All About fck of concrete (characteristic of compressive strength)


All About fck of concrete (characteristic of compressive strength)

Concrete is one of the most widely used construction materials in the world, known for its strength, durability, and versatility. Its strength is determined by its compressive strength, which refers to its ability to resist a crushing force. This characteristic is crucial in ensuring the stability and longevity of various structures, from high-rise buildings to bridges and roads. In this article, we will delve into the all-important concept of compressive strength of concrete, exploring its key features, testing methods, and factors that affect its performance. Whether you are a construction professional or simply curious about the science behind concrete, join us as we uncover all about the fck of concrete and its significance in the world of construction.

fck of concrete (characteristic of compressive strength)

fck of concrete (characteristic of compressive strength)

The fck of concrete, also known as characteristic compressive strength, is a fundamental engineering parameter that determines the load-bearing capacity of concrete. It is a measure of the maximum compressive stress that a concrete sample can withstand before it fails under a crushing force.

The term fck comes from the French phrase “fond de compression,” which translates to “compressive strength.” It is denoted as fck, where “f” stands for the characteristic strength of concrete and “ck” stands for “concrete characteristic.”

The fck of concrete is an essential characteristic that engineers consider in the design and construction of various structures such as buildings, bridges, roads, and other infrastructures. It is a crucial factor that determines the quality, durability, and safety of a concrete structure.

Several factors influence the fck of concrete, including the materials used, water-cement ratio, mixing process, curing conditions, and age of the concrete. The type and size of aggregates used in concrete also play a significant role in determining its compressive strength.

The fck of concrete is usually expressed in units of pressure, such as megapascals (MPa) or pounds per square inch (psi). The standard way of determining the fck of concrete is by performing a series of compression tests on cylindrical or cubic specimens at a given age.

Based on the results of these tests, the average fck value is calculated, which is used to design and analyze the load-bearing capacity of concrete structures. The characteristic compressive strength is generally defined as the lowest fck value of all the samples tested.

Engineers must take into account the fck of concrete when selecting the appropriate concrete mix design for a specific structure. For example, a high-rise building requires a higher fck value compared to a residential driveway.

The fck of concrete varies for different types and grades of concrete, ranging from 10 MPa to as high as 100 MPa. The type of structure and the expected load conditions determine the required fck value.

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In conclusion, the fck of concrete is a crucial parameter in concrete design and construction. It is a measure of the strength and durability of concrete, which directly affects the safety and longevity of structures. As a civil engineer, understanding and accurately determining the fck of concrete is essential for ensuring the safe and successful completion of projects.

What is fck of concrete & their full form

What is fck of concrete & their full form

Fck of concrete refers to the characteristic compressive strength of concrete, measured in megapascals (MPa). It is a key parameter that is used to determine the quality and strength of concrete in structural design.

The term “fck” is an abbreviation for “characteristic compressive strength” in German, which translates to “Karakteristische Druckfestigkeit.” The standard notation for “characteristic compressive strength” is fck, with a subscript c to indicate that it is a compressive strength value. In English, “fck” is also commonly referred to as “f’c” or “f’ck.”

The characteristic compressive strength of concrete is the strength at which 95% of all concrete test samples are expected to fail. This means that only 5% of all test samples will have a compressive strength higher than fck. It is important to note that fck is not the actual strength of a concrete sample, but rather an estimated value used in design calculations.

There are two main methods to determine the fck of concrete: destructive and non-destructive testing. Destructive testing involves breaking a concrete sample and measuring its compressive strength in a laboratory. Non-destructive testing uses methods such as ultrasonic pulse velocity, rebound hammer or maturity testing to estimate the strength of concrete without destroying the sample.

The fck of concrete is influenced by many factors such as the quality of materials used, water-cement ratio, curing process and age of concrete. As a rule of thumb, the compressive strength of concrete increases with its age. Fresh concrete usually has a lower fck value compared to cured concrete of the same batch.

Understanding the fck of concrete is crucial in structural design and construction. It is used to determine the amount and type of reinforcing steel that should be used in a concrete structure, as well as the required concrete strength to withstand applied loads. It also helps in determining the appropriate mix design for concrete, balancing strength and economy.

In conclusion, fck of concrete refers to the characteristic compressive strength of concrete, measured in MPa, which is used in structural design and construction. It is an important parameter that influences the quality, strength, and durability of concrete structures.

fck of concrete compressive strength testing machine (CTM)

fck of concrete compressive strength testing machine (CTM)

Fck of concrete compressive strength testing machine (CTM) is an essential tool used by civil engineers to determine the strength of concrete. This strength is measured by subjecting concrete cubes or cylinders to compressive forces until they fail or break. The capacity of the CTM ranges from 100 kN to 5000 kN and can be used for testing a wide range of concrete mixes.

