## 4 Factors Affecting the Successful Introduction of New-Age Nanotechnologies in Pavement Engineering  
### Toxicology, Health and Safety  
Concerns about toxicology, dangers to health and safety and environmental influences (e.g., leaching into the sub-strata and affecting the quality of ground water), need to be addressed from the onset with the use of any product (new or traditional). The fact that products have been in use for decades, do not exonerate them from any responsibility and liability towards health and safety aspects.  
Two chemical processes are usually applicable with the addition and use of nano-scale products during mixing with a carrying fluid and construction, i.e., a process of hydrolysis when mixed with the carrying fluid (e.g., mixing with water) and condensation (when the product attaches to the material during treatment or stabilisation). During any of these processes by-products can be formed. It must be ensured that any nano-scale product used, does not generate any by-product (liquid or gas) that may be toxic in any way. It is a fact, that the majority of organo-functional silanes are not suitable for general application and can be harmful to life-forms and to the environment. Silanes such as SiH\({}_{4}\) and silicon-hydrides (R-SiH\({}_{3}\)) and silicon-halides are \"toxic, volatile and generate hydrogen gas during hydrolysis\" [1], the effect of which is shown in Equation (1).  
\[\text{Hydrolysis: SiH}_{4}+4\text{H}_{2}\text{O}=\text{Si(OH)}_{4}+4\text{H}_{2} \tag{1}\]  
Other reactive groups involving fluorine (F) and chlorine (Cl) also form volatile and dangerous acids under hydrolysis, such as hydrofluoric and hydrochloric acids that are also detrimental to the various mineral groups and are not suitable to be used as stone consolidants [1]. Similarly, in combination with carbon (C), reactive groups containing chlorine (Cl) can produce chloroform (CHCl\({}_{3}\)) as a by-product during the hydrolysis (during mixing with water) or during the consolidation process (when attaching to the material), which is generally difficult to detect, but dangerous and even fatal when applied in confined areas or under conditions with low or no wind-speeds.  
In comparison, alkoxy-silanes (also referred to as organo-functional silanes) have low vapour pressures and do not form toxic gasses or acids during hydrolysis. It follows that the requirement of a health and safety toxicology report (Safety Data Sheet) should be a pre-requisite when considering the use of an appropriate nano-silane product for general application.  
The by-product formed during the hydrolysis process of the nano-silane when in contact with water, is of fundamental importance in the selection of an appropriate and applicable nano-silane to be used, in general engineering projects [6]. The most appropriate and designed alkoxy-silanes will form water as a by-product or at the worst, a non-corrosive alcohol [1].  
Many silane couplings, which are freely available commercially, will form siloxane bonds. However, of these, only a few known nano-silanes will have the \"correct balance of volatility and reactivity without being harmful to society\" or to the materials being treated [1]. The engineering fraternity need to ensure that applicable chemically based test procedures are in place to verify that no toxic by-products are generated during the construction process (or specify limitations of use when known dangerous by-products are generated (e.g., toxic fumes during the high temperature application of some traditionally used construction materials)). All products (including traditionally used construction products) need to be pre-evaluated and certificated on an equal basis, prior to approval for use in any construction process.