1. Professor, Univ. of Pretoria, Lynnwood Rd., Hatfield, Pretoria 0002, South Africa (corresponding author).
2. Graduate Engineer, Aurecon Centre, 1 Century City Dr., Waterford Precinct, Century City, Cape Town 7441, South Africa.
3. Office Manager and Specialist: Pavement and Materials, Ndodana Consulting Engineers (NCE), Plot 125, Section 2, C/O South and Von Willich, Lyttelton, Johannesburg 0002, South Africa.