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The acronym fck stands for “characteristic compressive cube strength”, which is the maximum compressive strength that a concrete cube of a specific grade can withstand. The fck value is determined by conducting multiple compressive strength tests on concrete specimens and taking the average value of the results.

The CTM consists of a sturdy frame with two steel plates, a top plate and a bottom plate, each with a flat circular surface for placing the concrete specimen. The top plate is attached to the CTM’s hydraulic cylinder, while the bottom plate is fixed to the base of the machine.

To begin the testing process, the concrete cube is placed in between the two plates and the load is applied to the top plate gradually and continuously until the cube fails. The force required to cause failure is recorded by the machine’s load cell, and the fck value of the concrete is determined.

The CTM also has a digital display unit that shows the load applied and the corresponding deformation or displacement of the specimen. This allows engineers to monitor the behavior of the concrete under the applied load and determine its strength.

The fck value of concrete is important in construction as it helps engineers determine the appropriate grade of concrete to be used in a specific structure. Different types of structures require different grades of concrete with varying fck values, and the CTM plays a crucial role in ensuring that the concrete used meets the required strength.

Regular calibration and maintenance of the CTM is essential to ensure accurate and reliable results. The machine should also be operated by trained professionals to avoid any errors or accidents.

In conclusion, fck of concrete compressive strength testing machine (CTM) is a crucial factor in determining the strength of concrete and ensuring the safety and durability of structures. With the use of this machine, civil engineers can accurately assess the quality of concrete and make informed decisions in construction projects.

fck of concrete Test ,Rules and result

fck of concrete Test ,Rules and result

The fck of concrete test is an important procedure used to determine the compressive strength of concrete. It is an essential test to assess the quality and durability of hardened concrete in a construction project. The term “fck” stands for “characteristic compressive strength”, which is defined as the strength of concrete that has a 95% chance of exceeding the specified compressive strength value.

The fck of concrete test is carried out in accordance with the guidelines set by various international standards such as ASTM, BS, EN, and ACI. The test involves casting and curing of concrete samples in the laboratory under controlled conditions. The samples are then subjected to compressive loading to failure, and the maximum load at failure is recorded.

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Rules for Conducting the fck of Concrete Test:

1. Selection of Samples: Samples for fck test are usually taken from the concrete batch at the time of casting. The size and number of samples required depend on the size and type of the construction project. Usually, at least three samples are taken for testing.

2. Curing: The samples are cured in a water tank or under wet burlap for a specified period of time before testing. This ensures the samples have a similar moisture content and age as the in-situ concrete.

3. Loading: The tested samples are placed in a compression testing machine, and a compressive load is applied gradually until failure. The loading rate is typically 0.2 MPa per second.

4. Recording Data: The compressive load at failure is recorded, and the average value is calculated for each set of samples. The compressive strength of concrete at 28 days is calculated by dividing the maximum load at failure by the cross-sectional area of the sample.

Results and Interpretation:

There are different classes of concrete, each with a specified compressive strength. The fck of concrete test is used to ensure that the concrete in a construction project meets the required standards. The result of the test is compared with the specified compressive strength of the concrete to determine if it is acceptable for use in the project.

In case the tested concrete fails to meet the specified compressive strength, further testing is carried out to determine the cause of the failure. Some possible reasons for low compressive strength of concrete include incorrect mix proportions, inadequate curing, or poor workmanship.

In conclusion, the fck of concrete test is an important quality control measure for ensuring the strength and durability of concrete in construction projects. It helps to identify any potential issues with the concrete mix or construction process, allowing for timely corrective measures. As a civil engineer, it is essential to follow the standard testing procedures and rules to ensure accurate and reliable results.


In conclusion, understanding the characteristic of compressive strength of concrete is crucial in ensuring the safe and reliable use of this widely used building material. By knowing its fck value, concrete can be designed and tested for its maximum load-bearing capacity, making it suitable for various construction applications. It is important to note that factors such as material quality, mixing techniques, and curing conditions can greatly affect the fck value, hence proper handling and quality control measures should be implemented. As technology advances, the knowledge about concrete fck will continue to improve, leading to the development of stronger and more durable structures. By constantly learning and staying updated on the characteristics of concrete, we can ensure the longevity and strength of our built environment.


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