Microwave Sub-Surface Imaging of Damage in Concrete Structures

摘要

It has been well demonstrated that the structural performance of reinforced concrete (RC) columns can be enhanced by retrofitting using fiber reinforced polymer (FRP) composite jackets. Therefore, an increasingly large number of bridges and building columns have been retrofitted with such jackets. The authors developed a microwave imaging technology for detecting such damage as voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column. The authors developed surface imaging technology using focused microwave in previous works. In this paper, extending the earlier analytical and experimental works, a microwave subsurface imaging system using antenna array was developed and verified for its capabilities to assess the damage of concrete structures. The proposed imaging system uses an arrangement consisting of several cylindrical or planar arrayed antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. This paper describes a numerical focusing procedure and numerical simulations demonstrated that the sub-surface image can be successfully reconstructed by using the proposed subsurface imaging technology. For the experimental verification, the prototype of planar antenna array was fabricated and tested on the concrete block, in which the artificial voids were inserted.