A study into the mechanical properties of foamed bituminous stablised materials

Abstract

Paper presented at the 21st Annual South African Transport Conference 15 - 18 July 2002 "Towards building capacity and accelerating delivery", CSIR International Convention Centre, Pretoria, South Africa.

Foamed bituminous materials have been used to a limited extent on a global scale before the early 1990’s when the lapse of the patent rights Mobil Oil Australia obtained in 1968 occurred. South Africa has also seen a number of projects involving foamed bituminous stabilisation being completed since 1994, with much success (Lewis, 1994). The design of foam mixes have not received as much attention as Hot Mix Asphalt (HMA) and the approaches used by the various users of the product have been secretive over the years due to the patent rights. To be more specific, over the past 10 years the HMA mix design approach has shifted from the Marshall mix design to methods that focus on investigating the fundamental material properties and relates test values to performance. Compaction of HMA has been the focus of many studies and the concept of using a standardised compaction effort for the design of different mixes have become obsolete. With the renaissance in the use of foam mixes, comes a need to establish sound compaction guidelines. Compaction methods used in the study were Marshall, Hugo, Kango, Superpave Gyratory compaction and a pedestrian roller. Marshall and Hugo compaction methods has have been used for a number of years in the design of HMA mixes in South Africa. The Kango hammer compaction method, involving the use of the Refusal Density equipment, was developed at the University of Nottingham (Brown et al, 1991). The Superpave Gyratory Compactor (SGC), one of the developments of the Strategic Highway Research Programme (SHRP), was used in this study (McGennis et al, 1995). Penetration grade bitumen used to produce foamed bitumen included 80/100 and 150/200 grades. Mechanical tests used in the project included the Indirect Tensile Strength Test (ITS), Indirect Tensile Test (ITT) and the Semi-Circular Bending (SCB) test.