Development of a new asphalt mix design manual for South Africa

Abstract

A need existed to update the South African design methods for asphalt mixes, particularly in the light of current developments in the country such as the revision of the South African Road Design System (SARDS), and the increasing demand for, and the use of products such as high modulus asphalt mixes with reclaimed asphalt and slags, warm mix, and cold mix as alternative mixes to conventional hot-mix asphalt. Generally, there is a worldwide shift from empirical-based asphalt mix design approach towards performance-related design approaches, due to advances in asphalt technology, increased volumes of heavy vehicles on roads, and there is also a demand for higher performance mixes, and a need to review the current criteria for asphalt layers in contract specifications. This paper presents the development of a new asphalt design manual. The paper presents key highlights such as (a) the performance grade binder selection methodology in which the binder is selected based on loading and environmental conditions, as a replacement of the traditional penetration grade binder selection method, (b) the move from aggregate grading bands (as per the current South African Committee of Transport Officials specifications) towards the use of control points to select the design aggregate grading, and (c) the three levels of asphalt mix designs proposed for the manual. The manual however, requires validation through additional laboratory testing before it can be used with confidence by industry.