Creep of concrete - definition and factors affecting the concrete.

Creep is defined as gradual increase in strain without increase in stress with time. It is also known as plastic flow or time yield.  

Creep may be due to viscous flow of cement-water paste or flow of water out of the cement resulting in the closure of internal voids. It also takes place due to readjustment of molecules.

Factors affecting creep of concrete :-

1. Influence of aggregate - aggregate shows a restraining effect on creep.
• stronger the aggregate, more is the restraining effect and less is the creep.
• Light-weight aggregate shows higher creep than normal weight aggregate due to lower modulus of elasticity.

      2. Influence of mix design - 

• Creep increases with increase in w/c ratio.
• Creep is inversely proportional to the strength of concrete.
• Poor paste shows higher creep.     

      3. Age of concrete - Since quality of concrete improves with time. So older concrete is creepless whereas young concrete shows creep. After 7 days, creep co-efficient is 2.2, after 28 days, creep co-efficient is 1.6 and after 1 year, creep co-efficient is 1.1 .

Creep is desesirable in pre-stressed concrete structure whereas desireble in R.C.C. columns.

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