## 3 Traditional Use of Nanotechnology Products in Road Pavement Engineering
### Chemistry of Organofunctional Nano-Silanes for Application in Pavement Engineering
The functionality of the silane R-Si-X molecule in terms of an aggregate adhesive mainly refers to the ability of the (X) reactive group to be removed from the molecule when in contact with water (to effectively be chemically detached by water) and replaced by a hydroxyl (OH) group, during a process referred to as hydrolysis [4]. Hydrolysis: Si-X + H2O = Si-OH + XH  
The one product of hydrolysis is the Si-OH binding referred to as silanol [4]. Silanols are now able to react with each other to form siloxane bonds in a condensation reaction when in contact with an inorganic material (e.g., granular material such as rock/gravel/soil) [4], covering the total area of each particle in the granular material. It should be noted that the by-product during condensation should preferably be water (H2O), as shown in the example (not all available nano-silane products produce water as a by-product, at worst a non-toxic alcohol should be allowed to form as a by-product during condensation--refer toxicology requirements [7]). where:  
\[\text{Condensation: Si-OH + OH-Si = Si-O-Si + H2O} \tag{6}\]  
Of importance to the field of pavement engineering is that the organic (R) (organofunctional) group attached to the silicon by means of a direct Si-C bond is not affected by hydrolysis and will remain stable (non-reactive) also during condensation. It follows that in the case of CH3-Si-(OCH3)3 (methyl-trimethoxy-silane), the methyl group (CH3) directly attached to the silicon atom will remain stable throughout the process of hydrolysis and condensation, while the hydrogens in the methoxy ((OCH3)3) groups will react with water. These effects of hydrolysis and condensation are demonstrated as follows [4]:  
\[\text{Hydrolysis: CH}_{3}\text{-Si-(OCH3)}_{3}+3\text{H2O}=\text{CH}_{3}\text{-Si-(OH)}_{3}+3 \text{CH}_{3}\text{-OH} \tag{7}\]  
\[\text{Condensation:} \tag{8}\]  
In order to be effective as a consolidant, the silane-compounds must be able to form three-dimensional networks and hence, must have at least three reactive groups. The pavement engineering implications (macro-effect) of the above nano-silane formulations are demonstrated in Figure 5, which should be considered together with Figure 4 and the similarities with the emulsifying agent shown in Figures 1 and 2. The effective result shown in Figure 5 is that the surface of each particle comprising the granular material (rock/aggregate /soil) will chemically be changed from a hydrophilic (water-loving) to a hydrophobic (water-repellent) state that attracts an organic material (such as oil/bitumen or an equivalent material compatible polymer). Consequently, the  
Figure 5: Simplified demonstration of the chemical interaction between a stabilising agent, organofunctional nano-silane modification and the mineralogy of the rock/stone/soil granular material sub-strata. water molecules that are naturally attracted to exposed surfaces of granular materials (stone/aggregate/soil) due to the presence of broken chemical bonds as discussed and demonstrated in Figure 4, will now actively be repelled together with the water that is the by-product formed during the condensation phase (as per the example shown in Figure 5). Figure 5 represents a most basic schematic explanation of the practical use of nano-silane science in pavement engineering. The changing and matching of reactive and non-reactive bonds to the silicon element can result in literary numerous different nano-products with different characteristics, which could match the numerous minerals available in naturally available materials such as stone, gravel or soils.