Near-infrared fiber optic spectroscopy for civil engineering materials evaluation.

摘要

This dissertation is part of a research program focusing on development of optical sensing probes for in-situ and distributed measurements in the subsurface environment. The sensing system presented employs near-infrared molecular vibration spectroscopy using evanescent wave fiber optic probes. The evanescent wave is a surface wave that travels along the optical fiber at the boundary of the core and the fiber cladding. It is used to interrogate the environment immediately surrounding the fiber core.; Two types of probes were examined: (1) Bare core probes for method evaluation. They allow sampling of the analyte surrounding the fiber core; (2) Probes with permeable cladding for in-situ field applications. They function by interrogation of the analyte diffused through the permeable cladding. Partially hydrolyzed cellulose acetate and Nafion were investigated as possible cladding materials.; Measurements of liquid and gaseous water were carried using both the bare core and the permeable clad probes.; Measurements of sodium chloride in aqueous solutions were carried out using the bare core probes. Interference factors such as moisture content, changes in pH level, or temperature fluctuations were investigated. Methods for positive identification of sodium chloride are presented.; Ingress of water in mortar was monitored using embedded bare core probes. Results of desorption and capillary sorption are presented. Concrete samples containing embedded fiber optic probes were subjected to a standard accelerated chloride penetration test. The results indicate that the proposed system can be used to reveal internal variations of moisture and chlorides in cementitious materials.; Other applications of the proposed sensing system are also presented. Such applications include hydrocarbons and moisture measurements in the geo-environment and monitoring changes in pH level.