Importance and Need of Non-Destructive Testing

It is often necessary to test concrete structures after the concrete has hardened to determine whether the structure is suitable for its designed use. Ideally such testing should be done without damaging the concrete.

The tests available for testing concrete range from the completely non-destructive, where there is no damage to the concrete, through those where the concrete surface is slightly damaged, to partially destructive tests, such as core tests and pullout and pull off tests, where the surface has to be repaired after the test.

The range of properties that can be assessed using non-destructive tests and partially destructive tests is quite large and includes such fundamental parameters as density, elastic modulus and strength as well as surface hardness and surface absorption, and reinforcement location, size and distance from the surface. In some cases it is also possible to check the quality of workmanship and structural integrity by the ability to detect voids, cracking and delamination.

Non-destructive testing can be applied to both old and new structures. For new structures, the principal applications are likely to be for quality control or the resolution of doubts about the quality of materials or construction. The testing of existing structures is usually related to an assessment of structural integrity or adequacy. In either case, if destructive testing alone is used, for instance, by removing cores for compression testing, the cost of coring and testing may only allow a relatively small number of tests to be carried out on a large structure which may be misleading. Non-destructive testing can be used in those situations as a preliminary to subsequent coring.

Typical situations where non-destructive testing may be useful are, as follows:

• Quality control of pre-cast units or construction in situ
• Removing uncertainties about the acceptability of the material supplied owing to apparent non-compliance with specification
• Confirming or negating doubt concerning the workmanship involved in batching, mixing, placing, compacting or curing of concrete
• Monitoring of strength development in relation to formwork removal, cessation of curing, prestressing, load application or similar purpose
• Location and determination of the extent of cracks, voids, honeycombing and similar defects within a concrete structure
• Determining the concrete uniformity, possibly preliminary to core cutting, load testing or other more expensive or disruptive tests
• Determining the position, quantity or condition of reinforcement
• Increasing the confidence level of a smaller number of destructive tests
• Determining the extent of concrete variability in order to help in the selection of sample locations representative of the quality to be assessed
• Confirming or locating suspected deterioration of concrete resulting from such factors as overloading, fatigue, external or internal chemical attack or change, fire, explosion, environmental effects
• Assessing the potential durability of the concrete
• Monitoring long term changes in concrete properties
• Providing information for any proposed change of use of a structure for insurance or for change of ownership.