In this experiment, we will find out the modulus of elasticity of concrete. An important property of concrete is used to evaluate the stress and strength of concrete. The test method covers the determination of the chord modulus of elasticity (Young’s) and Poisson’s ratio of molded (molded sample) concrete cylinders and diamond-drilled concrete cores when under longitudinal compressive stress. (ASTM C469).
Modulus of Elasticity is defined as the ratio of stress to strain for a material. There are various techniques to find out this property. In this test method stress to strain ratio value and the relation of lateral to longitudinal strain for hardened concrete at whatever age and curing conditions may be specified.
The apparatus used for this test is Compression Testing Machine or UTM, Compressometer, Extensometer, Specimen, 6” x 12” Moist-cured concrete cylinders (capped). MODULUS OF ELASTICITY OF CONCRETE.
MODULUS OF ELASTICITY OF CONCRETE Procedure
The modulus of elasticity is determined from the ration of stress to strain for a material. It can be also calculated from the stress-strain curve obtained from strength test of a material.
- After preparing and setting out the specimen perform an unconfined compression test on companion specimens in accordance with ASTM C39. The specified loading rate is 35 psi/s.
- Then attach the compressometer/extensometer to the test specimen.
- After careful attachment place the specimen, with the attached compressometer/extensometer, on the lower plate of the test machine. In the case of an advanced UTM machine, place the sample directly without the extensometer.
- Now Carefully align the axis of the specimen with the centerline of the upper thrust block of the crosshead.
- Adjust and Lower the crosshead down until contact is almost made with the specimen.
- Set the dial gauges Zero.
- Then Load the specimen at a rate of 35 psi per second (990 lb/s) until a load of40% of ultimate is reached. Stop loading at this 40% value and reduce the load to zero for the seating of gauges.
- Again Zero the dial gauge.
- After that perform the one or two loading cycles and continue the loading until 40% of the ultimate load is achieved, recording without interruption, the applied load, and longitudinal deformation at set intervals (50 millionths).
- Finally, Calculate stress and longitudinal strain as follows:
- Stress, σ= P/A
Where P is the applied load and A is the cross-sectional area of the cylindrical specimen.
Strain, ε= d/Lo
Where d is the longitudinal specimen deformation and Lo is the gage length.
The deformation, d is equal to
d = gI
Where g = longitudinal dial gauge reading and
Where e1 is the eccentricity of the compresometer pivot rod from the axis of the specimen and e2 is the eccentricity of the longitudinal dial gage from the axis of the specimen. If these eccentricities are equal, then I=0.5. The gauge length is the distance between yokes.
- Plot the stress-strain curve (stress on the ordinate and strain on the abscissa).
- Calculate E to the nearest 50,000 psi as follows:
Where σ2 is the stress corresponding to 40% of ultimate load, σ1 the stress corresponding to a strain of 0.00005, and ε2 the strain at a stress of σ2.
- Finally Calculate: Poisson’s ratio (ν) = (εt2 – εt1) / (ε2 – 0.00005)
- After loading to 40% and recording the load versus displacement data, unload the specimen.
- Remove the compresometer (the compresometer may be left in place when appropriate to generate the entire stress vs. strain curve to failure).