M.R. Shaw

Dielectric properties of concrete and their influence on radar testing

Sub-surface radar is becoming increasingly popular as an inspection method. Interpretation can be enhanced if uncertainties about the dielectric properties of the concretes under investigation are removed. The need for reliable data to identify possible variations of the dielectric properties of different concrete mixes and their condition on site has led to a systematic laboratory based experimental programme under the auspices of a major European Commission (Brite-Euram III Framework 4) funded project. Some key results from this recently completed work are presented in this paper with practical implications related to field surveys of structural concrete.

Assessing bridge pier scour by radar

Detection of river-bed scour around bridge piers represents a major current problem for engineers both in the UK and internationally. Techniques using boat-mounted impulse radar survey equipment have been suggested as a potentially viable solution to the problem. A programme of systematic laboratory model tests has been undertaken to examine the influences of pier and hole geometry upon measured radar response. These tests have been supplemented by field trials on real scour holes. Results from both laboratory and field studies have been used to validate numerical models developed using ray-tracing and finite difference techniques.

The influence of reinforcing steel on radar surveys of concrete structures

Buried reinforcing steel is an important factor when considering the results of a survey of structural concrete with subsurface scanning pulsed radar apparatus. In some cases it may be desired to estimate the positions and sizes of bars, whilst in other cases detection of features below the level of bars located near to the surface may be required. The results of an experimental programme using a specially developed simulation tank modelling a concrete slab with a wide range of reinforcing steel configurations are reported. Results relate to 1 GHz test frequency, with bar size, spacing and depth as variables, together with concrete relative permittivity and electrical conductivity. The ability to detect individual bars within groups, and to assess bar size and cover, is examined. Recommendations are given for minimum acceptable spacings to avoid masking. These results are supplemented by tests on laboratory-cast concrete specimens and field trials on precast concrete wall panels of known depth and reinforcement configuration.