ISO 1920-4:2020 pdf free.Testing of concrete——Strength of hard ened concrete.
4 Determination of compressive strength
4.1 Test specimens
The test specimen shall be: 一a cube or a cylinder in accordance with ISO 1920-3; or
一cores in accordance with ISO 1920-6. Damaged specimens shall not be tested.
Specimens that are badly honeycombed and cracked shall not be regarded as being representative of the quality of concrete supplied. In general, standard cube and cylinder specimens should not be tested if they are badly honeycombed as this is an indication of poor specimen making. When such specimens are tested, the test report shall include the fact that the specimen was honeycombed.
Where the designated size, l or ‘2’ of the cross-section is outside the tolerances, the specimens maybe used for testing by using the actual dimensions; see 4.6.
Where the dimensions or shape of a test specimen exceed the respective tolerances given in ISO 1920-3, the specimen shall be rejected or adjusted (if feasible) by one or more of the following methods:
— uneven surfaces levelled by grinding or by capping;
— the deviation of angles corrected by cutting and/or grinding.
The procedures given in Annex B shall be used to adjust the specimen.
Adjustment by grinding shall be the reference method.
4.2 Apparatus
Thetest shall be carried out using the following:
4.2.1 A compression-testing machine, robust, related to the size of specimen and capable of providing the rate of loading with minimum desired specifications as mentioned in 4.5.1 and 4.5.2. It shall be in calibration at the time of test. The calibration shall be carried out at least once per year.
Accuracy of the test machine shall be such that the percentage error for the loads within proposed range of use of the machine and shall not exceed ±1,0 % of the indicated load.
The compression testing machine shall be provided with a control system. The control system may be operated either by manual or automatic means. If the machine is not equipped with automatic application of force, a pacer shall be fitted to enable the operator to maintain the specified rate. The pacer shall indicate a rate within ±5,0 % of the specified rate.
4.2.2 Machine platens and auxiliary platens, with a hardness value at least 550 HV (Vickers Hardness).
The thickness of the auxiliary platens shall be at least 23 mm. The roughness value, Ru, for the surface texture of the contact faces of the auxiliary platen shall be between 0,4 urn and 3,2 urn.
4.3 Age attest
Tests shall be made at recognized ages of the test specimens, the most usual being 7 days and 28 days. Test at other ages can be performed as per the requirement. The ages shall be calculated from the time water is added to the dry ingredients.
4.4 Number of specimens
At least three specimens, preferably from different batches, shall be made for testing at each selected age.
4.5 Procedure
4.5.1 Preparation and positioning of specimens
For specimens stored in water, excess moisture shall be wiped from the surface of the specimen before placing them in the testing machine. The dimensions of the specimens shall be measured to the nearest 0,2 mm and their weight shall be noted before testing.
The time between the extraction of the specimen from the humidity chamber or the water tank until the test shall be as short as possible and no more than 2 h. The specimen shall be protected from drying while it is outside the humidity chamber or water tank (e.g. by covering with wet burlap).
All testing-machine bearing surfaces shall be wiped clean and any loose grit or other extraneous material shall be removed from the surfaces of the specimen that will be in contact with the platens.
Do not use packing, other than auxiliary platens or spacing blocks, between the specimen and the platens of the testing machine.ISO 1920-4 pdf download.