Practical Realization of a New Concept for Asphalt Compaction

Abstract

Australian field trials of the asphalt multi-integrated roller (AMIR) compactor confirmed the findings of Canadian trials. Consequently a successor to AMIR, hot-iron process asphalt compaction, was designed, fabricated, and tested in 1998 in Australia. With this technology, asphalt mixes can be compacted to equal or greater density with fewer passes than with conventional rolling. Furthermore, there is less variation in density, roller-induced cracking is eliminated, in situ permeability is much lower, and tensile strength and fatigue life are significantly higher. What occurs during the compaction of asphalt concrete mixes is described. The key to this concept is how the binder acts as a lubricant and how the granular particles are reoriented during compaction. Because of significant behavioral differences between unbound granular materials and asphalt concrete, it is suggested that asphalt compaction methods that emulate compaction of unbound granular materials are fundamentally flawed. It is proposed that the behavior of asphalt concrete during compaction may be more accurately modeled with consolidation theory, much like a fine-grained soil. Asphalt compaction is then a fluid flow problem, not the simple particle reorientation required for unbound material compaction. Therefore, the best way to achieve optimum compaction is to supply pressure over a sufficient interval of time. How fluid flow, air flow, and associated particle orientation work together to develop the desired asphalt service characteristics through pressure, contact area, temperature, and load duration are described. Results of analytical and field investigations are presented to support the proposed consolidation-fluid flow model of asphalt compaction.