A Guide to Non-destructive Testing of Concrete

Testing the properties of hardened concrete is often an important step in determining the suitability of a structure for its intended purpose. Non-destructive testing methods help us evaluate concrete via an assessment of its key attributes such as cracking, permeability, corrosion of reinforcement, and void structure. Non-destructive testing of concrete is important for evaluating new as well as old structures. In case of new structures, this is done primarily to assess the quality of materials. On the other hand, testing for existing structures is performed to determine structural integrity. 

Objectives of Non-Destructive Testing

  • Estimation of compressive strength at the site.
  • Estimation of homogeneity and uniformity.
  • Quality determination with reference to the standard requirement.
  • Detection of voids, cracks, and other imperfections.
  • Identifying areas with less integrity compared to others.
  • Monitoring concrete structure changes occurring over a period of time. 
  • Reinforcement profile identification and measurement of the bar diameter, cover, etc.  
  • Determination of chloride, sulphate, and alkali content.
  • Assessment of grouting condition in prestressing ducts.
  • Elastic modulus measurement 

Most Popular Non-Destructive Testing Methods

Penetration Test: The best way of testing penetration is the Windsor probe.  In this method, the compressive strength of concrete can be determined quickly and accurately.  This involves penetrating a concrete surface by using a powder-actuated charge driven hardened steel probe. This method can be an extremely useful option while estimating concrete’s compressive strength to assess its relative strength and quality in different parts of a structure. The Windsor probe is small enough to be used in fields and can be operated easily without any extensive training.  

Concrete Test Hammer: This testing method is used for determining in-place uniformity and strength of concrete. It can be particularly useful because of its ability to delineate deteriorated concrete or regions of poor quality. The testing method involves releasing a spring-loaded hammer to impact against a piston placed in contact with the concrete surface. The distance by which the hammer bounces back is measured on a linear scale by a sliding indicator. Then, the relative and proportional strengths for different areas of a structure are determined by cross-referencing the rebound number to an actual compressive strength value. This method is best suited for establishing a structure’s relative strength profile.

Pull-Out Test: Making use of a special ram, this testing methodology measures the required force for pulling a special type of steel rod in the concrete. The enlarged end of this rod is thrown to a depth of three inches in the concrete.  Though the concrete is simultaneously under tension and shear, the force required for pulling it depends on the compressive strength of concrete. Therefore, this test provides a quantitative measure of concrete’s in situ strength after making appropriate correlations.  

Ultrasonic Pulse Velocity Test: In this test, piezoelectric transducer emitting vibrations are placed in contact with concrete surfaces. This allows vibrations to travel through the concrete, and to be received by another transducer in contact with the test objects’ opposite face.  Some popular applications of this method include measurement of surface crack depth, estimation of concrete strength, determining dynamic modulus of elasticity, establishing concrete’s homogeneity, and more.  

These were just a few non-destructive methods for concrete testing. At Coating Management solutions, concrete assessment is one of our many areas of specialisation. Contact our experts if you have any questions about concrete testing.