An Overview of Concrete Strength Testing Methods

Compressive strength of concrete may be defined as its load withstanding ability before failure. This is one of the most important parameters for the performance of concrete, and provides a clear idea about the integrity of any concrete structure.  

Many different methodologies are used for concrete strength testing. While choosing a testing method, the impact of these techniques on their schedule is taken into account by the project managers.  Some of these methods can be performed directly onsite whereas some others need additional time for delivery of strength data by third-party facilities. Apart from time, accuracy of the process is also considered because it has a direct impact on the quality of the concrete structure. 

Some of the most common testing techniques are discussed below.  

Rebound Hammer or Schmidt Hammer: 

This method utilises a spring release mechanism for activating a hammer. Under the impact of this hammer, a plunger gets driven into the concrete surface. Values from 10 to 100 are assigned to the rebound distance between the concrete surface and the hammer. The strength of the concrete is then correlated to this measurement.  

This method is quite uncomplicated and can be performed onsite. However, the test results can be skewed by the presence of large aggregates and surface conditions. Also, to ensure accuracy of measurements, pre-calibration is required using cored samples.  

Ultrasonic Pulse Velocity: 

The velocity of a vibrational energy pulse is determined in this method through a slab. A measure of the concrete’s elasticity, density, and resistance to stress and deformation is provided by the ease with which energy travels through the slab. This non-destructive testing technique can also detect flaws such as honeycombing and cracks.  The presence of moisture in the concrete element, aggregates, and reinforcements can influence this technique.  

Penetration Resistance Test: 

This testing technique involves driving a probe or small pin into the concrete surface using a device. Concrete strength is correlated here to the depth of the hole and the force required for penetrating the surface.   

Though this simple technique can be performed onsite, data can be impacted significantly by surface conditions, aggregates used, and the type of form.  

Pullout Test: 

This test uses a post-installed or cast-in-place metal rod to pull the concrete. A measure of concrete’s compressive strength is provided by the force required to pull the concrete and the pulled conical shape.  

This method can be applied to new as well as old concrete structures. However, it damages or crushes the concrete and requires large number of test samples to deliver accurate results.  

Drilled Core:  

This test involves extraction of hardened concrete from a slab using a core drill.  In-situ concrete strength is monitored by compressing these samples in a machine.  

Compared to field-cured specimens, these samples are more accurate. However, this destructive technique damages the slab’s structural integrity and core locations need to be repaired later.   

Coating Management Solutions (CMS) is one of Australia’s most trusted names in inspection and assessment of concrete structures. To find out more about concrete strength evaluation, please contact our concrete structure specialists today.