ASTM C78 Standard Test Method for Flexural Strength of Concrete

(Using Simple Beam with Third-Point Loading)

ASTM C78 covers the determination of the flexural strength of concrete by the use of a simple beam with third-point loading

Significance and Use

This test method is used to determine the flexural strength of specimens prepared and cured in accordance with Test Methods C 42 or Practices C 31 or

C 192.

Results are calculated and reported as the modulus of rupture.

The strength determined will vary where there are differences in specimen size, preparation, moisture condition, curing, or where the beam has been molded or

sawed to size.

The results of this test method may be used to determine compliance with specifications or as a basis for proportioning, mixing and placement operations.

It is used in testing concrete for the construction of slabs and pavements

ASTM C78 – Apparatus

The testing machine shall conform to the requirements of the sections on Basis of Verification, Corrections, and Time Interval Between Verifications of Practices .

Hand operated testing machines having pumps that do not provide a continuous loading in one stroke are not permitted.

Motorized pumps or hand operated positive displacement pumps having sufficient volume in one continuous stroke to complete a test without requiring

replenishment are permitted and shall be capable of applying loads at a uniform rate without shock or interruption.

ASTM C78 – Loading Apparatus

The third point loading method shall be used in making flexure tests of concrete employing bearing blocks which will ensure that forces applied to the beam

will be perpendicular to the face of the specimen and applied without eccentricity.

All apparatus for making flexure tests of concrete shall be capable of maintaining the specified span length and distances between load-applying blocks and

,support blocks constant within 60.05 in. (61.3 mm).

The ratio of the horizontal distance between the point of application of the load and the point of application of the nearest reaction to the depth of the beam shall be

1.0 6 0.03. 4.2.3

The load-applying and support blocks shall be maintained in a vertical position and in contact with the rod or ball by means of spring-loaded screws that hold them

in contact with the pivot rod or ball.

The uppermost bearing plate and center point ball  may be omitted when a spherically seated bearing block is used, provided one rod and one ball are used as

pivots for the upper load-applying blocks.

*** Before conducting ASTM C78 , it is important to read the entire specification. Standards can be obtained from appropriate standard authorities.