Impact of Superpave Mix Design Method on Rutting Behaviour of Flexible Pavements

Abstract

Effective communication is a key to national progress. Pakistan is located in a region where South-Asia converges with Central Asia and the Middle East. Blessed with extensive natural resources and rich agricultural land, it improves its economy particularly by exporting valuable items. In order to improve trade and economic activities and to materialize regional linkages with China, Afghanistan, Iran, Russia and other neighbouring Central Asian countries, the country is gearing up towards a large infrastructure network. Roads constitute a vital part of the infrastructure. In Pakistan most of the roads are constructed using flexible pavement concept, due to their comparatively low construction and maintenance cost. Pakistan has national highways with a length over 9555 Kilometers and motorways of 515 Kilometers. The drastic increase in traffic volume during the last few decades has resulted in premature pavement failures of almost the whole infrastructure of Pakistan. Premature rutting of flexible pavements is one of the major pavement distresses being faced by the country which is primarily due to uncontrolled axle load and high ambient temperatures. Rutting in asphaltic concrete depends on many factors, such as the composition of asphalt mixes, grading and quality of aggregates, type of binder, percentage of the bituminous binder, air void contents, degree of compaction, environmental conditions, load repetition, the substructure, and the bearing capacity of the subgrade. The objective of this research work was to compare the Superpave, Stone Mastic Asphalt (SMA) and Marshall methods of mix design of asphaltic concrete and to propose rut resisting asphalt mix suitable for local loading and environmental conditions. The mixes selected for the study were dense graded in case of Superpave and Marshall methods whereas gap graded for SMA. A comprehensive testing program was conducted on the samples prepared in the laboratory at the design asphalt contents and aggregate gradations. iiiPhysical properties of aggregates and asphalt were determined in the laboratory confirming to ASTM and AASHTO specifications. Mechanical Properties of Marshall, Superpave and Stone Mastic Asphalt (SMA) were evaluated by performing Indirect Tensile Modulus Test, Uniaxial Loading Strain Test (Creep Test), Dynamic Modulus Test and Wheel Tracking Test under prevailing load and environmental conditions of Pakistan in order to compare the performance of mixes. The study revealed that Superpave mixes performed better than Marshall and SMA mixes in terms of low induced permanent strains, high modulus of resilience, high dynamic modulus and better resistance against wheel rutting during wheel tracking test. Superpave technology can be adopted for the design of Hot Mix Asphalt (HMA) pavements in the country due to its superiority over the conventional mix design procedures. The guidelines for implementing Superpave mix design procedure in Pakistan have been proposed. In addition, a performance grading map has been proposed to be implemented in Pakistan by dividing it into seven zones according to the highest and lowest pavement temperatures. Keywords: Superpave, Rutting, Hot Mix Asphalt, Pavement