Non-Destructive Concrete Testing

Not meeting strengths? It may not happen today or tomorrow, but chances are at some point in time your concrete or cementitious repair may not reach the design compressive within the target date. What if the material has already set or has been hydrating for a week? Usually coring is not an option and replacement is a last resort. So, what are the other options?

Non-destructive testing is a great place to start a low-strength investigation for an in-place concrete structure. One of the simplest and most readily available forms of non-destructive testing is with a device known as a rebound hammer, also referred to as a Schmidt or Swiss hammer.

A rebound hammer is a spring-loaded, hand-held device that is used to obtain compressive strength data for already hardened concrete or other cementitious structures. The device is easy to use, and you can obtain an in-place compressive strength estimates in minutes. Conversions are completed by referencing a conversion chart typically tagged in metal to the device itself. Digital rebound hammers are also available which are more costly; however, they will convert automatically.

If you don't have immediate access to a rebound hammer your local ready-mix supplier should. Ensure that the rebound hammer has been calibrated within the year and testing practices are in compliance with ASTM C 805. Hopefully the material in question is found to be structurally sound, and the investigating ends shortly after rebound testing is performed.

When considering non-destructive testing, be sure to ask the question, "what is the function of the structure in question?" This will help determine the magnitude and precision of testing necessary. The answer will provide a platform for discussion in determining the appropriate testing needs. There must be a proper diagnosis prior to rehabilitation. It is not economical to spend thousands of dollars on testing if the tests do not supply the data you need.

For example, the rebound hammer is not sufficient for every investigation; however, it is a good starting point. The rebound hammer is 70-80% accurate when testing lab specimens and slightly less accurate when estimating in situ structures.

Everything has its place, including test methods; ASTM and other governing specification institutes exist because testing has to be specific. Should an investigation require additional test data, there are alternative methods of non-destructive testing to consider. These include The Windsor Probe, ultrasonic testing, rebar locators, corrosion testing, bond testing, moisture testing and anchor testing.