Discover the benefits, drawbacks and process of estimating the compressive strength of concrete using the SONREB method

What is SONREB?

SONREB is a compressive strength testing method for concrete. The term SONREB is a combination of sonic and rebound testing. It is a method of combining ultrasonic pulse velocity (UPV) with rebound hammer measurements.

What are the benefits for compressive strength testing of concrete?

The underlying concept of the combined method is that if the two methods are influenced in different ways by the same factor, their combined use could result in a cancelling effect that improves the accuracy of the estimated strength – Rilem TC-ISC

For example, if we have increased moisture content, the UPV value increases and the rebound value decreases. 

The idea behind the technique is to use two methods that are influenced in different ways by the same factor. This helps to provide a more accurate estimate of the compressive strength. 

This is what the EN13791 standard has to say about SONREB:

“The combined use of both UPV and rebound hammer techniques with core strength is a useful technique, but the procedures are not detailed in this document.”

There are some countries such as Italy and China for example where the SONREB method is very well known and there are national guidelines for it.

To see the real benefits, let’s look at the coefficient data from the rebound hammer alone, the UPV testing alone, and then both rebound + UPV together….

Above is a correlation made using the rebound hammer alone. As you can see the coefficient of determination is around 86%.

Using the UPV alone, we have a bit more dispersion. The coefficient of determination is 72%.

Now when we combine the two using the SONREB regression we get a 94% coefficient of determination. Clearly an impressive result.

What is the drawback of the SONREB method?

The drawback of using SONREB is that it requires more effort on site, particularly for the UPV measurement on site which requires the grid alignment and two people to do the test.

How to reduce onsite efforts with SONREB?

It is possible to reduce the onsite effort by using the Schmidt rebound hammer alongside pulse echo technology (UPE). Since 2021, this technique has been included in the European standard as an alternative to classical UPV measurement.

UPV determination using ultrasonic pulse echo

Let’s look at how to use pulse echo technology to determine ultrasonic pulse velocity. 

Classical UPV measurements typically measure the P-wave or longitudinal velocity. Pulse echo technology measures the S-wave or shear wave velocity. Either can be used for a correlation to compressive strength, or for simply analysing quality variations. The P- and S-wave velocities are related by the Poisson’s ration of the material, so it is possible to convert from one to the other.

SONREB procedure The SONREB procedure is quite simple. At each test location we need to measure the rebound value and the pulse velocity.

Then we determine the core strength at the same test location. We will repeat this at sufficient locations then use excel to generate the coefficients.

Finally, we can use a spreadsheet function to generate the correlation curve. You can find detailed guidelines on how to do this in this informative video with David Corbett.

For your convenience, you can download a pre-made spreadsheet from the Screening Eagle website which does this for you like the example below.

Comparing classical UPV with UPE

If we compare classical UPV with the pulse echo method, you will see that there are several practical advantages when it comes to on-site testing.

Most importantly, it only requires access from a single side. Ultrasonic pulse echo also requires no couplant.

Conclusion

SONREB significantly enhances concrete compressive strength estimation accuracy over single-method testing. While traditional UPV demands resources, pulse echo (UPE) simplifies the on-site application. This efficiency, coupled with improved precision, positions SONREB with UPE as a highly valuable tool for concrete assessment.

Learn more about concrete compressive strength assessment in our dedicated playlist on YouTube.