2019-02-11 | Classes of compressive strength for concrete

Our professional staff has decided to share its knowledge with you. Today, he are inviting you to read an article about classes of compressive strength for concrete. If you're curious, read on.

The most popular terms when dealing with topics related to concrete strength are their classes, for example C20/25. To find out what they mean you need to know their basic classification. Strength classes of concrete are designated with the letter "C" (lightweight concrete by letters "LC") and additionally by two numbers, e.g. C30/37, which refer to the compressive strength of concrete. Light concretes are mostly used as insulating layers. Plain concrete is used for making concrete and reinforced concrete construction elements, whereas heavy concretes are usedfor buildings requiring solid, durable construction, e.g. nuclear power plants.

Former, but still used nowadays Polish naming, took the marking of the concrete class with the letter "B" and one number defining the guaranteed compressive strength, e.g. B20 concrete.

We distinguish the strength classes of ordinary and heavy concrete light concrete  using symbols from C8/10 to C100/115 and from LC8/9 to LC80/88, respectively.

The first of the numbers indicates the characteristic strength (expressed in MPa) for compressing a sample cylinder with a diameter of 15 cm and a height of 30 cm, measured after 28 days. The second of the numbers indicates the characteristic strength (expressed in MPa) for squeezing a sample 15x15x15 cm cubic , also determined after 28 days. This second number corresponds approximately to the earlier marking of strength classes of concrete, i.e., C20/25, it is approximately B25.

The tensile strength of concrete is about ten times lower than its compressive strength. In order to transfer tensile forces reinforcement is used and this material is called reinforced concrete.

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