# MODULUS OF ELASTICITY OF CONCRETE IN COMPRESSION 2020

## STATIC MODULUS OF ELASTICITY OF CONCRETE IN COMPRESSION

## Scope

This test method covers the determination of the chord modulus of elasticity (Young’s) and Poisson’s ratio of molded concrete cylinders and diamond-drilled concrete cores when under longitudinal compressive stress. (ASTM C469).

## Significance

This test method provides 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.

## Apparatus

Compression Testing Machine, Compressometer, Extensometer, Specimen, 6” x 12” Moist-cured concrete cylinders (capped). MODULUS OF ELASTICITY OF CONCRETE.

## MODULUS OF ELASTICITY OF CONCRETE Procedure

- Perform an unconfined compression test on companion specimens in accordance with ASTM C39. The specified loading rate is 35 psi/s.
- Attach the compressometer/extensometer to the test specimen.
- Place the specimen, with the attached compressometer/extensometer, on the lower plate of the test machine.
- Carefully align the axis of the specimen with the centerline of the upper thrust block of the crosshead.
- Lower the crosshead down until contact is almost made with the specimen.
- Zero the dial gages.
- 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 seating of gauges.
- Zero the dial gauge.
- 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).
- 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 e_{1} is the eccentricity of the compresometer pivot rod from the axis of the specimen and e_{2 }is the eccentricity of the longitudinal dial gage from the axis of the specimen. If these eccentricities are equal, then I=0.5. The gage 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 σ_{2}
is the stress corresponding to 40% of ultimate load, σ_{1} the stress
corresponding to a strain of 0.00005, and ε_{2} the strain at a stress
of σ_{2}.

- Calculate: Poisson’s ratio (ν) = (ε
_{t2 }– ε_{t1}) / (ε_{2 }– 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).

## Precautions

- The rate of loading must not differ from the specified value.
- Plot the stress-strain curve with stress on the y-axis.
- Note the readings carefully.

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