Adding normal drying shrinkage to this and considering the fact that creep can be several times as large as the elastic strain on loading, it may be seen that these factors can cause considerable deflection and that they are of great importance in structural mechanics. This instantaneous recovery is followed by a gradual decrease in strain, called creep recovery. This recovery is not complete because creep is not simply a reversible phenomenon. It is now believed that the major portion of creep is due to removal of water from between the sheets of a calcium silicate crystallite and to a possible rearrangement of bonds between the surfaces of the individual crystallites. Factors Influencing Creep Concrete that exhibits high shrinkage generally also shows a high creep, but how the two phenomena are connected is still not understood.
Evidence suggests that they are closely related.
Strength of concrete has a considerable influence on creep and within a wide range creep is inversely proportional to the strength of concrete at the time of application of load. From this it follows that creep is closely related to the water-cement ratio. There is no doubt also that the modulus of elasticity of aggregate controls the amount of creep that can be realized and concretes made with different aggregates exhibit creep of varying magnitudes. The rate decreases continuously, however, and it is generally assumed that creep tends to a limiting value. It has been estimated that 75 per cent of 20-year creep occurs during the first year.