A sustainable soil stabilisation technique using marble sludge for road and railway construction

The utilisation of soils in the field of civil engineering represents a foundational aspect of construction, as soils provide suitable materials for the construction of substantial earthworks, such as embankments, landfill barriers, and earth dams. In the field of road and railway engineering, soils are extensively utilised in the formation of subgrades and embankment bodies. Conventional construction practices frequently involve the utilisation of higher-quality borrow soils obtained from quarries. Nevertheless, contemporary construction is placing greater emphasis on the adoption of sustainable solutions. The extraction of high-quality construction materials is associated with the depletion of non-renewable natural resources. Furthermore, the growing demand for resilient and efficient transport infrastructure in construction and maintenance has intensified quarrying activities, leading to the progressive exhaustion of virgin resources. Concurrently, infrastructure development generates substantial amounts of excavated soils that are frequently deemed unsuitable for direct reuse and are consequently designated as waste. The management and disposal of these materials pose significant organisational, economic and environmental challenges, principally due to the transportation requirements and the use of land for landfill sites. The increasing focus on sustainable development has served to underscore the significance of the implementation of strategies that can be considered sustainable. Governments, institutions and research communities worldwide are developing strategies to minimise the environmental impact of human activities. In this context, the construction sector is of particular significance, given its consumption of up to 40% of all raw materials, its extraction of natural aggregates estimated at approximately 50 billion tonnes per year, and its responsibility for approximately 50% of global greenhouse gas emissions. Earthmoving operations associated with the construction of road and railway infrastructures involve substantial costs, high consumption of natural resources, and significant CO2 emissions. In the context of large-scale earthworks, such as embankments or subgrades, construction sites require substantial quantities of high-quality geomaterials. The transportation of large volumes from quarries significantly increases both project costs and additional emissions, which are produced as a result of the transportation of large volumes of materials. Initiatives like the European Green Deal placed sustainability as a pivotal principle in social development, promoting the transition to climate neutrality and encouraging the adoption of circular economy principles that reduce CO2 emissions. From the perspective of the circular economy, there is an increasing emphasis on the reuse of excavated soils, which would otherwise be disposed of as waste. In the context of earthworks, soil stabilisation is frequently employed as a technique to enhance soil properties and facilitate the direct reuse of excavated materials directly on construction sites. Chemical stabilisation is commonly achieved through the addition of binders such as lime or cement, which enhance the mechanical behaviour of soils and allow them to meet construction requirements. In particular, soils with a high clay content, which are typically characterised by significant swelling and shrinkage behaviour when exposed to water content variations, can be effectively treated through lime stabilisation. This represents an eco-friendly technique capable of improving the hydromechanical behaviour of fine-grained soils while simultaneously minimising the consumption of non-renewable resources and reducing the need for landfill disposal. Despite the clear advantages of conventional stabilisation techniques, the production of traditional binders such as lime and cement is associated with significant CO₂ emissions. This could compromise the environmental benefits of soil stabilisation. Consequently, recent research has increasingly focused on the identification of alternative binders capable of reducing the environmental impact of stabilisation processes while maintaining or improving engineering performance. The utilisation of locally available industrial by-products and waste materials has attracted significant interest as a potential strategy for enhancing the sustainability of soil stabilisation practices. The aim of this work is to investigate the reuse of marble sludge from the Sicilian marble industry as a binder capable of reproducing the stabilising effect of industrial quicklime. With a micro and macro characterisation of proposed soil stabilised mixtures this work poses a significant challenge to the re-utilisation of this unsewn by-product within the paradigm framework of a locally circular economy.