Strength testing of concrete

Due to its strength and longevity, concrete is one of the most commonly used building materials worldwide. But it’s essential to test the strength of concrete structures to make sure they can bear the loads and stresses they will encounter. Whether the concrete mix is being used for a large bridge or a straightforward sidewalk, this procedure aids engineers and builders in making sure the mixture is appropriate for the job.

Concrete can be tested using a variety of techniques, each of which provides a different perspective on how well the material performs. One common test is the compressive strength test, which involves applying increasing pressure to a concrete sample until it breaks. Finding out how much weight a concrete structure can support before cracking or breaking requires this test.

To determine how well concrete can tolerate pulling forces and bending stresses, tests for tensile strength and flexural strength are also performed in addition to compressive strength. These tests guarantee that construction projects are built on a strong foundation by offering a thorough understanding of concrete’s capabilities and limitations.

Anyone working in the construction industry needs to understand these testing procedures because they yield the information required to make well-informed decisions regarding design and material selection. Builders can guarantee the longevity and safety of their structures, ultimately safeguarding people and investments, by extensively testing the strength of concrete.

Why concrete is tested?

Tests are conducted on specific concrete mortar samples. Thus, the concrete’s quality is checked while a building or other structure is being built. Concrete is tested in factories and internally.

Determining the concrete grade—that is, the limits of compressive strength—is the primary goal of the tests.

Buildings whose concrete undergoes strength testing

• foundation;
• columns, pillars;
• ceilings;
• walls;
• beams;
• prefabricated structures made of concrete, reinforced concrete.

How to make samples?

Prisms, cylinders, and cubes are examples. The type of test determines their shape. Cubes are used to test compressive strength. These sizes are available for them:

• 7*7*7 cm;
• 10*10*10 cm;
• 15*15*15 cm;
• 20*20*20 cm.

The 4*4*16 cm prism is used to measure the maximum tensile strength in bending. The dimensions of cylinders are 4.4–15 cm in diameter and 8–20 cm in height. Samples must adhere to GOST 10180-90, which establishes these dimensions. When standards are broken, more processing is required to bring them up to date. The following procedures are involved in sample preparation: part of the solution selection, laying, and compaction.

Concrete cube molds are constructed from waterproof materials that prevent the passage of concrete dough. A common material for molds is steel. The mixture that will be used in the tests is taken from the middle of the mixture. Twice the volume of the samples should be exceeded by the amount of solution. It is further mixed after selection before being formed into test specimens. Fifteen minutes following mixture preparation and selection is the ideal window of time for forming. A lubricant covering the inside shape prevents the samples from developing any spots.

Mixture lay-up and compaction:

• Samples of concrete mortar with a rigidity of less than sixty, workability (P – mobility) with a mobile cone slump (OK) are made by filling the form with the mixture to the top, fastening it on a special vibrating table. Compaction occurs by vibration until cement milk appears. Instead of vibration, the bayonet method can be used to compact mobile concrete mortar with an OK greater than 12. The number of bayonets should be calculated as follows: one bayonet for every 1 cm2.
• A mortar with a rigidity greater than sixty is placed in a form with a nozzle, filled to half, covered with a load with a pressure of 4X10-4 MPa, fastened on a vibrating table. Vibration is continued until the load settles and concrete milk appears in the cracks. After removing the load, all excess is cut off, smoothed with a trowel.

Two layers are filled into forms taller than twenty centimeters, and each layer is compacted with a bayonet. Each mold’s surface is evened out using a trowel or knife, and then the measurements are recorded in the test report, weighed, and numbered.

The forms are kept in a room that is between 20 and 22°C and are covered with a damp cloth. The samples are taken out of the molds and labeled following a day of this kind of storage. The workpieces are hardened in a room with a temperature between 20 and 22 °C and nearly 100% humidity before testing.

Testing the strength of concrete is crucial to guaranteeing the longevity and security of construction projects, as it ascertains the material’s ability to tolerate a range of loads and stresses. Engineers can evaluate the quality and performance of the concrete mix and make sure it satisfies the necessary standards and specifications by conducting tests like compressive strength, tensile strength, and flexural strength. In the end, these tests contribute to the longevity and stability of infrastructure and buildings by assisting in the identification of possible weaknesses and the prevention of structural failures. Construction experts can select the best concrete mix for their particular requirements by knowing the significance of strength testing, which will result in safer and more dependable structures.

What is included in the test report?

The following columns of the protocol are used to record data regarding the outcomes of control tests:

• Serial number. Documents for concrete contain all the necessary information about the batch. You need to test one series for purity of testing, small discrepancies in results.
• Number of samples poured and test start time. The gap between these two numbers must be more than twenty-eight days.
• The type of structure includes its name, a brief description.
• Sample Options. When a test is carried out much attention is paid to their size and shape.
• Destroying load.
• Place of manufacture – laboratory. Fixed using a digital-letter designation.
• Results denoting the average strength of concrete, measured in Pascal.
• Assigning a class and brand on the basis of data obtained thanks to the tests.

Any building project requires an understanding of concrete’s strength. Engineers and builders can determine whether a material satisfies the required durability and safety standards by conducting strength tests. These tests make sure that the structures are strong enough to endure the stresses and forces they will face over time. Construction experts can avert potentially dangerous situations and costly repairs by testing concrete on a regular basis.

Concrete strength can be measured using a variety of techniques, each of which provides a different set of results. The most popular tests, like the flexural and compressive strength tests, offer important information about the performance of the material. By identifying any flaws or variations in the concrete, these tests facilitate the modification of the mix or the curing procedure. Engineers can make well-informed decisions regarding the design and construction of a building or infrastructure project by using precise testing.

Construction teams can improve the overall quality of their work and attain better results by giving priority to strength testing early in the project. Devoting time and resources to these tests increases the longevity and dependability of the structures while also guaranteeing adherence to building codes and regulations. In the end, comprehensive testing of concrete results in safer structures and a more durable built environment.

Video on the topic

Concrete tests for strength

Checking concrete for strength (chip) (in Skolkovo;)

Hydraulic press against concrete gaining strength

Checking concrete for strength in the laboratory

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Determining the compressive strength of concrete