Experimental Determination of Modulus of Elasticity of Concrete

The stress – strain relationship of structural concrete under compression is depicted as a 2nd degree polynomial in EN-1992-1. Compressive loads on and the displacements of a 15×30 cm cylindrical specimen, on which a standard compressometer apparatus is mounted properly, are recorded at every 2 ton load increments from the beginning to the failure and beyond. The compressive stresses and strains are computed for all the experimentally obtained points. Many 2nd degree polynomials are fitted by least-squares sequentially first to all the points from the beginning to the maximum stress resisted, and next to other points, each time dropping the highest point, down to the point corresponding to 70% of the maximum stress. Out of so many 2nd degree polynomials, the one with the greatest determination coeffificent is chosen. The slope of the line tangent to that polynomial at 40% of the maximum stress is analytically computed and reported as the tangent modulus of elasticity. The slope of the line passing through the origin and the point on that polynomial at 50% of the maximum stress is analytically computed and reported as the chord modulus of elasticity.