Asphalt concrete is one of the most common types of pavement surface materials used in the world. It is a porous material made at very high temperatures (~180 °C) that consists of a mixture of asphalt binder (bitumen), aggregate particles and air voids. After some years of use, the stiffness of asphalt concrete increases, its relaxation capacity decreases, the binder becomes more brittle, micro-cracks develop in it and cracking of the interface between aggregates and binder occurs. This mechanism is especially detrimental in porous asphalt where it leads to ravelling. Ravelling, which is the loss of aggregate particles from the surface layer, is the main damage mechanism of porous asphalt surface wearing courses. In the chapter “Unravelling of porous asphalt” in this book it is discussed that ravelling can be avoided or delayed by mixing steel wool fragments through the asphalt. These fragments make it possible to heat the asphalt with induction energy and by that close micro-cracks. In this project another approach is followed: the use of rejuvenators. These rejuvenators are encapsulated and mixed through the asphalt. These capsules break due to the constant fatigue loads and to the higher stiffness of the binder that happens when it oxidizes. Once the capsules are broken, a permanent deformation happens in the capsules and if the fatigue loads of traffic continue, they suffer a permanent deformation and the rejuvenator is released and softens the binder and makes it more flexible again. In the project the capsules are optimized and the process of rejuvenation is studied.
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