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Unformatted text preview: ig so that the caps formed have true plane surfaces. Care
shall be taken to ensure that the sulphur compound is not over-heated
as it will not then develop the required compressive strength. Sulphur
caps shall be allowed to harden for at least 2 hours before applying the
2.11.3 Hard Plaster — Just prior to testing, specimens may be capped
with hard plaster having a compressive strength of at least 420 kg/sq cm
in one hour. Such plasters are generally available as proprietry
material. The cap shall be formed by means of a glass plate not less than
13 mm in thickness, having a minimum surface dimension at least
25 mm larger than the diameter of the mould. The glass plate shall be
lightly coated with oil to avoid sticking.
NOTE — Ordinary plaster of paris will not serve the purpose of the capping
material due to its low compressive strength. 2.11.4 As soon as possible after the concrete is mixed, a mortar shall be
gauged using a cement similar to that used in the concrete and sand
which passes IS Sieve 30 but is retained on IS Sieve 15. The mortar shall
have a water/cement ratio not higher than that of the concrete of which
the specimen is made, and shall be of a stiff consistence. If an excessively
wet mix of concrete is being tested, any free water which has collected on
the surface of the specimen shall be removed with a sponge, blotting
paper or other suitable absorbent material before the cap is formed. The
mortar shall then be applied firmly and compacted with a trowel to a
slightly convex surface above the edges of the mould, after which the
capping plate shall be pressed down on the cap with a rotary motion
until it makes complete contact with the rim of the mould. The plate
shall be left in position until the specimen is removed from the mould.
2.12 Curing — The test specimens shall be stored in a place, free from
vibration, in moist air of at least 90 percent relative humidity and at a
temperature of 27° ± 2°C for 24 hours ± ½ hour from the time of addition
of water to the dry ingredients. After this period, the specimens shall be 8 IS : 516 - 1959
marked and removed from the moulds and, unless required for test
within 24 hours, immediately submerged in clean, fresh water or
saturated lime solution and kept there until taken out just prior to test.
The water or solution in which the specimens are submerged shall be
renewed every seven days and shall be maintained at a temperature of
27° ± 2°C. The specimens shall not be allowed to become dry at any time
until they have been tested.
3. MAKING AND CURING COMPRESSION TEST SPECIMEN IN
3.1 This clause deals with the procedure for making and curing
compression test specimens of concrete sampled during the progress of
construction where the nominal maximum size of the aggregate does not
exceed 38 mm.
3.2 Size of test specimen, apparatus to be used and procedure to prepare
specimens shall be the same as specified in 2.
3.3 Curing — The test specimens shall be stored on th...
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This document was uploaded on 10/01/2013.
- Fall '13