MICROWAVE SUB-SURFACE IMAGING TECHNOLOGY FOR DAMAGE DETECTION OF CONCRETE STRUCTURES

Abstract eng:
Invisible damage such as voids and cracks inside concrete and debonding between rebars and concrete caused by corrosions and earthquakes are of significant concerns. In this study, a microwave sub-surface imaging technology using a bi-focusing operator has been developed in order to detect such internal voids/objects and to quantitatively assess their dimensions. The proposed imaging system consists 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 the transmitting and receiving fields. An imaging algorithm using a numerical focusing operator was developed, which allows the recovery of a 2-dimensional object from its scattered field. For the experimental verification, a prototype planar antenna array consisting of 64 transmitting and 64 receiving antennas was fabricated and tested on a concrete block. Internal and invisible voids in the block were successfully detected. The sub-surface imaging technology developed in this research for quantitative condition assessment of concrete structures will lead to improvement of the effectiveness and efficiency of the current visual-inspection-based maintenance.

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