Overview
With the standard delivery Association Internal 99/68 a recommendation for determining the static one-off penetration will be published with a flat stamp. This recommendation clarifies the procedure compared to the currently applicable Swiss standard SN 640 440a and DIN standard 1996 material respects and complies with the current CEN draft.
The current CEN draft (Stage 40) was decisive influenced by Switzerland. The requests included in the VSS recommendation clarifications have already been found in this EN standard design input.
The objective of the project is to determine the comparability and the repeatability of the association's internal recommendation VSS 671 970. This recommendation corresponds to the current CEN draft. The previous method according to SN 640 440a is to be modified.
Funding
Results
The round robin test “Static indentation with a flat stamp” was conducted on mastic asphalt cubes in winter 2000/2001 in accordance with VSS Recommendation 671 970 “Bituminous mixtures; This VSS Recommendation 671 970 was issued in November 1999 and went into effect in January 2000.
In comparison with the previously used method described in DIN 1996 (Part 13), 1976 and adopted in SN 640 440a, several modifications were incorporated into recommendation 671 970, from which one hoped for improvements in repeatability and reproducibility.
The more precise specifications of VSS Recommendation 671 970 were carried over into EN 12697-20: 2003 “Bituminous mixtures - Test methods for hot mix asphalt - Part 20: Indentation using cube or cylindrical specimens” . With the national Foreword SN 670 420, this EN was adopted into the body of Swiss standards on 1 January 2005.
No improvement of uncertainty in measurement was achieved through the round robin test with 13 laboratories, in spite of the use of meticulous test descriptions, an instruction session for the participating laboratories conducted prior to the round robin test, optimally uniform industrially manufactured mastic asphalt for use as testing material, and careful sampling to obtain specimens of the highest possible uniformity.
A standard deviation of repeatability sr of 7.8 to 10.0 % for the mastic asphalt types MA 6, MA 8 and MA 11 was determined. The norms prescribe 10 %. The standard deviation of reproducibility sr ranges from 14.7 to 25.2 %. The norms prescribe 20 %. The values for MA 11 lie above 20 %. When calculating the precision, the standard deviation is multiplied by a factor of 2.8, thus the repeatability and reproducibility also meet the standard requirements with 28 and 55 %. These values for uncertainty in measurement were determined using mastic asphalt types with varying degree of indentation. The mean values after 30 minutes (ET 30) for MA 6, MA 8 and MA 11 are 3.9 mm, 2.2 mm and 1.3 mm.
Because the round robin test results confirmed the previously usual levels of repeatability and reproducibility, further studies were conducted beyond the testing mandate that might indicate potential influencing parameters. In the round robin analysis of “static indentation” on rubber test specimens, which through further investigation proved to be homogeneous, the degree of influence of the test meth- od, including the testing apparatus, was determined to be