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Test of experience The importance of engineering expertise should not be underestimated despite advances in concrete testing appliances, according to some leading consultants. Mike Walter reports.

Non-destructive testing equipment is increasingly being used to analyse the integrity of concrete structures in preference to more traditional techniques like core sampling, for a variety of reasons.

The success of techniques such as radiography and thermography is partly down to the fact that they remove the need to bore into structures to identify failing concrete, measure cover to reinforcement and locate voids within concrete. Radiography and thermography equipment is hailed by the manufacturers as being easier to use, with an added benefit of instant results relayed to the operator on handheld monitoring apparatus.

Despite the apparent simplicity of concrete testing, consultants say this does not remove the need for competent engineers to be employed to operate the equipment. Correct analysis of results can, in their opinion only be achieved by trained personnel who can properly diagnose problems and recommend further concrete analysis which may be required.

George Ballard, director of consultant GBG, says: 'The most important aspect of the job is the person who operates the machine. You should never give up on the professional expertise of engineers. Quite often the perception from a manufacturer's point of view is that the equipment can do everything, removing the human skill factor.'

Ampthill Geophysical Consulting's partner Tim Scull agrees: 'You still need experienced people to operate the equipment and to initially interpret results. While the clarity of the results is getting better and the computer read outs are becoming more useful, you need to know what you are looking for before the results are passed to the laboratory.'

Destructive methods of sampling concrete such as fracture testing and core sampling are still regarded as valuable methods of further investigation. For initial investigation destructive techniques are being preceded by non-destructive alternatives because the latter do not usually rely only on samples taken from various points on a structure.

'The main benefit of non-destructive testing is that it can be used to sample the whole area of a concrete face at once rather than just at one point - making the results less random and helping to identify problem areas more quickly,' says Scull.

Non-destructive equipment supplier Hammond Concrete Services says that the new apparatus comes into its own if the client wants to limit expenditure. Director Michael Owen says: 'There are tremendous savings to be had with the new equipment as it only takes a fraction of the time to operate. For example, establishing where steel bars are in a large reinforced concrete structure could take two weeks with penetrative methods, now the data can be gathered in one day using radiography.'

Impulse radar and moisture testing are two techniques where the equipment is becoming lighter and more portable. Impulse radar involves transmitting and receiving pulses of radio waves in a structure using an antenna passed over the surface. Voids or steel features hidden within the concrete give off different electrical signals which are relayed back to the operator.

Moisture testing can be used to determine the dryness of solid concrete floors, an important factor as moisture in solid floors can cause floor failure. The operator places a hand-held tester on the floor which gives automatic readings of the water content in the concrete at varying depths.

Manufacturers claim that such monitoring equipment helps to identify more easily where a problem lies. 'The need for evidence when a concrete bridge or tunnel is alleged to be unsafe is paramount so the client can properly take action,' says Owen.

One of the very latest pieces of equipment used for concrete testing is thermography. Thermal imaging cameras are positioned at a structure to pick up precise surface temperature discrepancies, revealing minute changes in heat flow caused by hidden changes in the concrete's structure or condition.

The method can check for delamination in reinforced concrete bridge decks, examine heritage buildings for internal voids or cracks and assess new build structures for concrete cover.

Such information is vital in assessing the integrity of concrete, but the onus is on the client who may be unsure as to which testing technique to employ, or if any should be used at all.

Manufacturers and consultants alike stress the importance of planning ahead before waiting for signs of concrete failure.

'There used to be an enormous resistance by the client to look ahead, which is still often the case, but the engineering profession is getting better at checking structures before problems show,' says George Ballard of GBG.

Aperio's geophysical consultant Rod Eddies sees the new-build market using the equip- ment more, checking for defects before a contract is handed over. 'This sort of equipment used to be called in when things went wrong. Now such tests are often being specified in the design of a structure.

'The market has become very buoyant recently. Engineers are becoming more confident and aware of the techniques available,' said Eddies.

Mike Walter writes for Barrett Byrd Associates

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