Review of current and future bio-based stabilisation products (enzymatic and polymeric) for road construction materials

Abstract

In situ soil modification is required in order to improve the primary engineering properties of the material to meet a road construction standard. Bio-stabilised soil is an environmentally friendly, cost-effective alternative to imported granular fills, concrete, costly hauling of materials or export to a landfill. In-service soil performance and required maintenance is highly dependent on methods of stabilisation, ranging from expensive mechanical stabilisation to chemical processes. As such, many alternative materials originating from bio-based sources are being explored as potential stabilising additives to improve weak subgrade soils (i.e., dispersive, erodible and collapsible soil, and soft or expansive clays). Some key solutions include the use of bio-derived enzymes, microbes, and polymeric additives to avert road failure caused by water penetration and/or erosion. The role of microbial substrate specialisation has been largely unexplored, since the level of research done on alternative stabilisers consists mostly of small ad hoc studies. In addition, research has focused on a reduction in permeability and an increase in compressive strength using enzymes and polymers, however, the complexity of these products and their implementation for a wide range of soil types and structural applications remain limited. Currently there is a need for more supporting research methodologies and systematic approaches on the implementation of bio-based materials for infrastructure development. This also includes the simplification of bio-based products for potential construction applications. This review provides (a) an overview of soil stabilisation techniques, (b) the primary challenges that lay ahead for future research in bio-based stabilisation products application in the road sector and (c) innovations to address the challenges of using modernised techniques in the road construction industry (i.e., weak subgrade and the required maintenance thereof, as well as the development of potential bio-based additives for unpaved road construction application).