OBJECT: To Determine The Modulus Of Elasticity Of Concrete.
STANDARD:
ASTM C469
APPARATUS:
- Universal Loading Machine
- Compressometer
- Extensometer
- Balance
- Measuring tape or ruller
SIGNIFICANCE AND USE:
- Care must be exercised in the interpretation of the significance of compressive strength determinations by this test method since strength is not a fundamental or intrinsic property of concrete made from give m materials. Values obtained will depend on the size and shape of the specimen, batching, mixing procedures, the methods of sampling, molding, and fabrication and the age, temperature, and moisture conditions during curing.
- The results of this test method may be used as a basis for quality control of concrete proportioning, mixing, and placing operations; determination of compliance with specification; control for evaluating effectiveness of admixtures as similar uses.
- This test method provides a stress to strain ratio value and a ratio of lateral to longitudinal strain for hardened concrete at whatever age and curing conditions may be designated.
- The modulus of elasticity and Poisson’s ratio values, applicable within the customary working stress range (0-40% of ultimate concrete strength), may be used in sizing of reinforced and nonreinforced structural members, establishing the quantity of reinforcement, and computing stress for observed strain.
- The modulus of elasticity values obtained will usually be less than moduli derived under rapid load application (dynamic or seismic rates, for example), and will usually be greater than values under slow load application or extended load duration, other test conditions being the same.
PROCEDURES:
- Weigh the concrete cylinder and determine the average diameter to the nearest 0.1 in (0.25 mm). Cap the concrete cylinder.
- Fix the compressometer and Extensometer to the specimen and attach the dial micrometer in order to measure the deformation of cylinder during loading in compression.
- After the specimens has been set up in the testing machine, apply a slight initial load and set the dial micrometer to read zero.
- Apply load continuously at slow speed approximately 150 ksc/min1 without shock. Record the dial reading of both compressometer and extensometer at about 1000-2000 kg interval. Take care to remove the compressometer and extensometer when the specimen start to crack.
- Plot the load-deformation curve to a suitable scale and determine the following results:
a) Crushing strength or ultimate strength, σc
σc=(4P/πd2)
where P is maximum load and dav is average diameter of cylinder specimen calculated from the diameter measured in two directions at right angles to each other at about mid height of specimen.
b) Compressive stress at elastic limit, σe
σe=0.4(σc)
c) The initial tangent modulus, Ei
d) The tangent modulus at 40% of crushing strength, E
e) The secant modulus at 40% of crushing strength, Es
Es=(σe-σo)/(εe-0.000050)
whereσo is stress corresponding to a longitudinal strain, σo of 50 millionth and εe is longitudinal strain produced by stress σe.