A Comparison of the Marshall and Superpave Design Procedure for Materials Sourced in India

Abstract

Developing countries are striving for the development of infrastructure facilities including transportation systems. India has a national highway with a length over 52,000 km. A further 14,000 km length of express highway is currently being built under the golden quadrangle and North–South and East–West corridor projects. These projects have large scope for adopting superpave technology.

The strategic highway research program (SHRP) conducted a $ 50 million research effort from 1987 to 1993 to develop a new concept for the design of bituminous mixes referred to as superior performing asphalt pavements (superpave). Superpave mixes have been widely used by the developed countries for the last few years but the developing countries are still working with the conventional mixes i.e. marshall mixes. Flexible pavements, with bituminous surfacing as a wearing course, are widely used in India. The objective of this study was to compare the design of asphaltic concrete by the superpave and marshall methods of mix design. A detailed laboratory study was carried out using aggregate from the Delhi region and bitumen from the Mathura refinery. From the analysis of design of asphaltic concrete, it was observed that superpave mixes fulfill all the criteria for easy and good construction at lesser binder content than the marshall mixes. Apart from superpave mix design, the effect of angle of gyration, number of gyrations on mix properties like density, stability, indirect tensile strength were also determined. Results revealed that percentage theoretical maximum density increases with the increase in number of gyrations. At any level of gyration, theoretical maximum density percentage increases with increase in gyratory angle. Further, it was observed that indirect tensile strength decreases with increase in angle of gyrations.

Comparing both the design methods, it was observed that marshall compactor is unable to answer the rutting resistance of the designed mixture. The marshall compaction effort in the field laboratory corresponded to an air void content of slightly less than six percent, and the mixture appeared to stabilize under traffic at an air void content between three and four percent. In contrast, superpave gyratory compactor is capable of achieving air void contents much lower than achieved by mechanical marshall hammer compaction. This prevents additional compaction under traffic, which could result in rutting in the wheel paths. Hence, marshall mix design should be replaced by superpave mix design for Indian national highways/express highways, which compact the specimens in the same manner as compacted under actual pavement climate and loading conditions.

Keywords:

• Gyratory compactor
• Rutting resistance
• Golden quadrangle
• National highways
• Mathura refinery