Creep of concrete is the continued deformation with time under applied load. Sometimes it is defined as increase in strain in concrete with time under sustained stress. This is also known as plastic flow or time yield. The rate of creep decrease with time and the creep strains at five years are taken as terminal values. Creep increases rapidly with the stress, loading at an early age of concrete, broken ballast, soft and porous aggregate, poorly graded and improperly compacted concrete. The deformation of hardened concrete is shown in Fig. below.
The Causes of Creep are.
1. Closer of internal voids of Concrete
2. Viscous flow of the cement paste inside concrete
3. Flow of water out of the cement gel inside concrete.
In reinforced concrete structures it is of advantage since it causes better distribution of stresses. For example in a R.C.C. column there is a reduction of stress in concrete and a corresponding increase of stress in steel due to creep. As another example creep relieves the high stressed portions of concrete in a continuous beam and increases the stress in the adjacent less stressed portion. Creep causes large deformations and deflections and is undesirable.
