Some Considerations in Bituminous Mix Design Awaiting Implementation in Highway Construction

Bituminous mix design is a delicate balancing act between the proportions of aggregate sizes and bitumen content. For a given aggregate gradation, the optimum bitumen content is estimated by satisfying a number of mix design parameters recommended in the specifications. In this paper, some of new considerations related to the bituminous mix design are discussed. Bituminous mix design, with these considerations included, are expected to yield better performance if implemented in highway construction. 1.0 Introduction Construction of highway involves huge outlay of investment. A precise design may save considerable amount of investment, as well, a reliable performance of the in-service highway can be achieved. Two things are of major considerations in this regard – pavement design and the mix design. The present paper emphasizes some of the new considerations involved in the concept of mix design. Though there are a few equipment used for estimation of stability of the bituminous mixes in the laboratory, the Marshall test is the most popular one, possibly due to its simplicity and low cost. The Superpave recommendations [1,2] have rationalized the concepts of bituminous mix design to a great extent, however, this involves evaluation of mix properties through a number of costly equipment. The discussion in this paper has been kept confined to the Marshall and fatigue testing only. Discussion has been covered in two parts in this paper. The first part contains some of the new considerations in the bituminous mix design, and the second part discusses about the concepts awaiting field implementation. 2.0 Some New Considerations in Mix Design Concept The mix volumetrics, reliability of bituminous mix design and the incorporation of fatigue considerations in bituminous mix design are the three aspects covered in this section.