Recommendations for Low Temperature Cracking

Four binder tests were identified and reviewed as having a potential relationship with asphalt mixture low temperature cracking. The outcomes of these tests are:

1. The BBR test is covered by many papers which indicate that there is generally a good correlation between the BBR limiting temperature and the TSRST failure temperature.

The BBR limiting temperature provides a ranking for the corresponding asphalt’s low temperature behaviour. In contrast to the BBR limiting temperature, BBR stiffness S and m-value determined at -24 °C, are not well correlated with the TSRST failure

temperature, although the latter data was limited to a single paper. With regard to SBS modified bitumen, it is further reported that the BBR test underestimates the low temperature performance.

2. The results of the DTT were found to correlate reasonably well with mixture low

temperature parameters, i.e. derived from TSRST and UTST. Promising candidates for addressing the binder’s contribution to the low temperature behaviour of an asphalt mixture are the failure compliance of the binder, the temperature leading to failure at a specific strain rate and a brittle/ductile transition temperature of binders, designated Tbdb. It has to be noted that the DTT data were from three papers, with each paper addressing different characteristic values of DTT testing correlated with asphalt parameters.

Despite the promising results, the repeatability of the DTT still remains to be improved.

3. The Fraass Breaking Point Test generally has a poor correlation with the asphalt

mixture’s low temperature behaviour besides a bad precision of the test. Therefore, it is not recommended that Fraass breaking point is used to indicate the contribution of the binder towards the performance of asphalt mixtures in respect to their low temperature properties.

4. The data of the Fracture Toughness Test is limited to data from a single paper and, therefore, the binder fracture toughness KIc and fracture energy GIc as performance indicators for low temperature cracking still require further research. The fracture parameters appear to be independent and, thus, may be complementary to other

reasonable low temperature binder properties, for example to parameters from the DTT.

How both types of parameters need to be combined to adequately reflect and predict low temperature behaviour of asphalt mixtures will, of course, need further research.

The repeatability of the binder parameters KIc and GIc still remains to be improved.

From this point of view, the best options for identifying the potential binder contribution to the low temperature behaviour of asphalt are either BBR limiting temperature or a DTT

parameter. An alternative might be the use of the concept of critical cracking temperature, which is a combination of BBR and DTT results to determine a low-temperature parameter called the critical cracking temperature, Tcr. In addition, a “real” fracture property, such as the fracture toughness or the fracture energy, could be used to complement the BBR and DTT results. The critical cracking temperature and fracture toughness both show great promise, but will need time to confirm its suitability and it is unlikely to be available in the immediate future.

There are sufficient data from the papers identified to validate the relationship between BBR limiting temperature of the binder and the mixture’s failure temperature from TSRST

measurements. With regard to both the DTT and the FTT parameters, there is insufficient data from the papers at this time and further research will be necessary before any definitive conclusion can be drawn. Such research should concentrate on the performance

characterisation of modified bitumen. Nevertheless, the durability and any relationship to field performance are effectively missing for all tests. Therefore, there is justification to undertake further research to identify field performance, although such research would take some time to come to a robust conclusion.

6.8 References

[6.01] Forschungsgesellschaft für Straßen- und Verkehrswesen, Arbeitsgruppe Asphaltstraßen: Technische Prüfvorschrift – Verhalten von Asphalten bei tiefen Temperaturen. FGSV 765, 1994.

[6.02] Lu, X, U Isacsson and J Ekblad. Influence of Polymer Modification on Low

Temperature Behaviour of Bituminous Binders and Mixtures. 6^th International RILEM Symposium, 2003 {database ID 263}.

[6.03] des Croix, P. Mechanical fatigue and thermal cracking tests to evaluate pavement performance and comparison with binder properties. Eurobitume & Eurasphalt Congress, Vienna, 2004 {database ID 641}.

[6.04] Guericke, R, and H-E Höppel. ARBIT-Untersuchungsprogramm 1998/99 an 36 Bindemitteln. Bitumen 1/2001 {database ID 700}.

[6.05] Lecomte, M J, G Durand, M Robert and M C Phillips. Examination of the capability of SUPERPAVE tests to predict the low-temperature performance of

polymer-modified binders. Eurobitume & Eurasphalt Congress, Barcelona, 2000 {database ID 514}.

[6.06] Hesp, S A M, T Terlouw and W C Vonk. Low Temperature Performance of SBS-Modified Asphalt Mixes. Association of Asphalt Paving Technologists, 2000 {database ID 241}.

[6.07] Olard, F, H di Benedetto, B Eckmann, J-C Vaniscote. Failure Behaviour of Bituminous Binders and Mixes at Low Temperatures. Eurobitume & Eurasphalt Congress, Vienna, 2004 {database ID 639}.

[6.08] American Society for Testing & Materials. Standard test method for plane - strain fracture toughness of metallic materials. ASTM E 399-90. ASTM, Pennsylvania.

[4.41] Puchard, Z and L Balogh. Duktilitätsprüfung mit Kraftmessung - Erfahrungen in Ungarn.

Bitumen, Heft 1, März 2003.

[4.42] Rogge, D F, C Ifft and L G Scholl. Relating Hot-Mix Properties to Properties of Conventional or Polymer-Modified Binders. Transportation Research Record 1269, 158 {database ID 761}.

[6.09] Lajain, A. Untersuchung des Kraft-Verformungsverhaltens von faser- und

paraffinmodifizierten Bindemitteln mit dem Kraftduktilometer. Bitumen, Heft 4, Dezember 2001.

[6.10] International Standardisation Organisation. Plastics – Determination of fracture toughness – Linear elastic fracture mechanics (LEFM) approach. ISO 13586: 2000.

[6.11] American Association of State Highway & Transportation Officials. Standard Practice for: Determination of Low-Temperature Performance Grade (PG) of Asphalt Binders. AASHTO Designation: PP 42-02.

[6.12] Loibl A, G Lenk, H Mocker and J Stieger. Experience with the performance properties of polymer modified binders used in Austria. Eurasphalt & Eurobitume congress, Vienna, 2004.