TEST SPECIMENS
Eight full size units shall be tested with in 72 hours after delivery to the laboratory, during which time they shall be stored continuously in normal room air.
For the purpose of acceptance, age of testing the specimens shall be 28 days. The age shall be reckoned from the time of the addition of water to the dry ingredients.
CAPPING TEST SPECIMENS
The bearing surfaces of units shall be capped by gypsem. The gypsem and water paste shall be spread evenly on a non-absorbent surface that has been lightly coated with oil. The surface of the unit to be capped shall be brought into contact with the capping paste. The average thickness of the cap shall be not more than 3 mm. The caps shall be aged for at least 2 hours before the specimens are tested.
PROCEDURE
Specimens shall be tested with the centroid of their bearing surfaces aligned vertically with the centre of thrust of the spherically seated steel bearing blocks of the testing machine.
The load up to one-half of the expected maximum load may be applied at any convenient rate, after which the control of the machine shall be adjusted as required to give a uniform rate of travel of the moving head such that the remaining load is applied in not less than one nor more than two minutes.
The compressive strength of a concrete masonry unit shall be taken as the maximum load in Newtones divided by the gross cross sectional area of the unit in square millimeters. Report to the nearest 0.1 N/mm2 separately for each unit and the average for the 8 full units.
Note:- The Gross area is : The total area occupied by a block on its bedding face, including areas of the cavities and end recesses.