BS EN 12370-2020 pdf free download.Natural stone test methods — Determination of resistance to salt crystallisation
7 Preparation of specimens
7.1 Sampling The sampling is not the responsibility of the test laboratory except where specially requested. At least six test specimens, which are considered representative of the body of stone being tested, shall be selected.
7.2 Dimensions of test specimens Cubes of (40 ± 1) mm sides shall be prepared. Specimens shall be wet diamond sawn and any surface irregularities removed by grinding.
7.3 Washing All loose material shall be washed from the surface of the specimen using potable water.
7.4 Drying The specimens are to be dried in an oven at a temperature (105 ± 5) °C until a constant mass is reached. This is assumed to have been attained when the difference between two weighings at an interval of (24 ± 2) h is not greater than 0,1 %. They are then allowed to cool to room temperature and weighed to ± 0,01 g (M d ). Each specimen is then labelled with a durable tag that is wired on to the cube. The specimen is then re-weighed to ± 0,01 g (M d1 ).
8 Procedure The procedure entails the use of a 14 % solution of sodium sulphate decahydrate. The density of the solution shall be checked prior to use. The solution shall only be used for one test cycle. Each of the dried specimens is placed in a 250 ml container and covered with the sodium sulphate solution to a depth of (8 ± 2) mm above the top of the specimen and the container is covered to reduce evaporation. Alternatively, the specimens may be placed in a single container provided that there is a minimum space of 10 mm between specimens and at least 20 mm between the specimens and the sides of the container. The specimens are then left to soak for 2 h at (20 ± 0,5) °C. NOTE Changing the soaking temperature can markedly affect the results.
After immersion the specimens are removed from the solution and dried in an oven. The oven shall be arranged to provide a high relative humidity (90 %) in the early stages of drying and to raise the temperature of the specimens to (105 ± 5) °C in linear progress of temperature change in not more than 15 h. The initial high relative humidity may be obtained by placing a tray of water in the cold oven, and switching on the heater for (30 ± 5) min before putting in the specimens.
The volume of water in ml placed in the tray should be (2,5 ± 0,5) ml for each litre of oven volume. For example (300 ± 25) ml has been found to be adequate in an oven with a 125 l which is capable of holding 48 specimens. The specimens are left in the oven for at least 16 h and then they are cooled at room temperature for (2,0 ± 0,5) h before resoaking in fresh sodium sulphate solution. The cycle of operation is carried out 15 times in all, except when the specimens break up before this. After the 15th cycle the specimens are removed from the oven and stored for (24 ± 1) h in water at (23 ± 5) °C, finally, they are washed thoroughly with flowing water. The specimens are weighed after drying to constant mass (as in 7.4) if they are sufficiently coherent. If the test is to be interupted at any time, the specimens are to be left in the oven at (105 ± 5) °C.
9 Expression of results
The results are expressed as relative mass difference ΔM (mass loss or gain) as a percentage of the initial dry mass M d or as the number of cycles required to induce failure if the specimen has disintegrated or has broken into two or more pieces none of them representing more than 75 % of the sample before the final drying.
If failure has occurred or the specimen has fractured during testing, then this shall be recorded together with the number of completed cycles of testing.
A photographic record of the initial and final condition shall be made.BS EN 12370 pdf download.