Trrl Lr 777

A technique in which cores of different wearing-course materials could be inserted in road surfaces was developed to evaluate the performance of a range of bitumens under traffic. At the same time a number of laboratory tests were carried out on the bitumens and it was found that permittivity (dielectric constant) correlkated best with development of texture in rolled asphalt, and that the order of merit was maintained irrespective of the composition of the asphalt and of the traffic carried. It was concluded that petroleum bitumen having a permittivity of 2.650 (25øC, 1.59 kHz) or more will provide a satisfactory texture under any conditions. The test is applicable only to 100 per cent petroleum bitumen. A method has been devised for measuring permittivity accurately