Concrete Investigation and Non-Destructive Testing (NDT)
When specifying a project, during construction or when assessing the condition of an existing structure, assumptions are often made about the quality of concrete. Where these assumptions are incorrect it can result in failures or extra cost.
We've teamed up with Beta Design Consultants to give an overview of the main types of on-site testing that can be carried out, to assist stakeholders in achieving a “right first time” approach.
A range of different tests can be used during or after the construction phase to investigate the condition of concrete and to predict future performance of the structure. Some tests are in-situ while others require samples for lab testing, some are intrusive while others are non-destructive.
It's important for project professionals to understand the purpose and limitations of each type of test to decide which ones are necessary for their project.
Below are 3 of the most common tests performed.
Rebound (Schmidt) Hammer Test
Why is it used?
The Rebound Hammer test is a non-destructive concrete testing method that provides a practical and quick assessment of the compressive strength of the concrete.
How is it done?
The rebound hammer, also known as the Schmidt hammer, is made from a spring-controlled mass that slides on a plunger inside a tubular chassis. The degree of rebound, which is a test of surface hardness, is measured on a graded scale. A concrete with low strength and stiffness will absorb more energy, resulting in a lower rebound value. To take the readings, the rebound hammer is held at right angles to the surface of the concrete structure.
EN 12504-2 “Testing concrete in structures. Non-destructive testing. Determination of rebound number”
EN 13791 “Assessment of in-situ compressive strength in structures and precast concrete components”
Concrete cover and rebar detection (ferro-scanning)
Why is it used?
Ferro-scanning is used to establish concrete cover, rebar sizes and layout either to confirm information in design drawings or to support the decision when such information is missing. It can also be used when post-installed rebar is planned to avoid hitting rebar (e.g. adding anchors).
How is it used?
The Profoscope is a handheld device which uses an affordable technology based on Eddy currents to detect rebar. The device is simply activated over the area to be tested and will return results. These results can be data logged and then downloaded to a PC. More sophisticated devices based on the use of Ground Penetration Radar GPR technology or Pulse Echo technology is also available, but the Eddy current is the most commonly used.
BS 1881-204 “Recommendations on the use of electromagnetic cover-meters”
To establish the extent of carbonation in concrete. Carbonation is the most common cause of concrete reinforcement corrosion in above ground structures. It results from the reaction of carbon dioxide in the air and calcium hydroxide in the cement. Corroding rebar is six times the volume of original steel, which causes delamination of cover and spalling.
How is it used?
The carbonation test is performed on freshly exposed concrete surfaces. The surface is prepared and sprayed with phenolphthalein solution. The solution is an indicator of the concrete alkalinity and turns magenta at pH > 9.2, indicating alkalinity, and is neutral colour when pH < 9.2 indicating carbonation. The measurements are conducted soon after the colour has stabilized. The demarcation between the region, which turns into magenta and the region showing no change in colour will indicate the carbonation front.
BS EN 14630: Products and systems for the protection and repair of concrete structures and Test Methods: Determination of carbonation depth in hardened concrete by the phenolphthalein method
For more help
If you need any more help or information regarding the topics covered in this blog, please feel free to get in touch with Beta Design Consultants directly.
Beta Design Consultants was set up in 2009 and works with various industry sectors including developers, asset owners and managers, public sector clients, construction contractors, steel fabrication businesses and members of the public. With a host of experienced civil and structural engineers, Beta Design Consultants has various accreditations including Constructionline Gold, SSIP, UKAS Quality Management ISO900 and UKAS Environmental Management ISO14001.