Abstract:
Calcretes are probably the most widely used road construction materials in southern
Africa, rank second after dolerites in relative importance in South Africa and are often the
only available materials in the vast area covered by Kalahari sands. After a back-analysis
of some old calcrete-based roads in the Western and Eastern Cape in the 1960s indicated
that substantial relaxations in plasticity, grading and even CBR might be possible,
purpose-built LTPP experimental sections were constructed in Botswana, Namibia and
South Africa in order to test this hypothesis. The performance of one of these – the
Biesiesvlei plastic calcrete base experiment constructed in 1976 on the now N14-11 in the
North West Province – until failure after 0,5 MESA in 30 years is described. Three simple
specifications for a similar calcrete base for a Category C road in dry and borderline
moderate macroclimatic regions for structural capacities of 0,3; 0,5 and 0,8 MESA were
derived empirically from the comprehensive test and performance data collected. These
all require a GM of 1,7 ‒ 2,5 and, depending on capacity, a maximum PI of 16 ‒ 14, a
maximum LSM of 320 ‒ 260, and a minimum 98% soaked CBR of 40 ‒ 60.
