains experimental procedures and a very brief summary of results for two types of samples that were obtained at the Cathedral Airborne particles collected on polycarbonate filters and particles deposited on vertical surrogate surfaces Chapter 3 discusses modeling of airflow and trajectories of individual raindrops near the Cathedral. In this chapter we first summarize a portion of the relevant literature. Second, we give a preliminary outline of the steps we intend to take for modeling airflow around the Cathedral. Third, we present a simple model for the trajectory of an individual raindrop in the flow field of a building. A brief summary of the fill report is given in Chapter 4. Finally, Appendix A contains a revised manuscript summarizing results from measurements of vertical gradients of airborne pollutant concentrations and deposition fluxes. This manuscript has appeared in preliminary form in a previous report for this project (Elycmezian et al., 1996). The revised version was submitted for publication to the Journal of the American Institute for Conservation on November 11, 1997.