Penetration resistance test is a concrete non-destructive test. This test determines the strength of concrete by penetrating a steel rod.
Non-destructive test (NDT) and destructive tests (DT) are the the tests done one hardened concrete. Concrete is the oldest and most important construction material in the world. Testing of the concrete plays and important role to know about the strength, durability and condition of the structure. This article is about the types of Destructive and non destructive tests done on concrete.
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Types of concrete tests
Tests on hardened concrete are classified into two types.
Non destructive tests and Destructive tests are for determining the important properties of concrete like compressive strength, flexural strength, tensile strength etc.
Non- Destructive tests
The standard method of testing hardened concrete is by testing the concrete specimens cast simultaneously with structural concrete. These tests can determine the compressive, flexural, and tensile strengths. The major disadvantage of these tests is the non availability of immediate results. Moreover, the properties of the concrete specimen may differ from what it is in the actual structure. This difference is due to pouring conditions, curing factor, compaction and concrete density, etc. These tests come under the category of destructive tests (DT). Destructive testing destroys or changes the part in some way such that even if it passes the test it is no longer fit for service.
Non Destructive test is for determining compressive strength and other properties of concrete from existing structures or buildings. NDT does not destroy or change the part such that it is still fit for service if it passes the test. The non-destructive test determines the properties of concrete or structures without their destruction. Moreover, we can study its changes over time, The measurements are repeated many times and validate in detail, and gets immediate results.
Objectives of Non destructive test
- Quality check of the existing structure.
- For determining the homogeneity, internal and external characteristics of the concrete.
- To detect the cracks and voids of the concrete structures.
- Assess the quality of concrete with the standard requirement.
- To study the ageing of concrete.
- For finding the compressive strength of structures.
- Evaluation of elastic modulus
Types of Non Destructive test
Penetration resistance test is a concrete non-destructive test. Nowadays Non-destructive test is conducted to determine the relative strength of the concrete. The non-destructive test is the method of evaluating the strength and durability of concrete without loading the specimen.
The main Non Destructive test are
- Penetration Resistance Test
- Rebound Hammer Test
- Ultrasonic Pulse Velocity Test
- Pullout Test and Pull-off Test
- Concrete Core Testing or Compressive strength test
Penetration Resistance Test
Another name of penetration resistance test is the Windsor probe test. This test determines the strength of concrete by penetrating a steel rod. The equipment used for this test is the Windsor probe test machine. Also, the penetration resistance is inversely proportionate to the concrete strength.
Relevance Codes
- ASTM C 803/ 803M- 97
- BS 1881 Part 207
Significance of Penetration resistance test
- To determine the concrete strength.
- For evaluating the uniformity of concrete.
- To identify deterioration in concrete.
- To evaluate the in-place strength.
- For investigating the presence of cracks and flaws.
Apparatus used for Penetration resistance test
The equipment to determine the strength using this test is Windsor probe equipment. It contains a gunpowder actuated driver, a loaded cartridge, a depth gauge and a hardened alloy rod. The gun powder actuated driver helps the alloy rod to penetrate the concrete surface. The probe with a blunt conical nose is made of hardened alloy. So that it should affect by corrosion. On the basis of the concrete aggregates, different probes are used. The test position should be at least 200mm apart from the edge. The maximum spacing between the probe should be 175mm. Also, the minimum spacing should be 100 mm.
Test Procedure
- Firstly, fix the equipment in an appropriate test position on the concrete surface.
- Then attach the probe to the driver.
- Drive the probe into the surface of the concrete.
- Check whether the probe is set firmly.
- Now measure the length of exposed above the concrete surface.
- Take at least three measurements and average them to evaluate the result.
Correlate the depth of penetration with the compressive strength. If the depth of penetration is low, then the strength of concrete is high and vice versa.
Limitations
- Tests only on through the thin layers of concrete surface.
- Fails to yield the absolute value of the strength.
- Damages the structures by making holes.
- The accuracy of this test is ± 25 %.
Even though the penetration resistance test has some limitations, this method is apt for the on-site estimation of concrete strength.