The Institute of Standard and Industrial Research of Iran is one of the main members of the international organization of standards, which, while paying attention to the general conditions and specific needs of the country, uses the latest scientific, technical and industrial developments in the world and international standards.
The standard of construction stones has been approved in the 61st meeting of the National Committee of Construction Standards and Materials dated 9/18/2000.
- Purpose and scope of application
The purpose of compiling this standard is to determine the coefficient of disjointing of all types of building stones except slate.
- Importance and application
This test method is used to determine the fracture coefficient of different stones and compare stones of the same type.
- Needed tools
Loading device: with the accuracy of the loading device, up to 1% of the loading range is acceptable.
Support: Place the sample on two flat-shaped supports (according to Figure 1). The length of the support must be at least equal to the width of the sample. The supports can be blades or rollers.
- Sampling
- The sample should be selected in such a way that it shows the real average of the type or quality of the desired stone. The sample should be of the same quality that is offered in the market.
- The sample may be selected by the buyer or his authorized representative from the stones extracted or available in the mine. The sample size should be enough for at least three tests.
- When there are noticeable changes, the buyer can choose as many samples as he deems necessary to determine the range of their stiffness coefficient changes.
- The samples should be approximately (100 x 200 x 57) millimeters in size, and their number should be at least three for each loading condition. The samples should be cut from the main sample and its surfaces should be smooth and polished. Its 200 x 100 mm surfaces should be flat and parallel to each other as much as possible. For loading in the direction perpendicular to the layering of the stone, 5 tests should be prepared, the surfaces of which are 100×200 mm parallel to the layering. (Figure 1b)
- To load the test piece parallel to the layering, 5 tests should be selected whose 100x75mm surfaces are parallel to the stone layering.
- To perform the stone test in each of the dry conditions, 10 tests are required, 5 of which are used to perform the test in the direction of layering and the other 5 are used in the direction perpendicular to the layering.
- Reminder – lamination is the direction in which the stone is separated much more easily than in other directions. In layered rocks, the direction of lamination corresponds to any direction of layering.
- Marking and measurement of the test:
- To determine the place of loading and the place of the supports according to figure 1b and c. To determine the place of loading, divide the test piece into two equal parts with a line perpendicular to its length.
- Measure the width of the test piece with an accuracy of 0.25 mm at the place of loading.
- Obtain the thickness of the test piece from the average of three measurements at the loading and support locations.
- Test conditions
– Before performing the test, the samples should be placed in a dry environment or at a temperature of 60+2 degrees Celsius for 48 hours. In the 46th, 47th and 48th hours, the weight of the samples should be measured to ensure its stability. If a decrease in weight is observed, the drying test of the samples is continued until the same result is reached in three consecutive weighing with a time interval of one hour. After removing the samples from the dryer and before the test, they are placed in a desiccator or at the room temperature.
– Before performing the test in wet conditions, the samples should be immersed in water for 48 hours at a temperature of 22+2 degrees Celsius. When removing the samples from the water, they should be free of surface moisture. Immediately after removing the samples from the surface water bath, take them with a cloth and test them.
- Take the test
– The largest surface of the test piece should be placed on the edge of the supports that are about 175 mm apart, and the loading blade should be placed on the test pieces at an equal distance from the supports. The three mentioned blades must be parallel to each other during the test. For this purpose, a load of about 44 Newton should be applied, then the loading and support points should be controlled to match the drawn lines. The loading speed should not exceed 445 until the complete failure of the test.
– Reminder – If the loading blade and the supports of the machine are of the roller type, the upper denominator of the test piece must be completely horizontal on it.
- calculations
The coefficient of rupture of the specimen is obtained from the following equation.
R=3wl/2bd
In which:
R = the rupture coefficient of the Mc Pascal test
W= load at the moment of failure in Newtons
I = Distance between two supports in millimeters
B= Width of the test piece in millimeters
D = The thickness of the test piece in millimeters
- reports
If the test result is more than 20% below the average of all breakage values, inspect the sample. If this value is due to the test being cracked or machine error, discard the results and report the remaining average as the breakage coefficient of the sample. The results should be reflected in the report, the following information should also be reported.
– Specimen specifications include: Name and location of the mine, name and location of the extraction workshop, date of sampling, trade name and grade of stone
– The size and shape of the tested sample and the description of the method based on which the sample was prepared.
