Investigation into the Source of Self-Hardening of Calcrete

Calcrete has been used as road construction material in Botswana for a very long time even though it is classified as marginal or sub-standard material (AFCAP/MOZ/091, 2012). Some calcrete has proved to perform exceptionally well past the road design life and this has been attributed to a property termed self-stabilisation. However, the science behind self-stabilization of some calcrete deposit is not yet fully understood. Accordingly, this paper presents preliminary results of an investigation undertaken to determine the sources of self-stabilization of calcrete deposits. Calcrete samples were collected from borrow pits along Francistown – Nata road. The samples were subjected to a series of laboratory tests including soil indicator tests, standard California Bearing Ratio, California Bearing Ratio following wetting and drying cycles, Compaction, Petrification Degree, X-ray fluorescence and X-Ray Diffraction for types of minerals present. Preliminary results indicate that calcrete would only have potential for self-stabilisation if it can absorb an amount of water equal to its volume of voids. This allows the solution and deposition of orthoclase minerals to take place. It is concluded that self stabilisation depicted by some calcrete is attributed to their unique mineralogical composition of orthoclase.