ABSTRACT
Hardness methods of a number of different specifications are being widely used in all parts of the world in concrete practice today. A large amount of published work on the appreciation of the methods and their use in specific circumstances is available. A number of national standard organisations have produced standards, recommendations ([1] to [7]), or have given guidance on the use of hardness methods in concrete testing and in the interpretation of results. The RILEM NonDestructive Testing Committee have sampled expert opinions in a number of countries and have published their findings ([7], [8], [9]). The summary report on the survey concludes that the methods provide only an approximate indication of quality but that they are useful in a number of applications. We mention here the combination of hardness methods with other non-destructive methods in order to estimate concrete strength.
