Appears to be homogeneous and has the desired

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Unformatted text preview: re batch mixed until the concrete appears to be homogeneous and has the desired consistency. If repeated mixing is necessary, because of the addition of water in increments while adjusting the consistency, the batch shall be discarded and a fresh batch made without interrupting the mixing to make trial consistency tests. 2.7 Workability — Each batch of concrete shall be tested for consistency immediately after mixing, by one of the methods described in IS : 1199-1959. Provided that care is taken to ensure that no water or other material is lost, the concrete used for the consistency tests may be remixed with the remainder of batch before making the test specimens. The period of re-mixing shall be as short as possible yet sufficient to produce a homogeneous mass. 2.8 Size of Test Specimens — Test specimens cubical in shape shall be 15 × 15 × 15 cm. If the largest nominal size of the aggregate does not exceed 2 cm, 10 cm cubes may be used as an alternative. Cylindrical test specimens shall have a length equal to twice the diameter. They shall be 15 cm in diameter and 30 cm long. Smaller test specimens shall have a ratio of diameter of specimen to maximum size of aggregate of not less than 3 to 1, except that the diameter of the specimen shall be not less than 7.5 cm for mixtures containing aggregate more than 5 percent of which is retained on IS Sieve 480. 2.9 Moulds 2.9.1 Cube Moulds — The mould shall be of 150 mm size conforming to IS : 10086-1982*. 2.9.1.1 In assembling the mould for use, the joints between the sections of mould shall be thinly coated with mould oil and a similar coating of mould oil shall be applied between the contact surfaces of the bottom of the mould and the base plate in order to ensure that no water escapes during the filling. The interior surfaces of the assembled mould shall be thinly coated with mould oil to prevent adhesion of the concrete. *Specification for moulds for use in tests of cement and concrete. 6 IS : 516 - 1959 2.9.2 Cylinders — The cylindrical mould shall be of 150 mm diameter and 300 mm height conforming to IS : 10086-1982*. The mould and base plate shall be coated with a thin film of mould oil before use, in order to prevent adhesion of the concrete. 2.9.3 Tamping Bar — The tamping bar shall conform to 6.1(a) of IS : 10086-1982*. 2.10 Compacting — The test specimens shall be made as soon as practicable after mixing, and in such a way as to produce full compaction of the concrete with neither segregation nor excessive laitance. The concrete shall be filled into the mould in layers approximately 5 cm deep. In placing each scoopful of concrete, the scoop shall be moved around the top edge of the mould as the concrete slides from it, in order to ensure a symmetrical distribution of the concrete within the mould. Each layer shall be compacted either by hand or by vibration as described below ( see 2.10.1 and 2.10.2 ). After the top layer has been compacted, the surface of the concrete shall be...
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