Modulus of elasticity of concrete is the ratio of the stress to the strain of the concrete under the application of loads. It is one of the very crucial properties of concrete that gets affected with the influence in concrete strength, aggregate, cement paste, mix proportion, moduli of elasticity of the ingredients, and the characteristics of the transition zone. These factors control and govern the elastic behavior of concrete.

1. Strength of Concrete

Modulus of elasticity of concrete increases approximately with the square root of the strength.

2. Cement Paste

Porosity and elastic modulus of hydrated cement influence the modulus of elasticity of concrete. As porosity decreases, the modulus of elasticity of cement paste increases and, consequently, the elastic modulus of concrete increases. The porosity of cement paste is controlled by water to cement ratio(w/c), air content, admixture dosage and degree of cement hydration.

Cement Paste
Fig. 1: Cement Paste

3. Aggregates

The porosity of aggregate significantly influences the elastic modulus; aggregate with low porosity results in high modulus of elasticity. Larger proportion of coarse aggregate leads to a high value of elastic modulus.

4. Concrete Wetness Condition

It is demonstrated that the modulus of elasticity of wet specimen is greater than that of the specimen that is tested in a dry condition by 15%. This is because the dry condition generates more microcracks in the transition zone and consequently this is explained by the fact that drying produces more microcracks.

5. Transition Zone

The modulus of elasticity declines as the transition zone is weakened due to the existing cracks, orientation of C-H crystals and existing void spaces. The transition zone is the interfacial region between the particles of coarse aggregates and hardened cement paste. 

It is a plane of weakness because the quality of paste in the transition zone is of poorer quality and due to internal bleeding, water accumulates below the elongated, flaky and large pieces of aggregates.

Transition Zone in Concrete
Fig. 2: Transition Zone in Concrete

6. Mix Proportion

It is noticed that higher the amount of cement, higher the modulus of elasticity.

7. Concrete Age

Modulus of elasticity increases as the concrete ages.

8. Curing Regime

For the same strength, modulus of elasticity of steam-cured concrete is slightly lower than that of water-cured concrete.