SHRINKAGE IN CONCRETE

SHRINKAGE

The shortening in length of a member or 

contraction of the concrete per unit length 

due to drying when concrete sets are 

known as shrinkage.

Shrinkage can be classified as

a) Plastic shrinkage

b) Drying shrinkage

Plastic shrinkage

This type of shrinkage manifests itself soon 

after the concrete is placed in the form 

while the concrete is still in plastic state. 

Loss of water by evaporation from the 

surface of concrete or by absorption by 

aggregate or sub grade is assumed as the 

reason for plastic-shrinkage.

As aggregate & steel restrain this effect, 

cracks appear at the surface or internally 

around aggregate or reinforcement. Thus 

shrinkage is prevented by using aluminium 

powder and expansive cement or shrinkage 

compensating cement. 

Drying shrinkage

• It is an everlasting process and occurs 

Generally due to loss of water traped in the 

gel pores when concrete is kept in 

drying condition.

• The smaller( Fine) the gel, the more is the 

shrinkage.

• Harder aggregate leads to lower 

shrinkage but higher shrinkage stress. 

Reverse is true for softer aggregate.

• Shrinkage decreases with increase in 

size of member.

• Concrete made with smaller size 

aggregate shrinkage more than 

concrete made with larger size 

aggregate.

• Shrinkage produces tensile cracks in 

any member which is restrained.

• For a given environment, the total 

shrinkage depends more on the total 

amount of water present in concrete at 

the time when mixing start and to a lesser extent on the cement content.

• In the data is not available, an apex 

value of total shrinkage strain for 

design may be taken as 0.0003 

shrinkage decreases with increase in 

relative humidity.

• ½ of total shrinkage assumed in 1st

month and 3/4th in 1st 6 months.