Crack Depth Determination
GPR is commonly used to determine areas of cracking e.g. in historical buildings, particularly where these are located in earthquake zones. Traditional antennas are used for this application. At the request of the UK Transport Research Laboratory, UtEl has developed specialised crack detection measurement tools. Rather than simply detecting the existence of cracking, these are optimised to measure the depth of cracking. This was originally used for top down cracking in flexible pavement (Highways) where the depth of the cracks rather than their extent on the surface determines the need for repair.
The image below illustrates the difference between using the crack detection antenna (cdh) and a traditional antenna to determine crack depth. The cdh reliably locates the crack and indicates both the top and the bottom. Comparison of the depths will give the depth to which top down cracking has permeated.
The image below is from a paper presented to GPR 2004 showing the comparison of the results of coring and using the crack depth detection head.
There are a number of publications showing the performance of the crack detector head. Please contact us if you would like more information.
Airports
For the repair and maintenance of airport runways and taxi areas, structural engineers need to know where subsurface cracking has developed below the tarmac surface. Top down cracking is visible on inspection but traditionally coring has been used to determine how extensive is the bottom up cracking i.e. the cracks which start at joints in the concrete and permeate up into the asphalt above. The cdh is a much more reliable tool for locating the joints in the concrete than a traditional antenna and it can also detect cracks which have developed at the joint but not yet reached the surface of the asphalt. “Traffic Light” reporting can then be used to indicate joints where cracking has not developed (green) or where there are subsurface cracks (red) or other anomalous indications (amber). An example of a good joint and one which has developed a crack into the asphalt above is shown below (with thanks to Atlas Geophyiscal for permission to use this data).
