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Ground Radar Provides NDT Assessment of NZ Concrete Structures Print
Whilst traditionally surveyed via simple technologies with very limited imaging data being available as a result, rebar, post-tensioning cables, and other pipes/services integrated into concrete structures can now be imaged clearly, quickly, and flexibly using the technology of ground penetrating radar (“GPR”).

Limited applications of this technology to the imaging of concrete have been in service in NZ for some 4 years, one such application being jointly pioneered by Fulton Hogan Auckland and LORD Civil Christchurch was the quality control process in bridge beam manufacture.

Primarily, the innovations that have resulted in the technology now being so impressively suited to the above task has been the convergence of a suitable field platform for the GPR that offered minimal operational complexity, and companion proprietary software to permit on-site processing and image enhancement capable of displaying the rebar and imaged targets in real time, in excellent clarity, and in a choice of 2D/3D formats.

Applications are many and varied. Amongst the most pressing demanded by the Industry presently are the imaging of rebar in older concrete structures ranging from hydrology-related (e.g.: major concrete water reticulation storage tanks), rebar imaging in masonry or concrete buildings through to 1970’s vintage as an essential part of the requirements under the Building Act 2006 to ensure enhanced earthquake compliance, to older bridges and motorway structures for similar reasons.

A New Plymouth-based contractor, Detect Services Ltd, has commenced offering a national contracted service to the NZ Civil Industry of rebar imaging using this technology.

Another major area of the work undertaken by Detect includes assisting the avoidance of rebar during concrete cutting, the equipment even having the ability to image live electrical conductors and to overly dimensioned hole templates on imaged rebar so as to ensure that holes cut are re-positioned to minimise structural damage in the process.

Quality control of work done is also possible by use of this technology, providing a valuable and compellingly cost-effective means to correlate as-built work with that planned or permitted.

Formal reports are also offered to assist in the preparation of a fuller engineering report.

Equipment used is the latest such technology on the international market and is sourced from a Canadian maker. Employing a low-power 1000 mega-Hertz signal from a compact survey head with integrated odometer, the equipment is safe and non-destructive to use.

Commenting on some illustrative examples of work done to date, Detect’s CEO, Mr Graham Mist, is effusive. “The work for this equipment is hugely varied”, he reflects. “We have studied everything from a Northland bridge to identify rebar positioning prior to installing additional reinforcing rods as part of a strengthening job, to a 1920’s Hamilton building for seismic stability and reinforcing quality in preparation for the adding of another storey, a 1953 brick primary school bell tower in order to confirm reinforcing prior to a consultant designing a seismic reinforcing scheme for it, and the verification for permit issue purposes that a new concrete floor extension had been prepared and reinforced to code”.

Demand for the service is already strong and expected to become one of the faster-growing civil industry service areas in New Zealand over the next 18 months.

(Phone Detect Services +64 6 751 1126)
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