Review on Applications of Lignin in Pavement Engineering: A Recent Survey

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.

Investigation of flexible pavement maintenance patching factors using a finite element model

Patching of flexible pavements is one of the most important functions of pavement maintenance. Although finite element modeling has become commonplace in the world of pavement engineering, modeling has not yet been significantly leveraged for maintenance applications which improve safety, ride quality, and pavement service life. The objective of this study was to model viscoelastic properties of pavement and patching materials to determine the effect of various repair factors on pavement performance using the finite element method. Specifically, surface permanent deformation, local shear stress concentration, and horizontal strain distribution were investigated. Two types of models were simulated; the first model applied static loading to a surface layer fixed on a plate and the second model applied cyclic traffic loading to a two-layered flexible pavement system. The results demonstrate the importance of patching using a semi-permanent method. The results also demonstrated the accumulated effect of repeated loading using a time-dependent material response. Results also indicated that a larger patching area resulted in less influence of the shape of the area, while a circular area proved superior to a conventional rectangular patch for sizes near the tire footprint and smaller than it. Different responses were observed depending on the type of patching material modeled, demonstrating the effect of material choice in maintenance applications. Finally, mesh optimization was performed to ensure appropriate mesh sizes are used in future studies to accurately represent the pavement layers and patches.

Application of Steel Fibre to Improve the Self-Healing Mechanism of Bituminous Mixtures: A Review

The self-healing mechanism of bituminous mixtures was demonstrated through several studies and was recognised for developing sustainable road pavement. This paper presents a comprehensive summary of various studies related to steel fibre as a self-healing mechanism of bituminous materials. Based on the extensive literature, it was found that steel fibre was likely to be used in the asphalt industry due to several benefits. First, the idea of using steel fibre in pavement engineering materials gives great attention to their utilisation in asphalt. It helps increase the self-healing mechanism and contribute to reducing the problem related to potholes, ravelling, slipping during raining while driving and many more. Second, this study identifies the gap of research for future research in pavement engineering. Finally, some proposals were made for the possible construction of self-healing asphalt.

Gene-editable materials for future transportation infrastructure: a review for polyurethane-based pavement

With the rapid development of society and industry, novel technologies and materials related to pavement engineering are constantly emerging. However, with the continuous improvement of people’s demands, pavement engineering also faces more and more enormous challenges that the pavement materials must have excellent engineering properties and environmental benefits. Meanwhile, the intelligence is the mainstream development direction of modern society, and the development trend of future transportation infrastructure. Materials Genome Initiative, a program for the development of new materials that materials design is conducted by up-front simulations and predictions, followed by key validation experiments, the rapid development of science and technology and AI toolset (big data and machine learning) provide new opportunities and strong technical supports for pavement materials development that shorten the development-application cycle of new material, reduce cost and promote the application of new carriers such as intelligent sensing components in transportation engineering, to achieve the intelligence of transportation engineering. However, traditional pavement materials possess several unavoidable shortcomings, indicating that it is exceedingly difficult for them to meet the above requirements for future pavement materials. Therefore, the development of future new pavement materials, which can be designed on-demand as well as possessing enough mechanical properties, high durability, practical functionality, and high environmental protection, is urgent. In recent years, as a “designable” polymer material with various excellent engineering performances, polyurethane (PU) has been widely applied in pavement practices by changing the chemical structures of raw materials and their mix proportions, for instance pavement repairing material, permeable pavement material, tunnel paving material and bridge deck paving materials, etc. Although PU material has been widely applied in practices, a systematically summarization is still quite necessary for further understanding the working mechanism of PU materials and optimization it’s engineering applications. To fill the gap, this article puts forward the special requirements for future transportation infrastructure materials, and introduces the basic properties and working mechanism of PU materials in order to make up for the defects of conventional road materials. Based on this, this article also summarizes the engineering performances and environmental benefits of applying PU as the binder for different road infrastructure materials in recent years. Considering the gene-editable nature of polyurethane, further research of the on-demand design principles of PU pavement materials is recommended. The establishment of raw material gene database, material terminal performance database and their structure-activity relationship are highlighted. The current research is essential to the practice guidance and further optimization of the PU materials for road infrastructures, which in line with the future Carbon neutral policy.

