Title: Interpretation of Radar Test Results
Author(s): Stephen G. Millard, John H. Bungey,
Marcus R. Shaw, Cledwyn Thomas,
and Brian A. Austin
Publication: Symposium Paper
Appears on pages(s): 1-24
Keywords: concretes; conductivity; microwaves; nondestructive tests
Experimental work has been undertaken in the laboratory and on site to assist understanding and interpretation of the results of radar testing of structural concrete. This has included the development and use of a large-scale emulsion simulation tank in which a very large range of reinforcing steel and void configurations have been examined with field testing apparatus for a range of simulated concrete properties. A library of characteristic responses as well as limits of size and spacing upon successful resolution have been obtained. A large diameter co-axial transmission line has also been designed, fabricated and used to determine the fundamental electrical properties of a range of concretes and moisture conditions at frequencies from 1 MHz up to 1 GHz. Results have been compared with those for tests on larger concrete specimens with field testing apparatus and confirm the dominant influence of moisture compared with other aspects of the concrete composition. Frequency effects are quantified and related to characteristics of field antennas, and potential errors of using ‘typical’ values of concrete properties in interpretation and numerical modelling are identified. The test results from transmission line studies are compared with experimental and theoretical results from other research workers.