Elasticity of Cement Concrete

Cement concrete is classified as a visco-elastic material. To understand why this is the case, let's first define these terms:

Visco-elastic Material:
A visco-elastic material is one that exhibits both viscous and elastic properties. This means that it can both deform under stress and return to its original shape after the stress is removed. The deformation is time-dependent and the material exhibits a combination of elastic and viscous behavior.

Elastic Material:
An elastic material is one that can deform under stress but is able to return to its original shape once the stress is removed. The deformation is instantaneous, and the material exhibits purely elastic behavior.

Non-elastic Material:
A non-elastic material is one that does not exhibit any elastic behavior. Once it deforms under stress, it does not return to its original shape, even after the stress is removed.

Plastic Material:
A plastic material is one that can deform under stress and retain the deformed shape even after the stress is removed. It does not return to its original shape.

Elasticity of Cement Concrete:

Cement concrete is a composite material made up of cement, aggregates (such as sand and gravel), and water. When these ingredients are mixed together, they form a rigid and solid structure.

However, cement concrete is not a purely elastic material. It exhibits visco-elastic behavior due to the presence of water in the mixture. The water in the concrete undergoes a slow process of hydration, which results in the hardening and setting of the material over time.

Visco-elastic Behavior of Cement Concrete:

The visco-elastic behavior of cement concrete can be observed in its response to stress. When a load is applied to concrete, it initially deforms elastically, meaning it undergoes temporary deformation. Once the load is removed, the concrete is able to recover its original shape.

However, if the load is applied for a longer duration, the concrete starts to exhibit a time-dependent deformation known as creep. This creep deformation occurs due to the viscous properties of the water in the mixture. The deformation increases with time and can become permanent if the load is sustained for a long period.

Additionally, cement concrete also exhibits a phenomenon called stress relaxation. This means that when a constant deformation is applied to the concrete, the stress required to maintain that deformation gradually decreases over time. This is another characteristic of visco-elastic materials.

Conclusion:

In conclusion, cement concrete is classified as a visco-elastic material due to its ability to deform elastically under stress and exhibit time-dependent deformation (creep) and stress relaxation. It is not purely elastic or plastic as it can both recover its original shape and undergo permanent deformation depending on the duration and magnitude of the applied load.