Geotechnical Properties of Sand-Asphalt for Use in Road Base Layer Instead of Conventional Materials

Abstract

The study of the geotechnical properties of sand-asphalt for use in road base layer instead of conventional materials, for low to moderate traffic volume, is based on standardized laboratory tests. Sand samples were taken from Kayar, Darou Alpha and Keur Morry (Thies region, Senegal). Identification tests (particle size distribution and sand equivalent) made it possible to select Kayar and Darou Alpha sands which have respective sand equivalent (ES) values of 92 % and 62 %. These values are higher than the minimum required (40 %), for sand-asphalt, with different 35/50 bitumen dosages. The results of the Hubbard-Field test carried out showed that Darou Alpha sands are suitable, with an optimum dosage of 7 % bitumen : the stability at 18 °C, at dry conditions, is 2 732 kg and is greater than the minimum required value of 2 300 kg; the immersion/compression ratio is 85 % and is greater than the minimum required limit of 75 %; water absorption reaches 5.4 % and remains below the maximum required limit of 7 %; the volumetric swelling is 2.6 % and is below the maximum required limit of 5 %. The compactness is 84 % and is acceptable because it exceeds the minimum required limit of 80 %. The sizing carried out with the Alizé©3 software gives deformation values lower than the permissible values. The pavement structure that is placed on a PF3 type platform is therefore correctly sized to support a traffic of 150 heavy vehicles per day for a service life of 15 years. This roadway structure, which is devoid of a foundation layer, includes a 23 cm thick sand-asphalt base layer on which rests a 5 cm thick asphalt concrete. Keywords: sand-asphalt, Hubbard-Field test, Kayar, Darou Alpha, Keur Morry.