Short Answer

Hardened concrete is the stage of concrete after it has set and gained strength. In this stage, concrete becomes solid, strong, and capable of carrying loads.

This stage occurs after hydration of cement is complete to a certain level. Hardened concrete shows properties like strength, durability, and resistance to environmental effects, which are important for long-lasting structures.

Detailed Explanation:

Hardened Concrete

Hardened concrete is the final stage of concrete after it has completed its setting process and gained sufficient strength. When concrete is freshly mixed, it is in a plastic state, but after some time, due to the hydration of cement, it starts setting and eventually becomes hard. This hardened state is what gives concrete its structural value.

In this stage, concrete becomes strong enough to bear loads and resist different types of forces such as compression, tension (to some extent), and shear. The quality of hardened concrete depends greatly on how well the fresh concrete was mixed, placed, compacted, and cured. If these processes are done properly, the hardened concrete will be strong and durable.

1. Strength of Hardened Concrete
   Strength is the most important property of hardened concrete. It mainly depends on the water-cement ratio, curing conditions, and quality of materials used. Compressive strength is the most commonly measured strength because concrete is very strong in compression. Proper curing increases strength over time.
2. Durability of Hardened Concrete
   Durability refers to the ability of concrete to resist environmental effects such as weathering, chemical attack, and moisture. Hardened concrete with good durability can last for many years without damage. Proper mix design and curing improve durability.
3. Permeability of Hardened Concrete
   Permeability is the ability of concrete to allow water or liquids to pass through it. Low permeability is desirable because it prevents water and harmful chemicals from entering the concrete. Proper compaction and curing reduce permeability.
4. Shrinkage of Hardened Concrete
   Shrinkage is the reduction in volume of concrete as it dries. It occurs due to loss of moisture. Excessive shrinkage can lead to cracks, which weaken the structure. Proper curing and mix design help in reducing shrinkage.
5. Creep of Hardened Concrete
   Creep is the slow deformation of concrete under constant load over time. It is a long-term effect and depends on stress level, age of concrete, and environmental conditions. Proper design and material selection help in controlling creep.
6. Density of Hardened Concrete
   Density refers to the compactness of concrete. Higher density means fewer voids and stronger concrete. Proper compaction and mix proportion increase density and improve strength and durability.
7. Factors Affecting Hardened Concrete
   The properties of hardened concrete are affected by factors like water-cement ratio, quality of materials, curing conditions, and environmental exposure. Good control over these factors results in high-quality concrete.

Conclusion

Hardened concrete is the final strong and solid stage of concrete that provides structural strength and durability. Its quality depends on proper handling of fresh concrete and curing. Good hardened concrete ensures safe and long-lasting construction.