Curing rates of emulsion-treated kalahari sand bases

Abstract

The curing rates of ten full-scale experimental road base sections of nonplastic, grey-white and red Kalahari sands treated with 2,5, 5,0 and 6,5% of SS 60 emulsion without added cement or inert filler were monitored by means of in-situ vane shear and Clegg Hammer tests at intervals of 1, 2, 4, 8 and 20 weeks. Rainfall at about ten days after compaction on the unprimed bases seriously weakened the grey sand ETB sections to less than that of the untreated red sand control section but had less effect on the red sand sections. After about 8 weeks only the red sand sections had achieved their design strength of 200 kPa at 40ºC. The sections were primed after 14 weeks and, with shear strengths of 230 – 475 kPa in comparison with the 440 kPa of the untreated nonplastic red sand, all had easily exceeded their design strength when surfaced after 20 weeks at FFCs of about half their OFCs. However, Clegg Hammer CBRs uncorrected to 40ºC were mostly only 48-74, with only the 2,5 and 6,5% red sand sections − as well as the untreated, red sand − exceeding an in-situ CBR of 80. Clegg Hammer impact values correlated well with vane shear strength and may be a more convenient alternative to the vane shear test. The red sand ETBs were less temperature-sensitive, less affected by rain, and cured more rapidly to higher early strengths than the grey sand ETBs, probably due to a positive charge imparted by the sesquioxides accelerating the breaking of the emulsion, but did not all develop higher strengths when surfaced after nearly five months. With anionic emulsion the red sands are to be preferred to the grey, for which a cationic emulsion should be more suitable. Specifications for an untreated red sand base course in terms of vane shear strength or Clegg Hammer tests are derived.