Overview
With the change from the old Swiss Standard SN 671 969c, Marshall test, [SN1] to the new European Standards EN 12697-30, Specimen preparation by impact compactor, [EN1] and EN 12697-34, Marshall test, [EN2] the most important change in the test method is the lower compaction temperature. Theere is a research need to made clear the effects of this change.
The effects of the change from the Standard SN 671 969c, Marshall test to the Standard EN 12697-30 and EN 12697-34 are made clear in this study. The statistical investigations conducted allow an assessment of the identified differences.
Funding
Results
Influence on compaction in accordance with EN 12697-30
The bituminous mixtures tested were those with target binder 70/100 (for which the new specified value for compaction temperature is 135°C instead of 145°C) and those with the greatest temperature difference, with target binder 50/70 (new specified value 135°C instead of 155°C). In both cases, the bulk density under [EN1] decreases slightly and as a consequence of the slightly lower compaction the void content increases slightly (0.2 volume-% for target binder 70/100 and 0.35 volume-% for target binder 50/70). The increase is statistically significant. Concerning the quality control of the asphalt production, these slight differences are irrelevant. Purely mathematically, as part of the quality control of the asphalt layers the lower bulk densities of the Marshall specimens compacted in accordance with the new European Standard [EN1] lead to slightly higher compaction ratios for the layers. In certain borderline cases this can lead to the difference that such layers now meet the requirements. In consideration of the slight differences, elevating the requirements of the standard is not necessary.
As part of the project to investigate this matter, an old impact compacter was compared with a new one. Both comply with the standards, but compact differently. It was found that changing the compactor led to differences in results equal in magnitude to those due to changing the compaction temperature.
Influence on Marshall values in accordance with EN 12697-34
Regarding Marshall stability in accordance with [EN2], the measured values decrease slightly (0.6 kN for target binder 70/100 and 1.2 kN for target binder 50/70). This can lead to a different outcome for bituminous mixtures that barely meet the old Swiss Standard when they are tested in accordance with the European Standard [EN1]. Experience to date suggests that the significance of Marshall stability and flow is questionable. Swiss standards thus also set forth requirements only for N and L asphalt mixtures. No requirements exist for mixture types S and H for higher performance grades.
Also investigated was how exchanging an old testing head for a new one influences the results of Marshall stability and flow in accordance with [SN1] and [EN2]. Age, and the associated mechanical wear and deformation of the testing head caused by use, has a significantly greater influence than all other factors. Quality control of the condition and the geometric dimension