Modulus of Elasticity, Creep, Shrinkage of concrete and Solution of some Competitive exam question.

Modulus of Elasticity/YOUNGS MODULOS (E) = STRESS/STRAIN.
But concrete is not a homogeneousmaterial So it has different strain value at different time periods.
Concrete is a brittle material and it shows smaller value of strains before failure. Concrete fails suddenly and that is the big disadvantage of concrete in construction. To overcome this effect concrete is mostly use as a reinforced concrete (having steel bars inside). The strain in concrete is of 2 types
ELASTIC STRAINS
Up to some limits strains are reversible (elastic in nature), which recovers while applied stresses are being removed. Plastic strains yield in the specimen before reaching peak point (maximum strains specimen able to bear before failure)
INELASTIC STRAIN:-
It is the change in shape of concrete which can not regained by age of concrete. Eg: Creep, Shrinkage
Concrete creep
is defined as: deformation of structure under sustained load. Basically as long term pressure or stress on concrete can make it change shape. This deformation usually occurs in the direction the force is being applied. Like a concrete column getting more compressed, or a beam.
Shrinkage of concrete:-
decrease in either length or volume of a material resulting from changes in moisture content or chemical changes.
1. Static Elastic Modulus:
The strains obtained as above are plotted against stress and a curve is obtai­ned as shown in Fig. 15.5. As concrete is an imperfect elastic material, stress strain diagram is a curved line. Hence three methods can be used to determine the modulus of elasticity.
(a) Initial tangent modulus.
(b) Tangent modulus.
(c) Secant modulus.
(a) Initial Tangent Modulus:
It is represented by the slope of a tangent to the stress-strain curve drawn passing through the origin. This modulus has significance only for low stresses and thus is of limited value and not easy to determine.
(b) Tangent Modulus:
It is represented by the slope of the line drawn tangent to the stress-strain curve at any point on the curve, but this modulus applies only to very small changes in load above or below the load at which the tangent modulus is considered. Secondly it is difficult to determine tangent modulus with accuracy as the tangent to the curve is drawn by the eye judgment.
(c) Secant Modulus:
It is represented by the slope of a line drawn from the origin to any point C on the curve. This method is most practical and is in most general use as it represents the actual defor­mation at the selected point and no uncertainties are involved in its determination. Secant modulus is found to decrease with the increase in stress hence stress at which it has been determined should be stated.
2. Dynamic Modulus:
The value of modulus of elasticity Ec determined by actual loading of concrete is known as static modulus of elasticity. This method of testing is known as destructive method as the specimen is stressed or loaded till its failure. The static modulus of elasticity does not represent the true elastic behaviour of concrete due to the phenomenon of creep. At higher stresses the modulus of elasticity is affected more seriously.
Thus a non-destructive method of testing known as dynamic method is adopted for determining the modulus of elasticity. In this case no stress is applied on the specimen. The modulus of elasticity is determined by subjecting the specimen to longitudinal vibration at their natural frequency that is why this is known as dynamic modulus.

[@trilochandash2071]

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[@saurabhkumar8884]

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[@shubhamprajapat6887]

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