[MUSIC] Hello, I'm Emmanuel Chailleux, we met before when presenting the Algoroute project with Clemence Queffelec. I work as a researcher at the French Institute of Science and Technology for Transport, Development and Networks. The objectives of this new video is to understand what are the key challenges for the research and innovation applied to bitumen. First, we will define the research needs related to pavement construction and bitumen production. Then, we will define what could be a performance for bitumen. Finally, some examples of new performancial test developed recently will be presented. In order to build a durable pavement layer, materials which compose a bituminous mixture have to be carefully chosen. Indeed, each road is a unique fabrication tailored for each specific case. In road construction industry, it is not possible to make several prototypes. The structure for several kilometers has to be perfect upon the completion of the construction and for several years. In order to reduce the risk of premature distress, it is necessary to access the performances of materials before the construction, in particular for bitumen. Specificity of bitumen is dependent upon the crude oil origin and the manufacturing process. Moreover, additives are more and more frequently added to plain bitumen to improve performances, how to reduce mixing temperature. In case of recycling, it's a blend composed of the virgin and the recycled bitumen which has to be considered. Bitumen properties must be selected carefully for each specific case. To achieve this, properties related to in-field use have to be measured in lab. It should be underlined that it is useful for development purpose to work also on the property links between the bitumen and the asphalt mixture. Given this technical situation, scientific research has to move towards two types of innovative tests. Mechanical performance tests, on one side. And molecular structure characterization tests, on the other side. In the following, the sequence will focus on mechanical performance tests by giving some examples. What means performance test? The term performance is in contrast to empirical test. As an example, penetrability and self-turning point, which are considered as empirical test, give both indications on the consistency of a bitumen, but are not strictly linked to the pavement properties, the performance of the asphalt mix. On the opposite, linear viscoelastic measurements can provide properties linked to an actual performance on-site. Indeed, as it can be seen on the figure, where complex modulus of a bitumen and the corresponding mix are plotted in the black space. Mix complex modulii of asphalt mixes are derived from those of bitumen. Therefore, for specific aggregate structure and void content, complex modulus of the binder can be used to design an asphalt mix with a given stiffness. Measuring the complex modulus of a bitumen makes sense since the same property is used to design a pavement structure. Especially with the French pavement design method. Linear viscoelasticity theoretical framework is well adapt to define bitumen performances. With a wide range of loading conditions that are different temperature and frequencies. However, distress mechanism observed onsite such as thermal cracking, fatigue on rutting, shows that materials are also loaded out of the linear domain in the last strain domain. In these cases, it has been shown that linear viscoelastic properties are not well adapt to predict performance of all binder as it is shown on the figure where BBR critical temperature is plotted according to observed cracks. Binder performances are intrinsic properties, which could be linked to the pavement loading conditions. They could be assessed using linear viscoelasticity when pavement structure remains under a loading in the small strain domain. As soon as resistance to a distress mechanism like cracking or rutting must be assessed test involving high strain domain, is needed. Some innovative test have been proposed to improve the productivity of performances of asphalt mixes. I would like to present now two example in this video. The multiple stress creep and recovery test has been recently developed and related to rutting resistance. Instead of loading a sample in the small strain domain, the dynamic shear rheometer applies a repeated shear stress which leads to the accumulation of strain. This effect is closer to loading conditions occurring during the rutting phenomenon. Criteria from MSCR test on in-field performances are well correlated as it can be shown on the graph where compliance is plotted according to rutting ALF. For thermal cracking which occurs under low service temperature conditions, test inspired by fracture mechanics concepts have been developed with the idea to study crack propagation involving high strain purview at the crack tip. It allows a better prediction of cracks in the field as shown by Simon Esp and presented on this figure. It also allows to better discriminate between high performance binders and conventional binders. In the table, an example is shown where linear viscoelastic properties from BBR, Bending Beam Rheometer, is unable to make difference between a pure bitumen and the corresponding polymer modified bitumen. In this case, parameters from the fracture mechanic test where the sample is loaded in a high strain domain are able to capture the polymer effect on the cracking resistance. In conclusion, performance tests should be carefully chosen in order to have access to bitumen properties which makes sense as a pavement full scale. Intrinsic properties have to be measured in order to be able to compare pure binder and modified binders with polymer or other additives. Both laboratory and field studies are needed to choose the relevant performances. Reminder of the key points present are. One, new tests on bitumen, able to give the real performances of the asphalt mix are needed to select the appropriate bitumen for specific use. Two, these performances can be based on linear viscoelastic measurements. Three, however, in some cases, specific properties cannot be adequately defined with linear viscoelasticity behaviour, especially when high strain behavior is involved in a distress mechanism. Four, innovative test using fracture mechanics on non-linear viscoelasticity principles are much more appropriate. Thanks for your attention. [MUSIC]
