The Study of Effects of the Overheated Bitumen on the Binder Content and the Marshall Properties of the Asphalt Concrete

Road Transport is the major mode of transportation in context of Nepal due to its difficult geographical and geological terrain and also due to the need of huge cost of construction of the infrastructures for the other modes of transportation. The heating of the binder may cause oxidation and stiffening of the binder, hardening of the binder, increase of viscosity and softening temperature. It is necessary to study the influence of overheating on the properties of the bitumen and its impact of the strength of the asphalt concrete. The bitumen binder is heated at different temperatures 1850c, 1950c, 2050c, 2150c, and 2250c for 3-4 hours in an oven and mix design is prepared for each sample at respective temperatures. The study shows that the Marshall Stability value goes on decreasing at increased temperature. Similarly, the OBC and VFB increases as the bitumen becomes less viscous when heated at higher temperature and the aggregate minerals are coated thickly and more voids is filled. The penetration of the overheated bitumen decreases with increase in temperature and the softening point and viscosity of the overheated bitumen also increases as the bitumen is overheated it loses the volatile materials and oxide with oxygen to become stiffer. The Penetration index of the bitumen is found to be more at 2150C. So, the properties of the bitumen changes at higher temperature and will become more brittle and the asphalt mix will be more prone to cracking