RADAR IMAGING IN COMPOSITE MASONRY STRUCTURES

Masonry arch bridges represent a significant proportion of the UK bridge stock on both the roads and the railways. There are some 40,000 UK masonry arch road bridges and some 30,000 masonry arch rail bridges. If these bridges were taken out of service then both the UK road and rail networks would be completely inoperable. In order to aid the load carrying capacity analysis of these bridges, a series of NDT techniques have been developed at the University of Edinburgh, primarily focused upon masonry structures. As part of this ongoing programme a laboratory study of radar propagation through masonry has been undertaken. A 2.4 m long x 1 m wide x 1.5 m high experimental test rig was built in the laboratory with brick walls on three sides and a wooden gate on the fourth narrow side. Radar tests were undertaken using 500, 900 and 1000 MHz bow-tie antennae with the box filled with fresh water and then saline water with different concentrations of sodium chloride. Further tests were undertaken with the box filled with dry sand and wet sand. Finally the test rig was modified to simulate a composite masonry structure and tests were performed both on the hollow and sand filled model. The results from this work are reported herein indicating the reliability and ease of identifying various targets. It was found that radar signals were severely attenuated when the saline concentmtion exceeded 0.05%. Better results were obtained when the box was filled with dry sand rather than wet sand. In the case of the hollow cellular structure, refraction effects were more evident. For the covering abstract see ITRD E111699.