In Finland, Round-robin tests have been organized annually for accredited concrete testing laboratories. In 2024, compressive strength and slab test for salt freeze-thaw resistance were tested. Totally 15 testing units participated in the compressive strength testing and 8 testing units in the slab test.<\/p>\n\n\n\n
In the compressive strength testing, readymix concrete having the strength class of C30\/37, the maximum aggregate size of 18 mm and slump class S3 was used. Three individual test results were rejected because of clearly erroneous results. The average compressive strength was 34,6 MPa (cylinder strength) and the standard deviation 1,28 MPa. The coefficient of variation was 3,7 %. Based on the results it was estimated that the margin of the error with C30\/37 would be app. \u00b1 1,3 MPa. The average density of the test specimens was 2355 kg\/m3<\/sup> and the standard deviation 7,9 kg\/m3<\/sup>. Generally, both the variations of compressive strength and density can be considered low.<\/p>\n\n\n\n