THE INFLUENCE OF CONCRETE COMPOSITION UPON RADAR TEST-RESULTS

Interpretation of radar investigations of concrete structures is hampe red by uncertainties about the relative permittivity and conductivity of the in situ concrete. A co-axial transmission line system has been designed and developed to enable both of these parameters to be derive d from measurements over a frequency range from 1 MHz to 1 GHz, which encompasses the frequencies associated with commonly used field-testin g apparatus. This facility permits removal of concrete laboratory samp les from the transmission line for curing and conditioning, and has be en used to examine a range of concrete mixes. These have incorporated different strength levels, aggregate types and sizes, cement replaceme nts and contaminants, with moisture contents ranging from saturated to oven-dry. The influence of hydration upon tests at early age has also been considered, together with the relationship between results measu red at discrete frequencies and those evaluated using broadband antenn as.