## 1 Introduction  
In any country the efficiency of ground transportation is highly dependent on the quality of their network of roads. In South Africa (SA) the national road network contains kilometers of unpaved (i.e., gravel) roads, as well as unclaimed roads or rural roads [1]. South Africa has more than 500,000 km of unpaved roads; however, these roads generally do not provide all-weather pass-ability, they are of poor riding quality, impassable in wet weather, and produce excessive dust in the dry weather. Yet, these roads are critical in providing access to rural and poorer areas, where the majority of the population reside. These roads are an important factor in supporting a rural-based economy of the country. Even though it is important in developing countries to uplift the socioeconomic conditions of communities, the prioritisation and improvement of these roads throughout the world are typically overlooked. This is seen with the issue of rural roads in particular, due to increasing environmental legislation, high-cost for upgrading and maintenance, and limited resources [2]. The practice of gravel replacement to maintain these roads is unsustainable. The solution is either to treat the material in situ with chemical additives or to upgrade to a surfaced road. The quality of typical soils for unpaved roads can be improved with traditional chemical additives such as, cement, lime, and bitumen. However, even with cement's numerous applications and low cost, it has been determined that the over-dependence and overuse has led to several global environmental concerns such as, high CO\({}_{2}\) emissions, increase in pH (12-14), urban water runoff, heat islands, and prevention of vegetation growth. Furthermore, the use of cement itself does not always solve the issue of environmental compatibility, as soil-cement may not be compatible with weak dispersive clay for slope stabilisation [3]. Worldwide awareness enforces the use of greener technologies, specifically targeted at de-carbonising the global economy. With significant statistics supporting a bioeconomy there has been a strong drive from agencies such as, the South African National Roads Agency SOC Ltd. (SANRAL) to investigate alternative 'green' construction materials for road improvement and maintenance. Previous field investigation studies have shown the potential use of electrochemical-based non-traditional stabilisers (defined as chemical-based formulations or modified traditional stabilisers) to improve unpaved road performance [4]. However, in that study, it was difficult to conclude whether the enzyme based additives or the sulfonated oil showed significant improvement, due to variability in terms of the density of gravel, in situ strength based on dynamic cone penetration (DCP) results and California bearing ratio (CBR) testing, and the lack of knowledge on associated testing procedures for non-traditional additives (i.e., considering time, moisture regime, and traffic load intensity as factors). Non-traditional stabilisers are known to have mixed results and are material dependent. Good wearing course on unpaved or earthen roads should have the ability to resist the abrasive action of traffic and erosion by water. In this case, it is important to evaluate the requirements of non-traditional additives and properties of the wearing course materials for unpaved road applications in relation to their micro- and macro-structural performance. Soil compatibility is, thus, a factor that needs consideration, as the effectiveness of the stabiliser/additive will vary with the soil type. The traditional choice and type of stabilisation depends on whether the soil has a high or low plasticity index (PI). This results in different processes and mechanism of stabilisation. Numerous proprietary chemical products such as Terrazzyme and Permazyme are commonly investigated bio-enzyme based products. They have been found to give mixed results and confirm the findings of previous studies that enzyme-based products are soil material dependent.