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Characteristic Strength Of concrete

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Characteristic Strength Of concrete

The classification of concrete grades is based on their compressive strength. Each concrete grade e.g. C30/37 is characterized by two equivalent strengths, which in this specific example are 30 MPa and 37 MPa. The first is the characteristic strength fck of a standard concrete cylinder and the latter is the characteristic strength of a standard concrete cube.

The concrete grades mentioned in Eurocode 2 and EN 206-1

C12/15 C16/20 C20/25 C25/30 C30/37 C35/45 C40/50 C45/55 C50/60
Secondary Uses Usual Uses
C55/67 C60/75 C70/85 C80/95 C90/105
Special Uses

Minimum concrete cover of reinforcement steel and minimum suggested concrete grade

  Environmental Conditions Category
Usual Conditions

(XC2/XC3)

 Extreme Conditions

(XC4)

 Sea-side conditions

(XD1/XS1)

 Pools

(XD2)
Suggested Concrete Grade C30/37 C30/37 C30/37 C30/37
Minimum Cover 25 mm 30 mm 35 mm 40 mm
Suggested Favorable Concrete Grade C35/45 C40/50 C40/50 C40/50
Minimum Cover 20 mm 25 mm 30 mm 35 mm

The protection of reinforcement steel against corrosion depends on the porosity, the quality and the thickness of the concrete cover. The density and quality of the concrete cover are assumed using the stipulated concrete grade.

Examples

Example 1: Construction in the sea-side area with a concrete grade of C30/37

Example 2: Construction in the sea-side area with a concrete grade of C40/50 produced with quality assured production procedure

Exceeding a defined limit, the more water the concrete mixture contains, the less its strength and the higher its porosity. Apart from its strength, concrete is also characterized by its workability. Workability defines the amount of water to be used for the production of the mixture. The slump height is the workability criterion of concrete. Depending on the use of the concrete mixture a specific value of slump height is recommended.

Workability concrete classes

Exceeding a defined limit, the more water the concrete mixture contains, the less its strength and the higher its porosity. Apart from its strength, concrete is also characterized by its workability. Workability defines the amount of water to be used for the production of the mixture. The slump height is the workability criterion of concrete. Depending on the use of the concrete mixture a specific value of slump height is recommended.

Ordering concrete

When ordering a pre-mixed concrete the supplier must be given at least the following data:
(a) Quantity: e.g. 60 m
(b) Concrete Grade e.g. C30/37
(c) Slump Class: e.g. S3
(d) Super-plasticizer: e.g. YES (placed on order at the building site)
(e) Pump’s size: e.g. 36 m
(f) The time between truckloads: e.g. every 30 minutes
(g) Environmental exposure category e.g. S1 (seaside environment).
(h) Concrete strength category e.g. ΙΙ / 42.5.
(i) The maximum nominal value of the largest aggregate grain e.g. π.χ. 31.5 mm.
(j) The maximum ratio of Water/ Concrete (Ν/Τ), e.g. Ν/Τ ≤ 0.55.
(k) Compliance to ΕΝ 206-1 form.

Concrete amount less than 20 m³
For an amount of concrete lesser than 20m³, 3 test samples must be taken from different mixing drums. This means either 3 samples from the same mixing drum or 3 samples from each drum, in cases that 2 mixing drums are needed for the concreting process.

 

Concrete amount from 20 m³ to 150 m³

For an amount of concrete ranging from 20m³ to 150m³, 6 test samples must be taken from 6 different drum mixers.
A concrete amount greater than 150 m³

For an amount of concrete greater than 150m³, 12 samples must be taken from 12 different drum mixers. Samples must be taken from different concrete mixers and must be transferred to a certified laboratory for special curing within 20 to 32 hours.

Click Here To See Concrete Slump Test Definition, Procedure And Types Of Slump Test

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