Properties of Hardened Concrete
- Modulus of Elasticity
- Water Tightness
When we refer to concrete strength, we generally talk about the compressive strength of concrete. Because concrete is strong in compression but relatively weak in tension and bending.
Concrete compressive strength is measured in pounds per square inch (psi). It mostly depends upon amount and type of cement used in concrete mix. It is also affected by the water-cement ratio, mixing method, placing and curing.
Concrete tensile strength ranges from 7% to 12% of compressive strength. Both tensile strength and bending strength can be increased by adding reinforcement.
Deformation of a concrete structure under sustained load is defined as the concrete creep. Long term pressure or stress on concrete can change its shape. This deformation usually occurs in the direction the force is applied.
Durability might be defined as the ability to maintain satisfactory performance over extended service life. The design service life of most buildings is often 30 years, although buildings often last 50 to 100 years. Most concrete buildings are demolished due to obsolescence rather than deterioration.
Different concretes require different degrees of durability depending on the exposure environment and properties desired. Appropriate concrete ingredients, mix proportions, finishes and curing practices can be adjusted on the basis of the required durability of concrete.
Shrinkage is the volume decrease of concrete caused by drying and chemical changes. In other words, the reduction of volume for the setting and hardening of concrete is defined as shrinkage.
Modulus of Elasticity:
The modulus of Elasticity of concrete depends on the Modulus of Elasticity of the concrete ingredients and their mix proportions. As per the ACI code, the modulus of Elasticity can be calculated using the following equation:
Ec = 33ωc1.5√f’c (psi)
Where, ωc = unit weight of concrete, lb/ft2
f’c = 28 days compressive strength of concrete
For normal weight concrete (90 lb/ft3 to 160 lb/ft3), we assume the formula as
Ec = 57000√f’c
Another property of concrete is water tightness. Sometimes, it’s called impermeability of concrete. Water tightness of concrete is directly related to the durability of concrete. The lesser the permeability, the more the durability of concrete. Now the question is, what is the permeability of concrete?
In simple word, the capability of penetrating outer media into concrete is the permeability of concrete. Outer media means water, chemicals, sulphates, etc.
These are the properties of hardened concrete. You can know about the properties of fresh concrete too by clicking on the link.