Grades of Concrete| Types, Ratios and Applications

Concrete is one of the most commonly used construction materials today. It finds a wide range of applications, from patios to high-rise structures with reinforcement. The basic constituents of concrete are cement, fine aggregate, coarse aggregate, and water. Based on the purpose and location of use, the ratio of these materials will vary.

The grade of concrete is a common way of classifying concrete based on its strength on hardening. It is denoted using M n, where M stands for mix. The number n it is followed by denotes its characteristic strength after 28 days of curing. 

The different grades of concrete as per IS 456 are

1. Ordinary concrete
   • M 5
   • M 10
   • M 15
   • M 20
2. Standard concrete
   • M 25
   • M 30
   • M 35
   • M 40
   • M 45
   • M 50
   • M 55
3. High strength concrete
   • M 60
   • M 65
   • M 70
   • M 75
   • M 80

1. Ordinary-grade of concrete

These include concrete from grade M 5 to M 20 and not used in load-bearing members.

• Mix ratio (cement:sand: aggregate)
  • M 5- 1:5:10
  • M 10- 1:3:6
  • M 15- 1:2:4
  • M 20- 1:1.5:3
• Properties
  • They have comparatively low compressive strength and are fit to be used in non-structural components mostly as PCC (Plain cement concrete)
• Uses
  • M 5- in foundations, separate the soil and foundation concrete.
  • M 10- in construction of roads, leveling courses, bedding for concrete
  • M 15- in the construction of roads and in footing bedding
  • M 20- used as RCC (Reinforced Cement Concrete) in the construction of slabs, beams, columns, and footings of mild exposure

Villa Geldrop by Hofman Dujardin Architects

The basement-level patio of a villa in Amsterdam is made of ordinary-grade concrete.

2. Standard grade of concrete

It consists of concrete from grades M 25 to M 55 and is used in RCC and load-bearing structures.

• Mix ratio(cement:sand:aggregate)
  • M25 is made using a nominal mix ratio of 1:1:2
  • All other grades from M 30 to M 55 are made using design mix ratios, as dictated by the IS 10262
• Properties
  • The concrete mixes in this grade have comparatively higher strength and are used in RCC work and in pre-stressed concrete work.
• Uses
  • M 25- used in constructing foundations, walls, slabs, beams, columns
  • M 30- in heavy use roads, RCC structural members
  • M 35- in external wall and slab construction, structural oiling
  • M 40- in members where corrosion is expected and in prestressed concrete members
  • M 45- for runways, prestressed girders and beams
  • M 50- used in prestressed girders and piers
  • M 55- used in prestressed members and pressurized concrete girders and beams

Fine Arts Museum by Estudio de Arquitectura Hago

Prestressed concrete panels made of ordinary grade concrete are used to add details and intricacy to the facade of this museum in Badajos.

3. High-strength concrete

It consists of concrete grades from M 60 to M 80. HRWRA (High range water reducing admixtures) or superplasticizers are often added to get the desired workability. 

• Mix ratio- All high-strength cement grades use design mix ratio as per IS 10262
• Properties
  •  High compressive strength
  • Smooth fracture plan
  • Less permeability
• Uses
  • In RCC frameworks where high strength is required
  • In high-rise buildings
  • For long spans of bridges

Barnacre Equilibrium Tank by Ian Simpson Architecture

These are proposed houses to be made by repurposing old water reservoir tanks, which are made of high-strength concrete.

Depending on the usage of the concrete and the required properties, the grade of concrete can be decided upon.