Flexible pavement is one of the useful type of pavements in road, so great efforts have been made to increase the efficiency and operation of this type of pavement. Slippery road surface at the time of raining, is one of the parameters which affect road safty and may increase road accident. Existence of water on the pavement surface reduces surface friction. One of the significant factors that reduce friction is the formation of thin layer of water on the surface. One of the ways to improve surface drainage on the road is usage of nano superhydrophobic coating. Unfortunately lack of sufficient research on the use of this material in the road construction industry can be seen. The aim of this study was to investigate the characteristics superhydrophobic coatings, which were compatible with asphalt surface, to improve surface drainage. One of the main methods of detection and evaluation of hydrophobic surfaces is measuring the contact angle. Contact angle of water was measured in the presence of different hydrophobic coatings with specified weight percent of coated materials. The best hydrophobic material was chosen which produced the greatest contact angle on the asphalt surface. A device is also built to measure water velocity at the surface of pavement. The velocity of surface drainage was measured with and without of superhydrophobic coating. The measured contact angles on asphalt samples with eight different hydrophobic materials showed that, a hydrophobic with brand name of W 4 from Golfam company, made the largest contact angle; the average contact angle increase from 74.7 degree to 156.3 degree. The result of measured flow velocity on coated and uncoated pavement surfaces, indicated that average flow velocity on coated pavement is 2.15 and 2.13 times greater than uncoated type 0-12 and 0-19, respectivly. Keywords: Flexible Pavement, Contact angle, Superhydrophobic, Velocity of surface drainage.
