Guide to Concrete Grades and Their Application

The strength of the concrete used in your home's construction determines the structure's life and quality. Weak concrete could result in soft structures needing regular repairs. Concrete is a mix of materials, such as lime, sand, crushed stones, cement, and water. The proportion of the mix determines the grade of concrete. Thus, it is beneficial to understand different grades of concrete and their uses.

Define Concrete Grades

There are a variety of grades of concrete used in construction. The Bureau of Indian Standards (BIS) has established these grades based on the compressive strength of the concrete in megapascals (MPa) at 28 days. These are denoted by the prefix "M", or mix, followed by the number corresponding to the grade’s strength. The grade of concrete ratio to other components also determines its strength.

Types of Concrete Grades

Ordinary Grade of Concrete

The concrete grades M10, M15, and M20 come under the ordinary grade of concrete. These concrete grades have a low compressive strength ranging from 1,450 to 3,200 PSI and are hence used for non-structural construction.

• M10 has a compressive strength of 1,450 and is used for non-structural purposes
• M15 possesses a PSI of 2,175 suitable for constructing pavements and binding floors.
• M20’s 2,900 compressive strength makes it suitable for constructing floors, workshops, and garages.

Standard Grade of Concrete

The concrete grades from M25 to M45, which possess better compressive strength, fall in this category. They are used for constructing concrete girders, slurry pits, high-tensile beams, and loading bays. 

• M25’s 3,625 compressive strength makes it a versatile grade of concrete useful for constructing foundational structures that provide internal support.
• M30’s 4,350 PSI makes it very durable and useful for roads with a lot of wear and tear, such as harsh weather conditions and heavy vehicles.
• M35 has a compressive strength of 5,075, giving it high consistency suitable for constructing external walls of commercial buildings.
• M40 possesses a high PSI of 5,800, giving it the strength to hold heavy structures such as beams. M40 concrete grade also has anti-corrosive properties, making it suitable for constructing septic tanks that hold potent chemicals.

High-Grade Concrete

Concrete grades with PSI strength ranging from 6,525 to 9,425 are classified as high-grade concretes and include grades of concretes between M45 to M65. Due to their impressive strength and durability, high grades of concrete are used to construct high-end structures such as dams, bridges, etc. 

Uses of Different Grades of Concrete

• M10 (1,450 PSI): This grade is primarily used in non-structural areas. It's suitable for applications like patio slabs, pathways, and other projects where high strength isn't a primary concern.
• M15 (2,175 PSI): M15 concrete is ideal for sealing floors and constructing roads. It offers a good balance of strength and workability, making it versatile for various applications.
• M20 (2,900 PSI): Commonly used in residential projects, M20 concrete is suitable for flooring, garages, and sheds. It provides adequate strength for typical household needs.
• M25 (3,625 PSI): M25 concrete is a versatile choice with higher compressive strength. It can be used for foundational work and reinforcing walls, making it a popular option in construction.
• M30 (4,350 PSI): Known for its durability, M30 concrete is often used in road construction and other projects requiring resistance to heavy traffic and adverse weather conditions.
• M35 (5,075 PSI): This grade is preferred for commercial building walls and external structures due to its excellent uniformity and strength.
• M40 (5,800 PSI): When strength and durability are paramount, M40 concrete is chosen for foundations and beams. Its resistance to chemical corrosion makes it suitable for applications like septic tanks.
• M45 to M65 (6,525 to 9,425 PSI): These higher-grade concrete types find their place in substantial structures such as dams, factories, and bridges. Their exceptional strength and durability ensure the integrity of these critical constructions.

Choosing the Right Concrete Grade

Selecting the best concrete grade for your designed project  depends on several factors. Consider the expected loads and stresses the structure will endure and the local climate conditions. For reinforced concrete structures, the Indian Standard IS 456 recommends a minimum grade of M20. Beyond M20, specialised grades may be necessary for specific applications, like road construction or industrial facilities. 

Finally, understanding different concrete grades enables you to select the appropriate concrete to suit your needs. Be sure to consult experts to make the best selection.
 

Frequently Asked Questions

1. What is the grade of concrete to be used for house construction?

Ans: M20 to M25 is most suitable for domestic construction.

2. What is the PSI of concrete grades?

Ans: Pounds per square inch (PSI) denotes the strength of concrete.