When a builder claims that his buildings are the strongest and most durable he invariably means that the building’s concrete, apart from all other material used, is of the best quality and there are methods to verify these claims, writes Nemmani Sreedhar

Our rendezvous with concrete is indeed very old. From being associated with building materials to becoming an adjective, the word concrete has become synonymous with modern construction as well as the very notion of strength. While there is a long lineage of technologies used in building the structures that are fit for human habitation, can anyone imagine a construction without using concrete these days?

No wonder, when a builder claims that his buildings are the strongest and most durable he invariably means that the building’s concrete, apart from all other material used, is of the best quality. But how do we verify these claims? The only thing that a layman can do is visual inspection through which one can determine that a structure is devoid of any irregularities or visible fractures.

So how can we be sure that the builder’s claims are correct and that concrete column, beam or slab is internally strong? Fortunately the modern technology comes to our rescue to check not just the strength of a column; there are also ways to determine the consistency of a concrete block.

One of the methods for testing a column is the ‘Core Test’. In this test, a core of 4 inch diameter is taken out through specially designed drilling equipment. This core is then examined and subjected to various tests. “The premise behind this testing is that as the core is drilled out of the main structure, it can represent the entire structure. To be effective, the cores have to be drilled at regular intervals,” construction material expert, L.H. Rao says.

Though this type of testing gives a direct measure of a building’s strengths there are few drawbacks with it. Since a core has to be drilled out of a structure, appropriate care should be taken so as not to cut the steel bars used to reinforce the concrete. To avoid this possibility, one should first determine the location of the steel bars through specialised tests like Resistivity method or Half-Cell Electrical Potential methods. Because of these complications, core test should be conducted only by professionals who are thoroughly versed with the procedure or there is a danger of undermining the strength of the structure, Dr. Rao cautions.

“Due to the nature of tests adopted in this process, core tests are mainly suitable for determining the strength of major projects like dams and bridges or on big constructions. Being a semi-destructive testing method, this test may not be the best option for smaller buildings and constructions,” he says.

But the latest technological developments have left us with few more methods, in the form of non-destructive testing, which can be very helpful in determining the strength of a building without harming the structure in any fashion. Chief among then is ‘Ultrasonic Pulse Velocity Testing’.

Ultrasonic waves are high frequency sound waves, and like in medicine, they can be used to draw the internal images of structures and detect any anomaly. “In the Ultrasonic testing method, ultrasound waves are passed into a concrete slab through a transducer and its echo is caught through another transducer. Through this process the internal health and structure of a concrete can be easily deduced,” Dr. Rao says.

Qualities like density of the concrete, health of the materials used and the strength of a slab can be easily measured by this type of testing. “Since there is no physical damage to a concrete structure and since the test can access the internals of any structure, this type of testing is ideal for even smaller constructions,” Dr. Rao adds.

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