Rebound Hammer Test (Schmidt Hammer)

The rebound hammer test — also known as the Schmidt hammer test — is a rapid, non-destructive method for assessing the surface hardness of hardened concrete and estimating its compressive strength. A spring-loaded mass strikes the concrete surface through a plunger; the rebound distance is measured and converted to a rebound number, which correlates to compressive strength via calibration curves.

The rebound hammer is ideal for uniformity mapping across large structures, comparative assessment between concrete elements, and preliminary strength estimation when non-destructive assessment is required.

Test Standards We Follow

When Is Rebound Hammer Testing Used?

• Uniformity assessment across large structures

  Map surface hardness across walls, columns, slabs, and beams to identify areas of inconsistent strength.

• Comparative strength evaluation between pours

  Compare the relative strength of concrete from different pours or between structural elements.

• Investigation of concrete suspected of being under-strength

  Follow up on failed cube results with in-situ non-destructive assessment before deciding on further action.

• Screening prior to more definitive tests

  Identify areas requiring more detailed investigation via UPV or core extraction.

• Assessment of existing buildings

  Evaluate concrete condition before renovation, change of use, or structural modification.

• Bridge and infrastructure condition monitoring

  Periodic checks on bridges, viaducts, and other infrastructure to detect deterioration over time.

• Forensic investigation following incidents

  Assess concrete affected by fire, impact damage, or environmental exposure.

How the Test Works

• Step 1 — Surface Preparation

  The test surface is ground smooth using a carborundum stone over an area of approximately 150 by 150 millimetres to remove surface irregularities, plaster, or coatings.

• Step 2 — Instrument Verification

  The rebound hammer is verified against a calibration anvil before use to confirm consistent performance.

• Step 3 — Position and Orientation

  The hammer is held perpendicular to the test surface. Orientation (horizontal, vertical up, vertical down, angled) is recorded and applied to the correction factor.

• Step 4 — Impact Readings

  A minimum of 10 rebound readings are taken within the test area, with each impact point at least 25 millimetres from any edge or another impact point.

• Step 5 — Data Processing

  Outliers are discarded per the standard, and the mean rebound number is calculated for each test location.

• Step 6 — Strength Estimation

  The rebound number is converted to estimated compressive strength using the manufacturer’s calibration curve or, ideally, a site-specific correlation established from cores.

Why Foundtest for Rebound Hammer Testing?

• Calibrated digital rebound hammers with traceable certificates

• Experienced technicians who interpret results in engineering context, not just raw numbers

• Field reports issued within 3 working days of testing

• Recommended follow-up testing advised where readings warrant investigation

• Combined packages available with UPV testing for enhanced reliability (SonReb method)

• Full compliance with BS EN, MS EN, and ASTM standards

Rebound Hammer Test FAQ

Is the rebound hammer test destructive?

No. It is a fully non-destructive test that leaves only a very small mark on the concrete surface. It is safe to use on completed structures, finished surfaces, and heritage buildings without causing damage.

How accurate is the compressive strength estimate?

The rebound hammer gives an estimate typically within plus or minus 20 percent of true compressive strength when properly calibrated. For definitive strength values, we recommend following up with core testing on selected locations.

Can rebound hammer testing replace cube tests?

No. It is a complement, not a replacement. Cube tests remain the primary quality control method for concrete during construction. The rebound hammer is used for in-situ assessment of hardened concrete already in place.

How many readings do you take at each location?

A minimum of 10 rebound readings per test location, as required by BS EN 12504-2, with statistical processing to remove outliers and calculate a reliable mean rebound number.

Can you test old concrete structures?

Yes — this is one of the most common applications. We regularly test buildings 20 years old and older to assess concrete condition before renovation, adaptive reuse, or structural modification.

Related Concrete Tests

• Cube Compressive Strength Test — primary quality control on fresh concrete
• Ultrasonic Pulse Velocity (UPV) Test — pairs with rebound hammer in the SonReb method
• Windsor Probe Test — semi-destructive penetration testing
• Concrete Core Test — definitive in-situ strength from extracted cores
• All Concrete Testing Services