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Schmidt hammer pioneered nondestructive testing in construction industry

Non-destructive testing (NDT) is a number of different tests and measurements that can be performed to determine the properties of the tested structure. Trying to relate it to everyday activities we can say that picking tomatoes in a store is a perfect example of non-destructive testing, we evaluate their color, skin condition, size, weight, firmness, smell and if we have at least some experience we will probably be able to choose the tastiest, ripe tomatoes without tasting them.

The situation is similar in relation to the structural investigation. However, in this case, in order to obtain reliable test results it is necessary to have not only specialized knowledge but also appropriate equipment. Only such a combination allows to choose the right equipment and test methods for the given situation and then accurately analyze the results.

Sclerometric concrete test by swiss Proceq Type N Schmidt hammer
Schmidt hammer Type N measuring

It all started in 1948 when Swiss Ernst Schmidt invented and patented the first widely accepted instrument for testing the strength of concrete which today we call the Schmidt Hammer, Schmidt Sclerometer and in English also simply as the "Rebound Hammer", or "Swiss Hammer". Over the next few years, Ernst Schmidt and Antonio Brandestini, founder of Proceq and previously one of the three founders of BBR Network, developed and introduced the Schmidt Sclerometer into production and sales. The product has been a global success giving structural engineers unprecedented capabilities. Previously, rapid, non-destructive estimation of in-situ concrete uniformity and strength was simply not possible.

How does this device work? In a nutshell, it transfers the energy given to the plunger by the spring to the concrete surface and checks how strongly the plunger bounced off the tested surface - in fact, we measure the elasticity module, which is correlated with the strength of concrete. In practice, the construction of the device is slightly more complicated [see figure].

Type N Schmidt hammer internal construction
Schmidt hammer Type N construction

Like every invention, the Schmidt hammer initially raised doubts. Over the 60 years since its invention and introduction to production there have been thousands of publications, studies and standards regulating the method of sclerometric testing to determine the strength of concrete. Currently it is certainly the most popular and best described in scientific and standard sources method of non-destructive testing in construction. Standardization of Schmidt hammer testing has been undertaken by national standardization committees in, among others: United States (ASTM C 805), United Kingdom (BS 1881 part 202), Germany (DIN 1048 part 2). Also international ISO standards (ISO/DIS 8045) and European standards (ENV206 and EN 12 504-2) also raise the subject of the Schmidt hammer tests.

In Poland we had the PN-74/B-06262 Non-destructive testing of concrete structures. Sclerometric method. Compressive strength of concrete with the use of N-type Schmidt hammer, widely used was the ITB Instruction No. 210 Sclerometric method for strength testing of concrete in structures. Currently the standard PN-EN 12504-2 Concrete testing in structures - Part 2: Non-destructive testing - Determination of rebound number is in force.

For over 60 years, Schmidt's hammer has paved the way for non-destructive testing in construction to become widely known and used throughout the world.


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