Asphalt rutting and its prevention

Abstract

The paper seeks to redress the concerns expressed at the eight Conference on Asphalt pavements for Southern Africa (CAPSA) that the design of hot-mix asphalt did not adequately address prevention of rutting. It presents a consolidation of best practice in the design and application of asphalt layers pertinent to the mitigation of rutting, while being mindful of other performance requirements in terms of fatigue resistance and durability. Two stages of rutting are identified: firstly consolidation and secondly shear deformation. Consolidation is categorised into two phases; that which takes place during construction and that which continues to take place under the action of traffic. Compaction methods for the preparation of laboratory samples should replicate the summation of both these effects for realistic assessment of engineering properties. Recommendations are made in this respect. in addition the effect of mix component characteristics such as aggregate interlock and the viscosity and temperature susceptibility of the binder-filler mastic are examined and indications given on how the composition can be optimised to render the mix rut resistant. Four wheel-tracking test regimens to investigate the propensity of the mix to rutting through shear flow are compared and recommendations made as to the suitability of the methods. Recommendations are made to ensure that the initial state of compaction of the layer will promote further densification under traffic so as to lessen the potential for oxidative hardening with concomitant adverse effects on fatigue resistance and durability. These recommendations cover the required degree of compaction during construction, attention to environmental factors, the effects of mix components and composition and support layers and construction techniques