Concrete Hammer Test: A Complete Guide [Updated 2024]

The concrete hammer test is useful for determining a variety of concrete characteristics in a non-destructive way. With it, a technician can assess the uniformity and quality of the concrete based on standard specifications, compare the quality of concrete elements and establish a relative strength profile for a concrete structure. Each of these results can be determined using the same simple tool: a concrete test hammer.

How to Perform the Concrete Hammer Test

Performing a concrete hammer test is relatively simple. You simply hold the concrete test hammer (AKA, impact hammer or rebound hammer) of your choice against the concrete structure and release the spring-loaded hammer. Generally, the hammer tool will have a digital window and scale along the side where you can view the rebound value from the hammer’s impact.

Steps for Performing the Concrete Hammer Test

Use a Schmidt hammer calibration anvil to check the calibration of your test hammer after every 1,000-2,000 impacts. You should also test your hammer before each use.
Make sure the concrete surface you will be testing is smooth, clean and dry.
If the surface is not smooth, use a concrete grinding stone to prepare it for the hammer test.
Your chosen impact point should be at least 20mm away from the edge of the structure or any shape discontinuities.
Take six rebound readings at each site and determine the average for a reliable value.

It’s also important to keep in mind that the types of aggregate and cement used to create concrete can influence the results of a concrete hammer test. Therefore, you will need to evaluate the results of the test based on the specifications of the mixture. Age, curing and carbonation of concrete can also affect the rebound number determined by your test hammer.

Pros & Cons of the Non-Destructive Concrete Testing

Like any materials testing procedure, the concrete hammer test has its strengths and weaknesses, and it shouldn’t be taken as an absolute measure of concrete’s compressive strength.

Pros

Use a Schmidt hammer calibration anvil to check the calibration of your test hammer after every 1,000-2,000 impacts. You should also test your hammer prior to each use.
Make sure the concrete surface you will be testing is smooth, clean and dry.
If the surface is not smooth, use a concrete grinding stone to prepare it for the hammer test.
Your chosen impact point should be at least 20mm away from the edge of the structure or any shape discontinuities.
Take six rebound readings at each site and determine the average for a reliable value.

Cons

The results are based on a local point and aren’t a complete indicator of concrete’s compressive strength.
Other flaws in the concrete’s structure cannot be detected using only this test.
The areas you test must be carefully selected and prepared.

When used within its capabilities, the concrete hammer test is easy to perform, reliable and applicable to any structure, since it isn’t destructive.

A calibration anvil and a grinding stone are important to have on hand when preparing to perform the concrete hammer test. But, when it comes to the test itself, all you need is the hammer! There are a few main types of concrete test hammers to choose from:

Schmidt Hammer Type N: Concrete test hammers are sometimes called Swiss Hammers or Schmidt Hammers, and this is where the name comes from. Schmidt Hammers can be used for a wide variety of non-destructive concrete tests. The Type N is ideal for concrete strengths ranging from 1,400-10,000psi.
Schmidt NR Hammer: The NR Hammer is also ideal for concrete strengths ranging from 1,400-10,000psi. However, the NR has the added capability of automatically recording rebound numbers as a bar chart on a paper strip for quick and easy comparison. Each strip chart can log up to 4,000 impacts.
Gilson Type N Hammer: The Gilson Type N can test concrete strength within the same range as the Schmidt Type N. This test hammer can also be used to estimate how much damage a concrete structure has taken due to freezing or fire. It also comes at a slightly lower price point.

Choose Your Concrete Hammer Test Equipment at Certified MTP

The Concrete Hammer Test, also known as the Schmidt Hammer Test or rebound hammer test, is a non-destructive testing method widely used in the construction industry to assess the compressive strength of concrete structures. Invented by Ernst Schmidt in 1948, this test offers a quick, economical, and easy-to-use tool for onsite evaluation of concrete strength.

Principle and Equipment:

The test operates on the principle of measuring the rebound of a spring-loaded mass impacting against the concrete surface. The equipment, commonly known as a Schmidt hammer, consists of a spring mechanism within a tubular housing. When released, the spring drives a mass to hit the concrete surface, and the rebound distance of the mass is measured on a scale. This rebound distance, which is a measure of the surface hardness, is then correlated to the concrete’s compressive strength.

Procedure:

To perform the test, the surface of the concrete is first smoothed and cleaned to remove any loose material. The hammer is held perpendicular to the surface, and the test is carried out by pressing it against the concrete. A typical test involves taking multiple readings at various points on the surface to obtain a comprehensive assessment. The average of these readings is then used to estimate the concrete’s compressive strength.

Applications:

The Concrete Hammer Test is ideal for assessing the uniformity of concrete, detecting weak spots in the structure, and estimating the strength of existing concrete structures. It’s often used in bridge inspections, building evaluations, and quality control of new construction. However, it’s important to note that the test only provides an estimation of strength and should be supplemented with core testing for a more comprehensive analysis.

Advantages and Limitations:

The primary advantages of the Concrete Hammer Test are its speed, ease of use, and non-destructive nature. However, it also has limitations, including sensitivity to surface conditions and the need for calibration against known concrete strengths. The test is best used as a comparative tool rather than a definitive measurement of strength.

In conclusion, the Concrete Hammer Test is a valuable tool in the field of construction, providing quick and useful insights into the quality and strength of concrete structures.