The hydration of cement takes place within the water-filled capillary pores. However, environmental elements can disrupt this process by evaporating water from the concrete surfaces. Sealed concrete with a water-cement ratio below 0.5 experiences self-desiccation, leading to water loss. The water loss in concrete is mitigated by curing. This technique involves keeping the concrete saturated to maintain the necessary temperature and moisture conditions, to optimally fill the spaces in the cement paste initially occupied by water with hydration products. Curing starts after the cement has attained the final set. Concrete left to dry without curing may shrink and crack and will likely only reach half the strength of concrete that is continuously cured over 28 days. The duration of curing correlates directly with the concrete's final compressive and tensile strength, underlining the importance of this practice not only for strength but also for ensuring other desirable properties like durability, water tightness, resistance to abrasion, and freeze-thaw. This effect is more prominent in thinner structural elements and mixes with a high cement content, whereas lightweight aggregate concrete is less affected. Moreover, air-entrained concrete is less influenced by curing conditions than non-air-entrained concrete.
Cement hydration occurs in the water-filled capillary pores of cement paste.
Environmental factors like air temperature, humidity, and wind can cause evaporation, removing water from the surface of newly placed concrete.
Alternatively, if the concrete is sealed and its water-cement ratio is less than 0.5, the internal drying results in a loss of free water.
Curing prevents water loss from concrete by saturating the concrete to maintain adequate levels of moisture and temperature required to continue the hydration process.
After the cement attains its final set, curing is commenced and continues until the capillaries in the hydrated cement paste get segmented due to filling up with hydration products, making the concrete impermeable and durable.
If concrete is left to dry in the air without curing, it is prone to shrinkage, leading to the formation of surface cracks. Moreover, it achieves only about 50 percent of the compressive strength of concrete that has been moist-cured continuously.
Lastly, the higher the duration of curing, the higher the compressive strength of the concrete.
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