Dear participants, hey. It's a pleasure to meet you again for this new technical session. I'm JP, Jean-Pascal Planche, and the Vice President for Asphalt and Petroleum Technologies at the Western Research Institute in Laramie, Wyoming in the US. In this video, I will share with you some information of the energy of bitumens. The purpose of this video session is to teach some of the principle of material deformation as they relate to bitumen. We will go over how bitumen responds under different conditions of temperature and loading, and apply rheological concepts to better understand them. We will explore the meaning of stress, strain, modulus and phase angle in viscoelastic materials. Then we will discuss how low or high temperatures and rates affect these properties. Finally, we will see how the use of basic rheological concepts to evaluate the bitumens such as time-temperature superposition, and materials. When an elastic solid is subjected to a shearing force, the stress is proportional to the displacement called strain. The concept of proportionality is called the modulus, and this is similar to the viscosity of liquids. In viscous fluids however, stress is proportional to the rate of the strain. Bitumen is a bit both elastic and viscous quantities, so they are viscoelastic materials. Viscoelastic materials they have an elastic modulus which corresponds to in-phase deformation, as well as the viscous modulus corresponding to out-of-phase deformation. The complex modulus is the vector sum of the elastic and the viscous modulus. The angle of the triangle formed mathematically by this expression is called the phase angle. Delta represents the offset between an applied stress and the resulting strain movement. To intuitively understand the effects of temperature, and loading time, or rate, imagine a ball of silly putty. At relatively hot temperature, if you move it slowly, the modulus decreases. This means the putty feels soft and easily flows like a viscous liquid. The bitumen sample in the tin above room temperature is soft and flows under its weight, just like the silly putty. I tried it with cold temperatures, or if you apply force quickly the modulus increases. This means that putty feels stiff and can bounce back like an elastic solid. Bitumens generally behave similarly to silly putty in these ways, the bitumen sample shown on the picture is hard, stiff and brittle. It does not flow under its weight and is elastic just like the silly putty. We can take advantage of the fact that lowering temperature and increasing loading rate both have similar stiffening effect on bitumen, and vice versa. To do this, the bitumen is measured over a wide range of practical loading time at multiple temperature isotherms. The direct curves from the extra isotherms are then shifted mathematically to line-up with pre-chosen temperature curve. The resulting direct curve is called a master curve. The master curve extends into ranges that may have been untestable due to physical equipment or time limitations. Generally, bitumens follow the so-called time-temperature superposition principle, where time, or frequency, and temperature have a similar impact on the material. This concept is widely used in other areas like in the polymer field. Master curves play a key role in the rheological analysis of bitumens. For example, the modulus master curve indicates how a bitumen stiffness will change through the seasons with the environmental temperature. Bitumens are known to be among the most temperature susceptible materials, with the stiffness going from pascals to megapascals in less than 100 degree sea temperature range. The phase angle of master curve can mould the bitumen's behavior from practically elastic to primarily viscous. These changes are ultimately used to predict the performance of asphalt under the major types of distresses that they experience in the road, thermal cracking, fatigue cracking, and rutting. To summarize, we went over the mathematical functions of stress, strain, modulus, and phase angle as they relate to bitumens. Then, we saw how varying temperature and loading rate can have the same effect on the viscoelastic response. These phenomena are using time-temperature superposition to generate master curve that extend data beyond physical limitations. Finally, we saw how the wide range of data in the master curve is used to predict field performance of asphalts. Thanks a lot for your attention. I hope you had fun watching. And we'll soon see you for another session.