Properties of Concrete

What are the properties of concrete ? 

Concrete is the most used building material in construction industry. It is a mixture of cement and aggregate. There are many properties of concrete and followings are some of them.

1.Grade of Concrete
2.Compressive Strength in Concrete
3.Characteristic Strength in Concrete
4.Tensile Strength in Concrete
5.Shrinkage in Concrete
6.Creep in Concrete
7.Modular Ratio
8.Poisson's Ratio
9.Durability of Concrete
10.Unit Weight of Concrete

1.Grade of Concrete

Concrete is introduced by its grades designated as M15 , M20 ,M25 etc. The meaning of M is the mix and number of 15, 20 or 25 denoted the specified compressive strength (fck) in 150mm cube at 28 days. The unit is N/mm2.

2.Compressive Strength in Concrete

The compressive strength of concrete is the capacity of concrete to withstand loads tending to reduce the size. Compressive strength of concrete also is a quality which varies considerably for the same concrete mix. 

3.Characteristic Strength in Concrete

The characteristic strength of concrete is defined as strength below that not more than 5% of the test result are expected to fail.

4.Tensile Strength in Concrete

The tensile strength of concrete in the direct tension is gained in experimentally by split cylinder. It varies between  1/8 to 1/12 of the compressive strength of a cube.

The estimate of flexural tensile strength / modulus of rapture / cracking strength of concrete from cube compressive strength is obtained by the relations fcr = 0.7 fck N/mm2.

5.Shrinkage in Concrete

The shrinkage of concrete is the property of diminishing the volume during the process of drying and hardening. Mainly it is depend on duration of exposure. If this strain is prevented, it produced tensile stress .in the concrete and hence concrete may develop cracks.

6.Creep in Concrete

Creep of concrete is defined as the plastic deformation under a sustained load. Creep strain primarily depends on duration of sustained loading. According to the standards, value of the ultimate creep coefficient is taken as 1.6 at loading after 28 days. 

7.Modular Ratio

Modular ratio is defined as the ratio between modulus of elasticity of steel to the modulus of elasticity of concrete.

Modular Ratio = Es / Ec (Es = Modulus of elasticity of steel , Ec = Modulus of elasticity of concrete)

8.Poisson's Ratio

Poisson's ration is defined as the ration between changing of lateral width per unit width to axial length per unit length due to the axial load. The poisson's ratio varies between 0.1 for high strength 0.2 for some week mixtures. It;s generally taken as 0.15 for strength design and 0.2 for serviceability criteria.

9.Durability of Concrete

The ability to resist disintegration and decay is defined as durability of concrete. One of the main characteristics influencing durability of concrete is its' permeability to increase water and other potentially deleteries materials. 

10.Unit Weight of Concrete

Unit weight of concrete mainly depends on,

1.Percentage of reinforcement

2.Types of aggregate

3.Amount of voids

Unit weight of concrete varies from 23 KN/m2 to 26 KN/m2.The unit weight of plain reinforced concrete as specified by IS 456 are 24 KN/m3 and 25 KN/m3 respectively.