How Are Concrete Classes Defined?

How are concrete classes defined? What are the symbols and numbers used? If you are wondering about this, please keep reading.

While the concrete classes are being defined, Turkish standards are based on the EN 206-1 standard since they comply with European norms. Concrete classes start with “C” in European standards. The meaning of C is the first letter of the concrete word.

Numbers come after the letter C. These numbers indicate the compression strength value of the concrete in MPa (Mega Pascal) or N/mm². Here you have caught your attention, there are two numbers.

The first number refers to the cylinder die strength obtained when the concrete representing the concrete is broken and the sample is accepted on the first day after the concrete is laid on the 28th day.

The second number, in the same way, refers to the cubic pressure scale of the same unit.

What is the strength of the cylinder and the cube? If you are wondering, keep reading.

Two types of molds are used when taking concrete samples. The first one is a cylinder shaped sample vessel with a diameter of 15 cm and a length of 30 cm. The other is to use a cube sample mold with dimensions of 15 cm. It is 15x15x15 cm in size.

The accepted strength results are considered to be lower than the cube mold due to the dimensional difference in the sample taken from the cylinder mold. The relation between the cylinder and the cube strength is determined according to a accepted correlation here.

 Concrete Classes Classified by Compression Strength

The definition for C25 is shown as C25/30, as shown in the illustration. Here, 25, represents the resistance of the cylinder in MPa and 30, represents the resistance of the cube in MPa. These values represent the minimum pressure strength of the concrete class. When a value falls below these values, the suitability of the concrete class is questioned.

It can also be expressed as Kgf/cm² for a better understanding of the pressure resistances. Kgf/cm² means kilogram that can be carried at 1 cm². In this point of view, it can be better understood what the compression strengths as MPa mean.

We use the coefficient 10,19 when the unit of MPa is converted to Kgf/cm². This means that for the C25/30 concrete class, 305.7 kg of load can be carried in cm² (30×10,19) at the strength of the cube. When considered in this way, the compression strengths can be understood better.