The biesiesvlei long-term plastic calcrete base experiment: performance over 30 years until failure

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.