Modelling the interaction of road milling machine working elements with heterogeneous layers of asphalt concrete pavement

Abstract

Cold milling of worn pavement is performed on a mass composed of layers differing in composition and in the degree of ageing, while the loads on the working element are calculated from the averaged cutting resistance of the removed material. The discrepancy between the averaged and the stratified formulations has not been quantified, which leaves open the question of whether averaging is admissible when selecting the milling regime and when calculating the strength of the pick mounting. The aim of the work is a quantitative assessment of how the layered heterogeneity of asphalt concrete pavement and local hardened zones affect the force, energy and dynamic characteristics of the milling drum. An author's computational model relates the instantaneous chip thickness, the depth of the removed material and the indirect tensile strength to the tangential force on the pick, the torque and the specific energy consumption; the stochastic part rests on 20 000 realisations. Averaging the strength over the milled thickness underestimates the peak load on the pick by 6.9-18,9% at depths of 70-130 mm and hardly distorts the energy consumption, where the discrepancy stays within 1,4%. Local hardened zones increase the peak force by a factor of 2,1-2,5 and raise the dynamic factor of the torque from 1,09-1,16 to 1,28-1,43, with the maximum at a depth of 70 mm. Energy consumption is governed by pavement temperature and pick wear flat, the loading of an individual pick by the spatial heterogeneity of the material, and merging these tasks within one averaged calculation is incorrect.