8.10
Curing of Concrete
The hydration of cement takes place within the water-filled capillary pores. However, environmental elements can disrupt this process by evaporating w…
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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Q1: Why is curing necessary for concrete after it is placed?
Curing prevents water loss from concrete by maintaining adequate moisture and temperature needed for cement hydration to continue. Environmental factors like air temperature, humidity, and wind cause evaporation from the concrete surface. Without curing, concrete achieves only about 50 percent of the compressive strength of continuously moist-cured concrete and becomes prone to shrinkage and surface cracking.
Q2: What happens to concrete if it dries without proper curing?
Uncured concrete left to dry in air experiences shrinkage, leading to surface crack formation. It also develops significantly reduced compressive strength, reaching only approximately 50 percent of the strength achieved through continuous moist curing. Additionally, the concrete becomes less durable and more susceptible to water penetration and environmental damage.
Q3: How does curing duration affect concrete strength development?
The higher the duration of curing, the higher the compressive and tensile strength of concrete. Concrete continuously cured over 28 days develops significantly greater strength compared to shorter curing periods. This direct correlation between curing time and strength development underscores why extended curing is critical for achieving optimal structural performance and durability.
Q4: What is self-desiccation in sealed concrete?
Self-desiccation occurs in sealed concrete with a water-cement ratio below 0.5, resulting in internal water loss. When concrete is sealed, free water cannot evaporate from the surface, but internal drying still occurs as hydration products fill the capillary pores. This process reduces available moisture needed for continued cement hydration and can compromise concrete quality.
Q5: Where does cement hydration take place in concrete?
Cement hydration occurs within the water-filled capillary pores of cement paste. During curing, hydration products gradually fill these pores, eventually segmenting the capillaries and making the concrete impermeable and durable. This process requires continuous moisture and appropriate temperature conditions to proceed effectively.
Q6: How do different concrete types respond to curing conditions?
Air-entrained concrete is less influenced by curing conditions than non-air-entrained concrete. Curing effects are more prominent in thinner structural elements and mixes with high cement content. Lightweight aggregate concrete is less affected by curing variations, meaning different concrete compositions require tailored curing strategies to optimize strength and durability.
Q7: What properties beyond strength does curing improve in concrete?
Curing ensures desirable properties including durability, water tightness, resistance to abrasion, and freeze-thaw resistance. By maintaining moisture and temperature during hydration, curing allows hydration products to fill capillary pores completely, creating an impermeable structure. These enhanced properties make cured concrete more resistant to environmental degradation and chemical attack.