The use of seawater in road construction : part 3 – a quick guide to an accelerated construction method

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.