Engineering Properties of New-Age (Nano) Modified Emulsion (NME) Stabilised Naturally Available Granular Road Pavement Materials Explained Using Basic Chemistry

Nanoscale organofunctional silanes have been developed, tested and successfully applied to protect stone buildings in Europe against climatic effects since the 1860s. The same nanotechnologies can also be used in pavement engineering to create strong chemical bonds between a stabilising agent and granular material. The attachment of the organofunctional silane to a material also changes the surface of the material to become hydrophobic, thereby considerably reducing future chemical weathering. These properties allow naturally available materials to be used in any pavement layer at a low risk. In the built environment, scientists soon determined that the successful use of an organo-silane depends on the type and condition of the stone to be treated. The same principles apply to the implementation of applicable nanotechnologies in pavement engineering. Understanding the basic chemistry, determining the properties of the stabilising agent and the organofunctional modifying agent and the chemical interaction with the primary and secondary minerals of the material are essential for the successful application of these technologies in pavement engineering. This paper explains some basic chemistry, which fundamentally influences engineering outputs that can be achieved using New-age (Nano) Modified Emulsions (NME) stabilising agents with naturally available granular materials in all road pavement layers below the surfacing.

Performance and Fracture Analysis of Composite Interfaces for Semi-Flexible Pavement

Semi-flexible pavement is widely used in pavement engineering due to its excellent rutting resistance; however, it mainly fails due to cracking. Therefore, it is important to understand the properties of the aggregate–mortar–asphalt interfacial transition zone, to better understand the cracking mechanism of the semi-flexible pavement. In this work, we used pull-off tests and digital image analysis technology to compare and analyze the interfacial tensile strength and granite–bitumen–mortar interactions in three types of asphalt (70# matrix asphalt, PG76-22 modified asphalt and S-HV modified asphalt) at different curing ages. The analysis results showed that, for the three different bitumen materials, with settled mortar, the peak interfacial tensile strength values all occurred at approximately 14 d of curing. In addition, the order of the tensile strength followed the order of asphalt penetration degree; the order of the interfacial water damage resistance from weak to strong was 70# asphalt cementation specimen, PG76-22 modified asphalt cementation specimen, and S-HV modified asphalt cementation specimen. The results of this analysis highlight the original contributions of the optimum curing time for the composite interface of semi-flexible pavement materials prepared with different asphalts to reach optimum crack resistance.

Influence of Texture on Drainability, Splash and Spray in Flexible Pavements

Although the splash and spray phenomenon produced by heavy trucks on road pavements is not a significant issue in relation to traffic safety, it may cause considerable inconveniences for those driving cars or motorbikes. This paper addresses the issue of pavement engineering with regard to surface characteristics; particularly pavement texture and its influence on water mobilization and projection in conditions of wet weather and heavy traffic. Considering the theoretical concept of pavement macrotexture, the analysis starts with the hypothesis concerning a relationship between Mean Profile Depth (MPD) and water splashed during rain. In order to focus on the impact of texture on splash and spray, a field experiment was carried out to test the hypothesis using 5 test tracks on a range of different pavement textures. The experiment was performed using a Traffic Speed Drain Meter (TSDM), which is a new drainability survey device presented to PIARC for approval. This equipment employs the laser and image technology and allows one to simultaneously obtain MPD and water splash data. The results of drainability and MPD were compared for each test track. Having analysed the pavements with different MPD ranges in the experiment, it has been concluded that MPD and water splashed apparently have an inversely proportional relationship. In addition, the TSDM proved to be a suitable equipment (repeatability) at an affordable cost (high performance of data collection). Finally, it has been concluded that there is a way to reduce splash and spray adjusting the infrastructure rather trying to solve the issue modifying vehicle moving modes. Therefore, if the issue is properly addressed by civil engineers and road managers, road safety in the areas of heavy rain may be improved at an affordable cost. The experiment presented here is considered a starting point opening the path for further research.