Impact of Mineralogy, Texture and Fabric of the Maritime Canadian Sandstone on Deterioration of Ornamental Bridges in Central Park, NYC

摘要

The sandstones from the Maritime Provinces in Canada, used for the construction and restoration of Bethesda Terrace and several ornamental arches and bridges inside Central Park, NYC, were known for their durability, consistency of weathering, variety of earth-toned colors, fine-grained composition and easy workability. Nonetheless, they display varying weathering behavior when exposed to the same environmental conditions. While the type and degree of deterioration of the stone noted by former researchers at Central Park have been attributed largely to extrinsic factors rather than intrinsic factors, the aim of this research is to understand how different forms of deterioration observed may relate to the sandstone’s mineralogy and texture and determine if weathering is dependent on the stone’s source and utilization. Mineralogical composition and textural characteristics are important in any study of stone deterioration and treatment performance. They are useful to understand stone performance and weathering when used with other materials in a structure with complex environment such as of New York City. For this study, the Maritime Canadian sandstones used inside Central Park are fully characterized by determining their mineralogical composition and textural characteristics using x-ray diffraction (XRD), polarized light microscopy (PLM), scanning electron microscopy (SEM) and methylene blue index (MBI) of clay. Hygric dilation measurements were carried out to measure the stress exerted during swelling when the expansion is constrained. This characterization helps to compare and contrast deteriorated, undeteriorated and new samples; see differences among sandstones from different quarries; and understand how a particular stone characteristic may influence the sandstone’s specific weathering behavior.