STATIC MODULUS OF ELASTICITY OF CONCRETE IN COMPRESSION
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).
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.
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 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 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 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.
- 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).
- 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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