As a one time employee of Portsmouth City Council I read with interest the article on the landmark Spinnaker tower (NCE last week).
Before filling the tower up with resin, should not the extent of voiding be established? This could be achieved using a hand held radar antenna.
As the concrete inspector pulls the antenna across the profile line surface, the image could be interpreted in real time on the computer screen for voiding. The images from the recordings could also be analysed later.
It may be possible to produce 3D block views from radar traces taken at different positions. These could then be observed from a variety of viewpoints and ways in order to judge on the repair.
I used radar many years ago on a pedestrian tunnel which was partly below water level. It was leaking at one point and the survey found honeycombed concrete deep inside apparently sound concrete.
Andrew Smith, senior engineer, WSP Cantor Seinuk, Holborn, London EC1N 2HS