Grade of Concrete: Meaning, types and uses

To be considered grade, concrete must meet certain minimum standards for strength after 28 days of curing under controlled conditions. When referring to the quality of concrete, the letter M is appended to the specified strength in MPa. Concrete is categorised into many mixed kinds depending on its compressive strength.

Cement, sand, aggregate, and water are combined in a predetermined ratio to create concrete, which is then used to form a 150 mm cube that is cured in a water bath for 28 days before being subjected to compression testing. The grade of concrete is the outcome of compressive stress testing. The SI unit is Newton per millimetre squared. According to their compressive strength, concrete grades are designated as M10, M20, M30, etc.

See also: Micro concrete: Applications, advantages and challenges

Grade of concrete: Types

There are three different types of grades of concrete. These include:

Normal mix grade concrete

Nominal mix grades include M5, M7.5, M10, M15, and M20 for concrete. They have low compressive strength (between 1,450 and 3,250 PSI). Pavements, garage floors, and outdoor parking lots are common uses for them, all of which are non-structural.

Standard concrete grade

Common types of concrete include M25, M30, M35, M40, and M45. Typically, footings, columns, slabs, beams, and other RCC elements are built with concrete grades ranging from M25 to M35. While commercial structures, runways, concrete highways, pressurised concrete girders, RCC columns, pressurised beams, etc., are constructed with higher classes like M40 and M45.

High-strength concrete type

Cement of grades M50, M55, M60, M65, and M70 is considered high-strength concrete. It ranges from 6,525 to 9,425 PSI in compressive strength. High-rise buildings and structures near bodies of water are common uses of this kind of concrete.

Grade of concrete: Uses

How to select the best grade of concrete?

To provide the necessary structural strength and form, concrete is used. This implies that it depends on the loads that will be exerted on the building. For RCC, IS 456 specifies a minimum grade of M20 for concrete. For concrete up to the M20 strength level, standard cement is used.

Different types of cement exist to meet a variety of requirements. Examples include concrete factories, prefabricated buildings, and nuclear power reactors built on beaches. Concrete with enhanced chemical and corrosion resistance will be utilised there. M30 is the standard for road concrete. Similarly, concrete grades between M35 and M45 are employed for very long-lasting commercial projects.

What are different concrete grades?

The composition and strength of concrete are determined to give the mix a grade. There are several concrete grades:

• Ordinary concrete grade: This includes three types – M10, M15 and M20. These have relatively low strength ranging between 1,450 to 3,250 pounds per square inch (PSI). They are used for constructing pavements, garage floors, parking areas, etc.
• Standard concrete grade: This category includes concrete grade ranging between M25 to M45. It is used to build high-tensile beams, walls, concrete girders, loading bays, and slurry pits, etc.
• High concrete grade: This includes concrete with over 50 MPa with compressive strength ranging between 6,525 and 9,425 PSI. The application of this type is mostly in the construction of high-rise buildings and structures around water bodies.

Which is the best type of concrete grade?

The choice of the type of concrete grade will depend on the application. For example, M20 and M25 concrete grades are ideal for domestic construction while M30 is suited for road construction. In case of heavy commercial constructions, concrete grades ranging between M35 and M45 are preferable due to their high durability.

Further, one should consider the compressive strength of the concrete grade. For instance, cement with a compressive strength ranging between 4,350PSI and 5800PSI are chosen for heavy construction supporting heavy structure.

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