## 3 Pavement Design Process Based on Scientific Principles
### Scientifically Based Material Properties of Naturally Available Materials
#### 3.2.2 Primary Minerals Defining the Type of Stone
Figure 4 [32], for example, gives the lithological properties of the surface geology of the African continent, clearly showing that large areas of the surface geology of the continent, especially around southern Africa, the Horn of Africa and norther Africa contain Carbonate materials not suitable for NME stabilisation using a conventional nano-silane modification. The surface material distribution is not unique to the African continent, as shown by the soil distribution map of Africa in a global context in Figure 5 [32]. Figure 3: Silicon content variation versus Carbon-dioxide content found in some typical and commonly known naturally available materials. The crust of the Earth is anything from \(\pm 5\) km (oceanic) to \(\pm 70\) km (continental high mountains) thick, and only the surfacing is subjected to the harsh climatic conditions conducive to chemical weathering and conditions resulting in sedimentary materials. Over and above the obvious, such as the non-Silicate materials mentioned, naturally available materials in climatic regions conducive to chemical weathering (Table 1) could have considerably reduced percentages of the Silicate materials due to a process of dilution or \"washing out\" in high rainfall areas, i.e., especially regions near and around the tropics. The distinction between Silicate and non-Silicate and Silicon-poor materials is of importance as it forms the basis for the design and selection of an applicable effective NME stabilising agent. High percentages of other minerals such as Calcium Carbonates (CaCO\({}_{3}\)) in the material to be stabilised will require a different modification in terms of a Hydroxy Conversion Treatment (HCT) [3; 11] in order to provide high strength \"permanent\" bonding of the stabilising agent with the available elements in the material to meet engineering requirements. Figure 4: Ref. [32]: Example of the variation in surface geology of the continent of Africa showing large parts of the content that a general assumption of the presence of Silicate materials could have dire design and construction consequences. It should be noted that even Feldspars (which compromises about 60 per cent of the crust of the Earth (Figure 2)) may, in terms of the broad mineral classification of Alkali and Plagioclase (Figure 6 [33]), vary considerably depending on the basic elements present in the material. Plagioclase could contain high concentrations of free elements (elements with broken bonds available for effective bonding with a stabilising agent) such as Calcium (Ca) that will influence the classification and the selection of a material-compatible modification of an appropriate stabilising agent. Table 3 [33] gives an indication of the variation possible within the Plagioclase Feldspar group of materials, as indicated in Figure 6. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Mineral** & **\% Albite** & **\% Anorthite** \\  & **(Na(AlSi\({}_{3}\)O\({}_{8}\)))** & **(Ca(Al\({}_{2}\)Si\({}_{2}\)O\({}_{8}\))** \\ \hline \hline
**Albite** & 100–90\% Ab & 0–10\% An \\ \hline \hline
**Oligoclase** & 90–70\% Ab & 10–30\% An \\ \hline
**Andesine** & 70–50\% Ab & 30–50\% An \\ \hline
**Labradorie** & 50–30\% Ab & 50–70\% An \\ \hline
**Bytownite** & 30–10\% Ab & 70–90\% An \\ \hline
**Anorthite** & 10–0\% Ab & 90–100\% An \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Variation in minerals within the Plagioclase Feldspar group of materials as shown in Figure 6 [33]. Figure 5: Ref. [32]: Distribution of surface material characteristics (soils) of the African continent in the global context with specific emphasis on the distribution of non-Silicate materials, such a Calcisols and Camisoles. The identification of the primary minerals comprising the materials could be pivotal to determine the success of any nano-modification of a stabilising agent. At a bare minimum, the percentages of the main elements, as identified in Table 2, must be determined.