Application of lignin as bioasphalt in pavement engineering: a review on production, characterisation, and performance evaluation

Reducing greenhouse gas emissions is one of the United Nations’ Sustainable Development Programme’s agendas, and net-zero emissions will be the ultimate objective by 2050. In this context, the use of biobased fuels, chemicals, and materials is being promoted globally, as biobased products emit fewer emissions. Lignin is a potent, abundantly available biobased material derived from plants. It is the by-product of the pulp and paper industry and the second-generation ethanol production process. Of lignin, only 2% is valorised to produce biobased products, and the rest, 98%, is burnt to produce heat and power for local use. Therefore, lignin is being explored as an alternative to bioasphalt in pavement engineering. Bioasphalt is a black, viscous material obtained from crude petroleum, which consequently leads to massive emissions. In order to achieve net-zero emissions, the International Renewable Energy Agency (IRENA) ‘s goal of stopping fossil fuel use by 2050. Therefore, bitumen will not be available by the year 2050. The finite availability of crude petroleum is also a cause for concern. It is reported that 85% of the bitumen consumed globally is used in pavement engineering, estimated at 100 million tons per year. Numerous studies show that bio-asphalt prepared by mixing lignin can achieve performance comparable to conventional asphalt in terms of fatigue, rutting resistance, and moisture susceptibility when properly formulated. In addition, its compatibility with warm mix asphalt results in lower production temperatures, lowering energy consumption and emissions during construction. Therefore, this review summarises the literature on the use of lignin as an alternative to bitumen in asphalt production, characterisation, and performance evaluation.