プレストレストコンクリートの劣化診断を指向したセメント系積層材料の電気化学的特性の周波数依存性に関する基礎的検討

抄録

 In late years, poor grout filling and steel bar corrosion are the major issues of prestressed concrete structures. Hence, a practical use technology to detect these defects are demanded. Particularly, there are many unsolved problems about the nondestructive detection of the steel bar corrosion covered with sheath pipe.
 The goal of the research is a development of an electrochemical technique which enables to detect these defects from the surface of the prestressed concrete nondestructively.
 Analyses of multilayer substances utilizing electrochemical frequency response of materials caused by dielectric dispersion are carried out widely in various fields. For example, measurements of frequency response (AC impedance method) of reinforcing rod are mainly performed for corrosion diagnosis in the civil engineering and construction. Dielectric relaxation measurement applied to this research is one of the electrochemical techniques to estimate the internal microstructure of materials by analysis of electric charge behavior which causes polarization. Shape analysis of human body cell using dielectric relaxation technique are well known in the medical fields. The dielectric relaxation indices, such as electric capacitance and conductance relate to the quantity of reaction activated by electric charges. Furthermore, the change rate of indices according to frequency changing reflect increments of the reactions that are activated at each frequency. Large electric polarization will occur in low-frequency range because electric charges can reach the edge of materials and form capacitors. Accordingly, the measurement system behaves like a large capacitance double layer capacitor. In contrast, a direction of electric field changes extremely fast at the high-frequency range and electric sensitivity charges vibrate to positive and negative with small amplitude without being able to shift a long distance. The electric capacity becomes small when the system cannot be greatly polarized. The vibrations of electric sensitivity charges are observed as big conductance because electric charges are always trying to move toward positive or negative at high measurement frequency range.
 Authors conducted some dielectric relaxation experiments which relate to measurement repeatability, a variety of the electrodes, applied voltage magnitude, and materials configuration of specimens and results were obtained as below.
 1. Conductance requires close attention about its repeatability.
 2. A variety of the electrodes and applied voltage magnitude have influences on the characteristics of lower frequency behavior of capacitance and conductance.
 3. Behaviors of polarization charges reflect the specimen configuration and shape.