Non-destructive testing of bridge, highway and airport pavements

In the inspection of metals and metal-based materials nondestructive testing is an accepted practice. For example, radiographic and ultrasonic techniques are routinely used to identify anomalies in steel pipelines and there are recognized national and international standards on their use. However, in the inspection of concrete the use of nondestructive testing is relatively new. The slow development of nondestructive testing techniques for concrete is because, unlike steel, concrete is highly non-homogeneous composite material. Apart from precast concrete units, which like steel products, are fabricated at a plant, most concrete is produced in ready-mixed plants and delivered to the construction site. The placing, consolidation and curing of concrete takes place in the field using labor which is relatively unskilled. The resulting product is, by its very nature and construction method, highly variable and does not lend itself to testing by nondestructive methods as easily as steel products.