Control of Engineering Properties of Asphalt Concrete Based on Permanent Deformation Constraint of Subgrade at Tropical Zones in Iran (TECHNICAL NOTE)

The permanent deformation pavement of roads and streets at tropical zones Abstract (if layers are sufficiently compacted) is due to increase of asphalt layers temperature and consequential decrease of modulus of elasticity. Therefore, the asphalt mixture moves aside of the wheels of heavy vehicles and cause permanent deformations without volume variation. On the other hand, if the asphalt layer modulus of elasticity is not appropriate, additional stresses will be moved to the soil subgrade and thus causes permanent deformation. The materials used for the asphalt layers can be controlled by the proposed method so that additional stresses can be avoided. This study includes three types of pavements (thin, intermediate and thick) on three kinds of subgrades (weak, intermediate and strong) at tropical zones of Iran. Modulus of elasticity and Poisson ratio of layers are selected based on the earlier studies. The heavy axles of vehicles in Iran which cause the most damages are considered in this study (13 tons with two axle trucks). Then the modulus of elasticity of the asphalt mixtures is changed and stress-strain analysis is performed by the Elsym5 computer software to produce the maximum normal strain at the subgrade for all above mentioned types. The number of passing axles used in the analysis is obtained by the formula proposed by the Asphalt Institute (N=1.6×10-9(ε)-4.477). Nomographs showing number of passing axles versus modulus of elasticity for all cases based on the computer analysis are drawn. The designed pavement can be compared to the corresponding nomograph mentioned above to control the modulus of elasticity of asphalt mixtures which prevent the subgrade from additional stresses by using the predicted passing axles.