Creep in concrete is the gradual increase in deformation (Strain) with time in a member subjected to sustained loads. The creep strain is much larger than the elastic strain on loading. If the specimen is unloaded, there is an immediate elastic recovery and a slower recovery in the strain due to creep. If the concrete is loaded again at a later date, instantaneous and creep strains develop again. Creep occurs under both compressive and tensile stresses and always increases with temperature. HSCs creep less than NSC.
The main factors affecting creep strain are the concrete mix and strength, the type of aggregate used, curing, ambient relative humidity, and the magnitude and duration of sustained loading. Refer clause 188.8.131.52 of SI 456.