Long term effect of modified binder on cracking resistance of pavements
Combined loading and climatic effects associated with the choice of high modulus bituminous mixtures, in order to prevent the pavements from rutting, have increased the risk of cracking failure in the bituminous layers. It was decided, in 1989, to start a long-term assessment of a wide range of new products. Cracking, rutting and ravelling monitoring have been carried out regularly during 14 years of pavement service. 16 test sections of 300 meters were constructed. The structures of all those test sections were identical, except the choice of the wearing course binder for which 12 modified binders, and 4 pure bitumens as reference, were selected. A new assessment method of in situ cracking is proposed which consider the gravity and the extent separately in order to get a cracking amplitude parameter. Distinction has been made between the initiation and the propagation of cracking. In general, PmBs show some improvement of the performance of the wearing course compared to conventional binders. However, one section with direct refining pure bitumen performs as well as some PmBs. Cracking resistance for one section with SBS modified bitumen was tremendous. A large amount of tests have been carried out on the wearing course binders and mixes during the whole monitoring period. It was noted that classical laboratory tests couldn't be used as tools for the long term behaviour prediction. Thorough studies were carried out on the TSRST, the BBR tests.