Abstract:
The usual South African requirement for the maximum soluble salt content of the base and
subbase of a road to be covered with a bituminous surfacing as determined by the paste
electrolytic conductivity (EC) test of 0,15 S/m is a conservative limit intended for normal
use without requiring any special design or construction precautions. Compaction of most
pavement materials with an inherently low EC of less than about 0,1 S/m with seawater or
other comparable chloride-sulphate water with a salinity of about 3,5% will raise the EC to
about 0,5 S/m, which exceeds even the maximum of 0,40 S/m usually specified for
selected subgrade layers. A design and accelerated construction method was therefore
developed from experience and research in order to enable the use of both inherently
saline materials and waters with a salinity up to about that of seawater for compaction with
little risk of salt damage. This essentially involves covering each layer with the next as
soon as practicable in order to minimise upward migration during construction and then
priming and sealing the base as soon as practicable with an impermeable surfacing in
order to keep the salt safely in solution. The maximum target delays between the
pavement layers derived from local experience and LTPP experiments together with
additional precautions are summarised, together with comments on evaluating water for
road compaction.
