Length of the broken portions of the beams selected

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Unformatted text preview: — The length of the broken portions of the beams selected for the compression test shall be at least 5 cm greater than the depth of the beam and the broken portions shall be free from cracks, chipped surfaces or other obvious defects within the length to be tested. 6.4 Procedure — During the interval between testing the specimens as beams and testing the broken portions as cubes, the specimens shall be stored in water at a temperature of 24° to 30°C and shall be tested immediately on removal from the water and while still in the wet condition. 6.4.1 Placing the Specimen in the Testing Machine — The bearing surfaces of the testing machine and the bearing plates shall be wiped clean and any loose sand or other material shall be removed from the surfaces of the specimen which are to be in contact with the bearing plates. The specimen shall be placed between the bearing plates in such a manner that the upper bearing plate is directly over the lower plate and the bearing plates extend at least 25 mm from each end of the specimen. A device which ensures the proper location of the upper plate with reference to the lower plate is shown in Fig. 2. No packing shall be used between the faces of the specimen and the bearing plates. The specimens shall be tested with the moulded sides in contact with the plates. The load shall be applied without shock and increased continuously at a rate of approximately 140 kg/sq cm/min until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained. The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted. 6.5 Calculation — The equivalent cube strength of the specimen shall be calculated by dividing the maximum load by the area of contact of the bearing plates and shall be expressed to the nearest kg/sq cm. 6.6 Report — The following information shall be included in the report on each specimen: a) identification mark, b) date of test, c) age of specimen, d) curing conditions, e) nominal size of specimen, f) maximum load, g) equivalent cube strength, and h) appearance of the concrete and type of fracture, if these are unusual. 13 IS : 516 - 1959 FIG. 2 DEVICE FOR ALIGNING BEARING PLATES 7. MAKING AND CURING FLEXURE TEST SPECIMENS IN THE LABORATORY 7.1 This clause specifies the procedure for making and curing flexure test specimens of concrete in the laboratory where accurate control of the quantities of materials and test conditions is possible, provided the maximum nominal size of the aggregate does not exceed 38 mm. The method is specially applicable to the making of preliminary flexure tests to ascertain the suitability of the available material or to determine suitable mix proportions. 7.2 Sampling of Material — Preparation of materials, proportions, weighing, mixing of concrete shall be done in the same way as in the case of making compression test specimens in...
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