Impermeability control using multi-frequency GeoRadarelixandre
The roof the Galleries Lafayette has been inspected by Cementys
In February 2014, following a solicitation made by the group “Galleries Lafayette”, Cementys did a diagnosis campaign on the deck located on the 8th level of the store (synthetic grass) to control its impermeability. The method chose was the analysis of reflected electromagnetic waves, called GeoRadar auscultation.
A radar is a device capable of sending an electromagnetic pulse ; that pulse will then propagate inside the material with more or less losses. The differences in material property create interfaces which reflects a portion of the pulses’ energy. These reflections are captured and saved during a time span defined by the operator to create a radargram, a graph showing the amplitude of the returned signal against time.
The water content will have an influence on the effective permittivity of the concrete: it means that if the water content increases, its aptitude to be electrically polarized will also increase and therefor the dielectric constant will also rise. Overall, the changes in the electromagnetic reflectivity at the water-concrete interphase is due to the presence of water.
Thanks to this technology, Cementys was able to do a mapping of the impermeability and a diagnosis of the roof of the Galleries.
Example of a mapping showing impermeability problems (analysis done at the frontier concrete-waterproofing layer)
Example of a mapping showing no stagnating water (analysis done at the frontier concrete-waterproofing layer)