Elastic Modulus of concrete:
The modulus of elasticity or “Young’s Modulus” is defined as the slope of the stress-strain curve within the proportional limit of a material. For a concrete material, the secant modulus is defined as the slope of the straight line drawn from the origin of axes to the stress-strain curve at some percentage of the ultimate strength. This is the value most commonly used in structural design.
Since no portion of the stress-strain curve is a straight line, the usual method of determining the Young’s Modulus is to measure the tangent modulus, which is defined as the slope of the tangent to the stress-strain curve at some percentage of the ultimate strength of the concrete as determined by compression tests.
From the figure we can see that the secant modulus is almost same to the tangent modulus obtained at some lower percentage of the ultimate strength.
Significance of elastic modulus of concrete:
The elastic modulus of concrete is a very important mechanical parameter reflecting the ability of the concrete to deform elastically. For example, in prestressed concrete structures, elastic shortening of prestressed concrete is one of the main factors contributing to prestress loss.
In addition, in order to make full use of the compressive strength potential, the structures using high-strength concrete tend to be slimmer and require a higher elastic modulus so as to maintain its stiffness. Therefore, knowledge of the modulus of high-strength concrete is very important in avoiding excessive deformation, providing satisfactory serviceability and achieving the most cost-effective designs.
Reference : Final Report by Mang tia, Yanjun Liu, In may 2005, Department of civil and coastal engineering, University of Florida, Gainesville, Florida.