Abstract
Lignin is the second-largest plant polymer on Earth after cellulose. About 98% of lignin produced in the papermaking and pulping industry is used for combustion heating or power generation. Less than 2% of lignin is used in more valuable fields, mainly in the formulation of dispersants, adhesives, and surfactants. Asphalt is one of the most important materials in pavement engineering. It is a dark brown complex mixture composed of hydrocarbons with different molecular weights and their non-metallic derivatives. Because the chemical structure of lignin is similar to that of asphalt, it is a carbon-based hydrocarbon material. More researchers studied the application of lignin in pavement engineering. In this paper, the structure, application, and extraction technology of lignin were summarized. This is a review article describing the different applications of lignin in pavement engineering and exploring the prospects of the application. There are three main types of pavement materials that can be used for lignin in pavement engineering, which are asphalt, asphalt mixture, and roadbed soil. In asphalt, lignin can be used as a modifier, extender, emulsifier, antioxidant, and coupling agent. In asphalt mixtures, lignin can be used as an additive. In road base soils, lignin can be used as a soil stabilizer. Furthermore, the article analyzed the application effects of lignin from the life cycle assessment. The conclusions suggest that lignin-modified asphalt exhibits more viscosity and hardness, and its high-temperature resistance and rutting resistance can be significantly improved compared with conventional asphalt. In addition, some lignin-modified asphalt binders exhibit reduced low-temperature crack resistance and fatigue resistance, which can be adjusted and selected according to the climate change in different regions. The performance of lignin as an asphalt mixture additive and asphalt extender has been proved to be feasible. Lignin can also produce good mechanical properties as well as environmental benefits as a soil stabilizer. In summary, lignin plays an important role in asphalt pavement and roadbed soil, and it is likely to be a development trend in the future due to its environmental friendliness and low cost. More research is needed to generalize the application of lignin in pavement engineering.
Highlights
The name lignin originated from the Latin word lignum, which means wood
About 98% of lignin produced by the paper and pulp industries is used for combustion heating or power generation, which is low in value, with less than 2% lignin used in more valuable areas, mainly in formulations of dispersants, binders, and surfactants
Lignin was modified by amination as a cationic emulsifier and added to asphalt binders to form asphalt emulsions stabilized by modified lignin, which were combined with reclaimed asphalt pavements as aggregates to create asphalt mixes with minimal environmental impact and high recycling efficiency (Yuliestyan et al, 2018)
Summary
The name lignin originated from the Latin word lignum, which means wood. Lignin is widely found in plants and is the secondlargest plant polymer on Earth after cellulose. Because the chemical structure of lignin is similar to that of asphalt and because lignin is a carbon-based hydrocarbon material, more and more people have begun to study the application of lignin in asphalt pavement in recent years. In the last 2 years, more and more studies have been conducted for lignin in asphalt pavements and road soil bases (Li et al, 2020a; Wu et al, 2021; Yu et al, 2021), and this paper provides a specific review of the application of lignin in them. From an economic point of view, the use of lignin in the asphalt binder industry can save costs, and several studies have shown that lignin can improve the performance of the asphalt pavement, making it an excellent material for prospective applications. The applications of lignin in pavement engineering are introduced and discussed from asphalt modifiers, asphalt fillers, asphalt coupling agents, soil stabilizers, life cycle assessment of lignin in the flexible pavement as well as the current and future development trend
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