BS EN 772-18-2011 pdf download.Methods of test for masonry units Part 18: Determination of freeze-thaw resistance of calcium silicate masonry units.
3 Principle
Calcm silicate masonry units are conditioned by immersion in water in a prescribed way and are then subjected to repeated cycles of freezing and thawing. Damage is assessed visually. Foc samples where visual damage is apparent the compressive strength of the units can be compared with similar samples that have not been subjected to the freeze-thaw regime.
4 Symbols
R is the reduction in strength (%);
is the compressive strength of the sample that is set aside, (N/mm2);
Is the compressive strength of the sample that is subjected to the freeze-thaw cychng, (N/mm2):
N is the total number of freeze-thaw cycles.
5 Apparatus
Freezing cabinet, of net effective volume at least five times that of the volume of the samples to be tested and wtiich is capable of developing an even air temperature of -15 °C in between 3 h and 5 Ii.
6 Sampling
6.1 Sampling
The method of sampling shall be stated in the test repoct. The minimum number of specimens shall be as given in 6.2 below, but a larger minimum number may be specified in the product specification, in which case that larger number shall be used.
6.2 Specimens for freeze-thaw testing
For units with a length ≥ 500 mm and/or height ≥ 300 mm, a total of three units is required from which representative portions may be cut In accordance with B.3 of EN 771-2:2003.
7 Procedure
Mark any damage that may have been sustained by the specimens prior to the test.
Immerse the specimens in water at 20 °C ± 5 °C oriented so that the longest dimension of each Is in the vertical plane. Initially immerse to about one quarter of their height and in such a way that water can circulate freely on all sides.
After I h, immerse the specimens to about half the height of the specimens and after a further 1 h to three- quarters of their height.
After 24 h, immerse the specimens fully in water. After a further 24 h remove them from the water or drain the water and then commence the freezing cycle with the specimens in the same position.
Regulate the air temperature in the freezing cabinet so that it drops gradually in 3 h to 5 h to -15 °C. Maintain this temperature for at least 2 h. After the freezing cycle, thaw the specimens by immersing them fully in water at a temperature of 20 0C ± 5 °C for at least 1 h.
Subject the specimens to the number of freeze-thaw cycles corresponding to the freeze-thaw category specified by the manufacturer, as described above.
Note any visible damage to the specimens under the following categories:
— loss of flatness. e.g. bulging of the surface of the specimens;
— cavities in excess of 5 mm diameter; cracking of the specimen (e.g. surface Cracking).
Ignore all previously marked damage. Evaluation of damage due to freezing and thawing shall be done only on the sides of the specimens that were not created by cutting.
If the specimens do not exhibit any damage in any of the above-mentioned Categories the testing may be terminated
When damage is noted, determine the compressive strength of the specimens that have been subjected to the freeze-thaw cycles and of those which have been set aside (see Clause 6) in accordance with EN 772-1.
8 Evaluation of results
Report any visual damage following the freeze thaw cycling. Calculate the reduction in compressive strength caused by the freeze-thaw cycling of the specimens where some or all were damaged from the untreated specimens set aside (see 6.2) as follows:
If the specimens do not exhibit any damage In any of the above mentioned categories and the testing is terminated R may be taken as R < 20 % (by proxy visual assessment of damages, without calculation)
9 Test report
The test report shall include:
a) name, title and date of issue of this European Standard;
b) name of the organization that carried out the sampling and the method used:
c) date of testing;
d) type, origin and designation of the masonry unit by reference to EN 771-2 induding whether facing or non-facing;
e) number of specimens in the sample:
f) date of delivery of the specimens to the testing laboratory
g) date of preparation of the specimens and the date of test;
h) the total number of freeze —thaw cycles to which the specimens were subjected;
i) a deschpton of any visual damage, after freeze-thaw cling, in accordance with Clause 7 or a statement that no damage has occurred;
j) mean compressive strength of the specimens that have been subjected to freeze- thaw cvling. If necessary
k) mean compressive strength of the specimens that were set aside, if necessary
I) reduction in mean compressive strength. expressed as a percentage, to the nearest percent and whether the result was achieved by calculation or by proxy visual assessment of damages:
m) remarks, If any.BS EN 772-18-2011 pdf download.