Creep of concrete

Creep

• When concrete is subjected to sustained
loading, its deformation keeps on
increasing with time, even though the
stress level is not altered.
• Time dependent component of total
strain is called creep.

Creep of concrete

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• Creep  occur due to:

1) Internal movement of adsorbed
water
2) Viscous flow or sliding between gel
particles
3) Moisture loss
4) Growth in micro cracks

• Effect of creep are 

1) Increase in deflection of beams and
slabs
2) Increased deflection of slender
column that may lead to buckling
3) Gradual transfer of load from
concrete to reinforcing steel in
comp. members
4) Loss of prestress in prestressed
concrete

• Beneficial effects of creep are:

1) Reduction in stress induced by non-
uniform load or restrained
shrinkage
2) In indeterminate structure, stress
induced due to settlement of
support is reduced due to creep.

• Factors influencing creep

Creep increase when:-
(a) Cement content is high
(b) W/c ratio is high
(c) Aggregate content is low
(d) Air entrainment is high
(e) Relative humidity is low
(f) Temperature (causing moisture loss)
is high
(g) Size/thickness of member is small
(h) Loading occurs at early age
(i) Loading sustained over a long period
Creep coefficient for design

Effect of creep can be reduced by

1) Using high strength concrete
2) Delaying the application of finishes,
partitions walls etc.
3) Adding reinforcement
4) Steam curing under pressure.