Experimental investigation of Marshall and Superpave mix design methods for rutting criteria

Abstract

Asphalt mix design for tropical high temperature climate regions is challenging, especially, for roads expected to carry heavy truck loads and higher design traffic significantly exceeding 1 million equivalent single axle loads. The main focus, while performing asphalt mix design, in these regions is to ensure that the designed mix is resistant to plastic deformation. Marshall mix design is still the most commonly used procedure in tropical countries. Serious drawbacks with Marshall mix design procedure are its mode of compaction, which does not simulate the field compaction as well as a poor methodology to identify mixes prone to plastic deformations. To evaluate rutting susceptibility, some studies have recommended extending the original Marshall mix design procedure by supplementing it with a minimum void criterion at refusal density. This paper reports on an experimental study aimed at evaluating whether the extended Marshall mix design procedures can be reliably used to develop rut resistant asphalt mixes. The Marshall mixes were compared with Superior Performance Asphalt Pavements (Superpave) mix design procedure for secondary compaction and plastic deformation potential. Superpave design procedure was developed in the Strategic Highway Research Program (SHRP) to address drawbacks of the Marshall mix design procedure. Gabbro aggregate with neat (PG64-10) and styrene-butadiene-styrene (SBS) polymer modified bitumen (PG76-10) were used in Marshall mix designs. Various factors influencing the mix design procedures such as a drop in temperature and breaking of aggregates during compaction were studied. It was found that void at refusal density in the extended Marshall design procedure is not a reliable parameter in determining plastic deformation potential of asphalt mixes.