Question by Govinda D: why we mostly use cylinder and cubes for compressive strength test of concrete?what happen if prism is used?
please wite me about the size effect of testing specimen on its compessive strength.
Best answer:
Answer by Darwin
PRISMS -which we would better call as pyramids, is impractical to use as concrete specimens for testing, because it has no regular cross-section along an axis.
and furthermore, the manufacture of pyramidal concrete specimens is tedious work.. unlike cylinders and cubes.
about the ‘size-effect’ ;it is an ‘unheard-of’ animal in engineering jargon.
note:
testing a concrete specimen for compressive strength is simply applying a specific stress along the centroidal axis of the object under testing.. if the specimen does not fail under such required stress.. it is considered ‘passed’ …a specimen taken from a concrete mixture with the incorrect proportions of ‘cement and aggregates’ is bound to fail this test.
What do you think? Answer below!
Compressive strength test is normally done using cylindrical specimen in order to have an almost constant area throughout the length of the specimen.
Use of cubic samples probably is done ( I don’t know of a test lab for concrete that uses cubes) but this is considered non- standard, because specimens with corners could have stress concentration at the corners and would fail at lower compressive force than a cylindrical specimen of the same area and composition.
The size of test cylinders should be at least 4″ diameter x 8″ long. The preferred size is 6″ diameter by 12″ long. The rule is that the diameter should be at least 3 times the nominal size of the coarse aggregate.
Prisms or samples whose cross sectional area are not constant throughout the length of the sample are not used because of premature failure at the region of the smaller area.