Application of thermal analysis in preservation and restoration of historic masonry materials: Part B. Degradation of materials (Conference Paper)

摘要

In part A, thermal analysis techniques were discussed to characterize masonry building materials from significant historic properties in the Charleston, South Carolina, area. In part B, thermal analysis confirms various modes of long-term degradation of the materials through environmental exposure. This research provides evidence of diagenesis within materials usually considered as chemically inert. Masonry mortars used in the nineteenth century include those composed of lime and sand in the early part of the period, with the use of natural (manufactured) cement in conjunction with the mid-century fortification of the harbor. Mortars with both types of binders have been found subject to chemical alteration by long-term reactions with intruding soluble salts to form phases rich in sulfur (primarily from ground salt intrusion) or rich in chloride (primarily from sea water intrusion). The general direction of reactions may be toward formation of smectite minerals found in salt water estuaries. Further, evidence of alkali-silica reaction was found in a mortar exposed to sea water. Differences were found in reactions between lime mortars and those containing natural cements in regard to reaction phenomena. Mineral phases as a result of chemical alteration were also found in "underfired" clay bricks. Thermal analysis techniques confirm the identities of new phases within the historic masonry materials. The results suggest new phases formed within the masonry elements have the potential to cause deterioration through salt crystallization phenomena.