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BS EN 206:2013 requires testing of concrete for Modulus of Elasticity. What is Modulus Elasticity and why is it important?
Modulus of elasticity is also known as Young's Modulus, Elastic Modulus and the Coefficient of Elasticity. It's value is obtained by dividing stress over strain.
Stress is a result of force (measured in Newton or N in short) applied over a unit of area (measured in mm2 for example) of a material (therefore expressed in N/mm2).
i.e. Stress = force / cross sectional area:
where,
σ = stress,
F = force applied, and
A= cross sectional area of the object.
Strain on the other hand is extension per unit length.
i.e. Strain = extension / original length
where,
ε = strain,
lo = the original length
e = extension = (l-lo),
and
l = stretched length
(Strain has no units because it is a ratio of lengths)
Therefore Modulus of Elasticity is:
Stress/Strain
It is a number which is defined by the ratio of the applied stress to the corresponding strain within the elastic limit. Physically it indicates a material’s resistance to being deformed when a stress is applied to it.
So in essence it indicates the stiffness of a material. In other words, it is how easily it is bent or stretched. Value of elastic modulus is higher for the stiffer materials.
When a material reached a certain stress, the material will begin to deform. It is up to a point where the material's structure is stretching and not deforming. However, if you are to stress the material more than this, the molecules or atoms inside will begin to deform and permanently change the material.
A good analogy to this would be a rubber band: when you stretch a rubber band you are not deforming it, but stretching it. However, if you pull it too hard the rubber band will begin to deteriorate, or deform.
Usually when this happens, it is not too much longer until it breaks.
So, why is Modulus of Elasticity important?
It's because it can be used to predict the deflection that will occur when a load is applied. It can also tell us something about the bond strength between atoms making up the bulk material. The modulus of elasticity is a very important mechanical property of concrete. The higher the value of the modulus, the stiffer the material is.
