10.4 : Factors Affecting Creep

In normal-weight aggregate concrete, the hardened cement paste is the primary contributor to creep, whereas the aggregates, being stiffer than the cement paste, are more resilient to stress-induced deformation. The stiffness of the aggregates is defined by their modulus of elasticity, and the more voluminous they are in the concrete, the less it will creep.

Further, the water/cement ratio is critical, as a lower ratio increases concrete strength, thus reducing creep. The strength of the concrete at the time of loading is inversely related to the creep; stronger concrete exhibits less creep. As concrete strength increases with time, applying loads at later stages diminishes creep. Commonly, creep is directly proportional to the applied stress within the range of working stresses. When stress levels exceed the material's strength, microcracking in concrete accelerates creep.

Environmental factors such as relative humidity and temperature during curing also influence creep. Higher humidity levels and higher curing temperatures result in decreased creep. Cement types that gain strength faster, and admixtures that tend to refine pore volumes to hold more moisture, both contribute to increased creep. The size of the concrete member, expressed in volume-to-surface ratio, also contributes to creep; the higher the ratio, the less creep.