A Study on the Effect of Milling on Stress Distributions in Asphalt Pavements

Milling is an indispensable process in recycling of asphalt pavements. The process involves the fracture and removal of asphalt mix under high stress and rapid loading conditions. An understanding of milling induced stress is important for avoiding or reducing the impact on pavements below the milling line and to optimize the milling process. The objectives of this research were to develop a finite element model of the milling process and estimate stress distributions under different milling conditions. Milling of a fine and a coarse graded Hot Mix Asphalt (HMA) and a Stone Matrix Asphalt (SMA) were modeled for different milling speeds and depths. The results indicate significantly high milling induced stresses below the milling line. Gradation of mixes, interface and milling speeds have significant effect on stiffness and hence stress distributions and maximum stresses. The inference is that the depth of milling should be decided on the basis of existing conditions which include layer depths, location of interface, strength of bond between the layers, type of mix, temperature of mix and milling speed (drum rotation speed). To avoid high stress related damage to remaining pavement layers, milling to partial depth of a layer should be avoided. Research is needed to evaluate changes to the structural condition of remaining pavement due to milling.