Laurence Lapalu

Low-Temperature Thermal Cracking of Asphalt Binders as Ranked by Strength and Fracture Properties

The original Superpave low-temperature specification for asphalt binders placed limits on the low-temperature stiffness and m-value. A recently approved alternative to the original Superpave asphalt binder low-temperature specification makes use of the measured stiffness and tensile strength of the binder to determine a critical cracking temperature. Thermal cracking temperatures are presented for 42 plain and modified asphalt binders. Thermal cracking temperatures determined by the original and recently approved alternative Superpave specification are compared. The fracture toughness, KIC, can also be used to evaluate low-temperature cracking properties of asphalt binders. Fracture properties obtained for 14 asphalt binders are compared with the thermal cracking temperatures determined by the original and recently adopted alternative Superpave specifications. The set of 14 binders was produced from a common base material but modified by different means. For the set of 14 binders, there is little difference in their ranking according to both the original and recently proposed alternative Superpave low-temperature criteria; however, their ranking is quite different on the basis of the fracture properties as measured by KIC. KIC appears to provide a much more discriminating ranking of the binders than either of the Superpave specification criteria.

Environmental and mechanical evaluation of warm mix asphalts in laboratory and on site

Warm asphalt mixes made with ready to use binders or with other types of technology like bitumen foam are commonly used in France and elsewhere. In order to develop knowledge on the different technologies, an experimental trial has been organized in September 2013 in partnership between TOTAL Marketing Services, Eiffage TP and Ifsttar. The purpose of the test was to carry out environmental assessment of the warm mixes comparatively to traditional hot mixes. 4 sections have been realized (hot mix asphalt, warm mix asphalt with respectively ready to use binder, foam, and combination of foam and ready to use binder). The asphalt plant had been equipped in order to record energy consumption and to monitor the chimney emissions. On average the different warm mix technologies lead to savings on energy consumption and on greenhouse effect gases. Extensive asphalt quality data like for example voids contents and macrotexture have also been recorded during the trial. Stiffness tests have also been carried out on cores. Performances of warm mixes are equivalent to the ones obtained with hot mix. A follow-up of the test is planned.

Low temperature and aging properites of polymer-modified binders

The search for a “universal” (applicable to any kind of bituminous binder) test describing the performance of bituminous binders at low temperatures is still ongoing. Although several test methods exist, they remain questionable and discussed, be it in relation to their reliability (reproducibility / universality of Fraass testing) or for phenomenological reasons (e.g. no crack phenomenon for BBR testing). Our paper presents the results of a study devoted to the validation of different methods measuring the low temperature behaviour of bituminous binders. This validation was performed in reference to the restrained specimen thermal shrinkage test (TSRST) performed on an standard asphalt mix-design. In addition to both Fraass and BBR testing, a newer method (ABCD test) for the assessment of cracking behavior has been evaluated as well. The investigation focused on pure bitumen and binders modified at several levels of content with an elastomeric polymer. The majority of the modified binders have been obtained by a technique of crosslinking but comparisons were also made with equivalent un-crosslinked physical mixture binders. Finally, an important part of the investigation was devoted to a concomitant analysis of the sensitivity of these test methods to the degree of aging of both binders and asphalt mixes.