Concrete Strength Testing

The strength of concrete is an important parameter. However, testing the strength of concrete is not so straight forward. For a new construction, you can pour concrete cylinders or cube samples and cure them, if you have an existing structure, you can extract core samples. Thereafter you destructively crush-test a series of those samples in a testing machine. Using statistical methods, you can then determine the characteristic strength of the concrete, which for cast concrete is a value where, for example according to EN 206, 95% of the test values need to be above this characteristic strength value.

Yes, you are right, testing the strength of the concrete is not that straight-forward and is pretty costly. Furthermore, concrete is never uniform and, if you take samples while pouring concrete, these samples are not placed, compacted or cured similar to the concrete placed in the real structure. Meanwhile core samples from an existing structure are disturbed during the extraction process. All of these factors affect the estimated strength value. As you can see, there is no such thing as the one true concrete strength value, but it is a statistical method. But don’t worry - for a design, additional safety or resistance factors are applied to the destructively tested characteristic strength values mentioned. Overall, a pretty safe and conservative approach.

Are there other methods that can reduce the number of destructive tests or even eliminate them completely?

Yes, there are - and this is where our Schmidt Rebound Hammers for the estimation of concrete strength and uniformity come into play. We invented the Schmidt principle over 60 years ago and the method is completely non-destructive. Original Schmidt Live relies on mechanical principles to measure the rebound of a plunger hitting the concrete surface and for the Silver Schmidt Live it is an optical principle that measures the rebound of the plunger. This rebound value can then be translated into concrete strength using various correlation curves. According to many international standards you can correlate our Schmidt Live rebound values with the statistical values from crush testing and, with this, reduce the number of expensive and time-consuming destructive tests. It is great to be able to save money for your customer while delivering even more reliable results.

As with obtaining the result from crush tests, the rebound method is also statistical. Nope, there is really no excuse for not using the Schmidt Live because, if done correctly, it gives you more reliable, more holistic and much more cost-effective concrete strength estimation when combined with a few crush tests. Now, for those really advanced users, based on the latest international standards, and to determine a conforming compressive strength class of the concrete, you can even eliminate all destructive core samples and only use the Schmidt Live. How efficient is that!?

So, what is unique about the Schmidt Live family?

 1.     It enables an entirely digital workflow that can easily be done by a single person. Each rebound value is displayed on the hammer including a quick statistical evaluation. All the conversions from the rebound value to concrete strength according to the selected standards or based on your own conversion curves are done on a mobile application. This also includes one-click reporting - and why not add some pictures of the tested object to the report as well? What takes days for crush tests, hours with an analogue hammer, now only takes minutes with the Schmidt Live.

2.     When it comes to which hammer to use, it is clearly the Silver Schmidt Live, because it covers a wider range of concrete strengths - thanks to the optical method it has reduced wear and due to its patented mythology is extremely accurate. If you have always been used the Original Schmidt and feel comfortable with the R value, the Original Schmidt Live certainly does an excellent job in full compliance to standards and it has all the digital benefits as well.

Interested? Let’s organize a video call with our sales team, because a personal conversation is just so much better than those old-fashioned brochures. Let us show you how to boost your productivity and accuracy in concrete strength and uniformity testing. You can find more information here and don’t forget to ‘like’ this article

Talk soon, and together - we can protect the built world.