Abstract:
In parts of Namibia, Botswana and South Africa the only economically available road construction materials often contain excessive amounts of highly soluble salts such as NaCl (common table salt) and/or gypsum (CaSO4•2H2O) and fresh water for compaction is scarce. The Lüderitz and Haalenberg full-scale, long-term road experiments were therefore constructed in 1976 in the Namib Desert in Namibia in order to find ways of successfully using highly saline and gypseous materials as road pavement base course and of using seawater for the compaction of all layers. In this paper only those aspects concerning gypsum are presented. The experiments included a total of eight sections of G3 quality crushed stone bases with 2 – 20% added gypsum and two of G4 calcrete base with 5% (in comparison with the then permitted limit of 3,5%), in addition to their natural gypsum contents of 0,2 and 0,3% respectively, all under a 19 mm Cape seal surfacing. These experiments were monitored both during and soon after construction as well as for any long-term effects over a period of 36 years from 1976 until 2012. During this period the experiment only received two rejuvenation sprays and a minor amount of slurrying, edge patching, crack sealing and shoulder regravelling. For a 30-year design life and a capacity of at least 1,0M E80 under a 19 mm Cape seal, gypsum contents of up to 10% can be permitted in a G3 and up to at least 5% in a calcrete G4 base in this arid environment and probably in most of the southern African arid and semiarid zone.
