The Swiss climate is characterised by a broad spectrum of temperatures, making high demands on the right choice of bituminous binders for road construction. They have to fully comply with current and future demands on road pavements in winter as well as in summer. Global warming must not hide the sporadic occurrence of strong winters with extreme low temperatures like in 2008/2009, which lead to embrittled pavements and thermally induced cracks.

The conventional assessment of the low temperature properties of bitumen and bituminous binders is often insufficient and repeatedly results in costly misjudgements and damaged roads. Because the standardised test method “Fraass breaking point” shows a low reproducibility, the search for an alternative test method was initiated. Some years ago, the determination of the flexural creep stiffness with the bending beam rheometer (BBR) was proposed. As this was a creep test, the expectations have only partly been satisfied. At low temperatures mainly crack induced failures were observed, which are better simulated by a fracture test. Possible alternative test methods are:

a) Determination of the fracture toughness by a static fracture toughness test

b) Determination of the DSR-breaking point in a fatigue test with the dynamic shear rheometer (DSR).

Originally, the static fracture toughness test (SFTT) was adopted from the polymer science and was improved and adapted lately to bituminous binders by a task group of the standardisation committee CEN TC 336 WG. Meanwhile the test method is ready to be evaluated in a European round robin test, before it will become a European standard. In order not to be entirely left out of the European standardisation process, it is very important for Switzerland to use this unique opportunity to participate in the imminent European round robin test.

The second test method is based on a binder fatigue test on a DSR at decreasing temperatures until fracture occurs. This temperature at fracture is defined as DSR-breaking point. In principle, the goal of this project consists in refining and validating the test method to obtain reliable and repeatable values. Only afterwards, the significance of the results can be verified.

In the last meeting of CEN TC 336 WG in February it was decided to give SFTT a high priority. Therefore, it is planned to carry out a round robin test already in the second half of 2009, to collect the mandatory precision data.