The orapa emulsion-treated kalahari sand experiment: performance over 30 years and derived material and pavement designs

Abstract

The purpose of this experiment on the Serowe-Orapa road in Botswana constructed in 1989 was to evaluate the performance of both grey and red fine Kalahari sands treated with SS60 emulsion both in the upper half only and the full 150 mm of the base. After 19 years of regular performance monitoring and 0,3 MESA, ten test and three control sections were still in a good to very good condition and all were still in a satisfactory condition after 30 years and a projected 0,5 MESA. The red sand sections performed better than the grey and only the 2,5% emulsion half-depth grey sand section failed. Maintenance applied over the first 20 years was a fog spray, two reseals and patching of edge breaks, mole tunnel depressions and, on two grey sand sections, base course shear failures. CBR and UCS empirical laboratory design guidelines for SS60 ETBs for both grey and red sands with 2,5 – 6,5% emulsion as well as the requirements for the raw sand and the whole pavement, are presented. The most economical designs are red sands with 2,5% emulsion in the upper base only for up to a projected 0,8 MESA and 2,5% in the whole base for up to 1,0 MESA for a Botswana Category II or a South African Category C road.