Application of coal fly ash in pavement subgrade stabilisation: A review.

Expansive clays are found in many countries worldwide, and they exhibit inherent volume change during the seasonal moisture variation causing cracks, heaves, and damages to the overlying pavements. Chemical stabilisation is one of the most used approaches to treat the expansive clay subgrades. Cement, Lime and Fly ash are the most commonly used stabilisers, in which fly is cheaper and a by-product obtained from the coal power plant. This paper reviews fly ash stabilisation on various clay types, including low plasticity clays, high plasticity clays, silty clays, organic clays, and peats. The review begins with the properties of fly ash, followed by the characteristics of fly ash stabilised subgrades. The micro-level mechanism, physical, mechanical, and hydraulic characteristics of stabilised pavements are presented graphically for the Class C, and F fly ashes. The micro-level studies reveal that the pozzolanic reaction is stronger than the cation exchange during the fly ash stabilisation. The unconfined compressive strength (UCS), California bearing ratio (CBR) and resilient modulus (Mr) increased with the fly ash addition and curing time for most soft soils except peat clays. Based on the mechanical and hydraulic characteristics, using 15% class C fly ash with 7 days of curing is recommended for optimum performance. Although few research studies confirm that the leachate limit of stabilised soil is within the acceptable limit, further studies are required to investigate the uptake of heavy metals and other certain carcinogenic contaminants. This study will provide key information for researchers and Engineers on the selection of fly ash stabilisation measures for expansive subgrades.

Recycling waste plastics in roads: A life-cycle assessment study using primary data.

The present study investigates - from an environmental perspective - the processes that lead to the conversion of waste plastics into recycled plastic pellets to be used either as an additive (wet method) or as a replacement of natural aggregate (dry method) in the production of asphalt mixes. Data from recycling facilities in Victoria, Australia, were collected and used as the basis for a comparative life cycle assessment (LCA) study. Analyses were conducted by considering several replacement ratios of virgin material by its recycled counterpart in the so-called wet and dry method. A case study considering the production of recycled-plastic asphalt to be applied in the construction of a typical surface layer of a road in Victoria was evaluated. In general, the results show that recycling plastics as a polymer for bitumen modification and as a synthetic aggregate replacement in asphalt mixes has the potential to be environmentally advantageous compared to their virgin counterpart (i.e. virgin polymers and natural quarry aggregates).