Validation of NDT-methods

Division 8.2 Non-destructive Damage Assessment and Environmental Testing Methods investigates and develops non-destructive testing methods in civil-engineering (NDT-CE) to handle practical testing problems. The applications of the testing methods contribute to give a statement of the security of buildings and their durability.

Only a few standards for a special applications of NDT-CE methods are available. Due to that fact validation has to proof if and how far a testing method is suitable to meet the requirements of a specified testing problem. These requirements relate to well known practical testing problems (e.g. thickness measurement, detection of content from damaging salts), questions handled in official expertise or requests at BAM. Within the consulting and information BAM supports customers to establish a concept for a validation.

BAM has a range of specimens from different materials, properties and dimension at disposal. Furthermore several NDT-CE methods representing the state-of-the-art are under permanent use. So validation problems within investigation, construction process or quality control can be processed in accordance with the customers needs.

The effort of a validation process relates to the importance of a testing problem and the level of security as well as the claimed reliability.

The principle approach in a validation process contains two main steps:

1. Determination of parameters under well defined conditions
2. Conclusion that the testing method is suitable to meet the specified demands of the customer within a test procedure.

Reference test specimens have to be established using varying materials, properties and geometry. Well-defined voids and devices with certain properties (tendon ducts with grouting faults, areas with different bonding conditions) must be implemented. Therefore the large concrete specimen and a wall built with historical brickwork are available at the BAM site. With these reference specimens tests will be performed investigating the change of the results varying different parameters.

Besides method comparison of different NDT-CE methods gained results will be verified by reference testing methods (e.g. radiography). Furthermore systematic, subjective and coincidental influence are investigated and their effect on the gained results. Reproducibility, comparability and sensitivity as well as the limit of detection will be considered in the validation process.

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