The purpose of this experiment on the Serowe-Orapa road in Botswana constructed in 1989 was to evaluate the performance of untreated, Kalahari fine red sand against similar sand treated with 2,5% bituminous emulsion and ferricrete gravel control sections. After 19 years, 0,3 MESA, two reseals and no patching the test and two control sections were still in a good to very good condition. DCP testing indicated that the sand base course had an in-situ CBR of about 160 and the pavement a total capacity in excess of 1,0 MISA and at least 0,5 MESA by a conservative extrapolation of rut depths, in comparison with about 0,8 MESA of the ETB. The high in-situ strength of the base was due to suction-induced apparent cohesion due to the low moisture contents. A specification derived for such an untreated red sand base course on similar red sand lower layers with untreated red sand sealed shoulders and a double seal on the carriageway for up to 0,5 MESA for a South African Category C, 0,6 for a Category D and 0,8 MESA for a Botswana Category II road over 20-30 years includes the following: GM 1,10-1,20; Passing 425 μm 75-85%; PI on P425 μm NP, on P075 μm 2-40; min. soaked MAASHO CBR 60; min. CBD-extractable Fe 0,3% or 1,5% Fe203 by XRF analysis. Whilst extra care is needed in construction and surfacing, such a pavement has tremendous potential for economical, low-volume, sealed roads in the vast area covered by Kalahari sands in which rock and conventional gravels are scarce.
Papers presented virtually at the 39th International Southern African Transport Conference on 05 -07 July 2021