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.
In concrete mixes, the hardened cement paste primarily contributes to creep, while the aggregates in the mix restrain creep.
Aggregates with a high modulus of elasticity, being stiffer, reduce creep. Hence, the greater their volume in the concrete, the lower the creep.
Creep linearly increases with the stress applied within design limits. Beyond the design limits, creep increases non-linearly with the applied stress.
Consequently, for concrete mixes with similar cement paste content, lower water-to-cement ratio mixes exhibit higher strength and less creep.
Moreover, as the age of load application increases, the creep decreases as the concrete gains strength with time.
Curing concrete at elevated temperatures before loading enhances its strength, further reducing creep.
Early-loaded members with high-early-strength cement have less creep than those with ordinary Portland cement.
Admixtures in concrete that increase the volume of fine pores holding moisture lead to increased creep.
Lastly, the concrete member's size and the relative humidity of the surrounding air affect creep. The higher the relative humidity, the lower the creep, and larger members exhibit less creep at constant relative humidity.
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