|
|
|
Surface Weathering Degree Mapping for Granite Using Reflectance Spectroscopy
Chang-Uk Hyun
Department of Civil, Urban and Geosystem Engineering, Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
hyuncu99@snu.ac.kr
Hyeong-Dong Park
Department of Civil, Urban and Geosystem Engineering, Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
hpark@snu.ac.kr
Abstract
Combinations of reflectance spectroscopy and various constituents matching algorithms have been successfully used to classify and to detect geomaterials in field of remote sensing. Measuring reflectance spectra on the rock surface can be applied to assess degradation of rock surface as a new non-destructive inspection method. In this paper the spectral reflectances of weathered granite specimens of Mt. Gwanak were measured by using field spectrometer and spectral characteristics of reference minerals were used to identify rock-forming minerals of the granite from the spectral reflectances obtained using field spectrometer. Granite is mainly composed of quartz, feldspar and mica. Hardness and durability of quartz are greater than other granite forming minerals and quartz has no diagnostic peak in spectral reflectance curves, but feldspar and mica produce clay minerals, such as illite and kaolinite, according to weathering processes. Thus comparison of the amount of the clay minerals using absorption peak in the spectral reflectance curves among differently weathered granite specimens could result in newly designed weathering indices against rock surface mineral composition.
1. Introduction
In civil engineering, rocks are used for building materials and foundation of construction, so its engineering properties and physical characteristics are critical for concrete construction. Weathering changes physical characteristics of rocks, such as strength, hardness and durability, or texture and color on the surface which are important for conservation of stone monument and exterior of the building.
To assess weathering degree of rocks various techniques and methods have been used. Qualitative assessments using naked eye of geologist and chemical analyses of rock-forming mineral composition have been commonly used to assess rock deterioration. But chemical analyses are time-consuming and damage objects. The assessments by geologist have limits to produce subjective and qualitative results.
Reflectance spectroscopy is non-destructive and makes fast investigation on the rock surface. Spectra measured using spectrometer on the rock surface make researcher quantitative interpretation about weathering degree. In this paper we investigated weathering processes of granite forming minerals and measured reflectance curves on the weathered granite specimens of Mt. Gwanak in Korea. By using absorption features of the spectra weathering degree of specimens could be compared.
|
|
|