Search

• History of DEM and the development of DEM in China are described. • Generation of aggregates based on DEM is divided into modeling and filling. • Application of DEM in material property and mixture performance is reviewed. • Future development directions of aggregate simulation based on DEM are proposed. As one of the primary materials in asphalt mixtures, aggregates' complex morphologies and size directly affect the service performances of pavement, such as the structure stability and force transmission path. Discrete element method (DEM) can be effectively used to analyze the influence of aggregate morphology on mixture performances. In order to explore the generation method of aggregate for DEM and the application scope of DEM, the development of DEM and aggregate generation method is summarized in this paper. The process of aggregate generation is reviewed in two steps: shell construction and the model filling. User-defined and external import methods are reviewed in shell construction. Internal filling method, equal size particle filling and other filling methods are reviewed in model filling section. Various examples and principles for each method are separately summarized in the paper. Lastly, the section of test and application is used to verify the virtual experiments with different aggregates can obtain more material motion phenomena and provide more research data. This paper provides a theoretical and technical benchmark for future numerical simulation in road engineering. [ABSTRACT FROM AUTHOR]

Faced with complex air pollution and traffic congestion, the road area ratio has gradually gained great importance in society and government. It is the ratio introduced from the field of road design and road engineering, but to study the efficiency of city planning and transportation recently. However, few studies have been conducted to study the relationship between urban congestion and pollution in the view of improving road area ratio. This paper investigated the effect of increasing the relative capacity of urban roads, i.e., road area ratio, on urban air pollution using panel data from cities in China from 2006 to 2018. In addition, the road area ratio can be further decomposed to explore the inner logic of pollution from congestion. Thus, we also explored whether the insufficient network density or width caused the pollution from congestion. We found that an increasing urban road area ratio significantly reduced air pollution, regardless of whether or not the impact of surrounding cities is included. Moreover, only an increased road density can increase traffic efficiency and reduce congestion emissions, which should be the priority of future traffic construction. The effect of increasing road width is not significant. • The increase in the urban road area ratio decreases air pollution. • There exists the "neighbor effect" of pollution in urban cities. • Decomposing the road area ratio factor to road width and road network density. • Only the increased road network density reduces traffic emissions. [ABSTRACT FROM AUTHOR]

The high-modulus asphalt mixture produced by hard asphalt has played a good role in reducing asphalt pavement rutting and improving pavement durability. It was widely used in the construction of various levels of road engineering in Europe. However, low-grade hard asphalt was rarely used in road engineering in China, and the use of hard asphalt for the design and construction of high modulus asphalt mixtures lacks sufficient engineering experience. Considering the above issues, comparative research on the performance of Chinese and French low-grade hard asphalt and mixture was carried out. In this paper, the performance of French 15# hard asphalt commonly used for EME (Enrobés à Module Elevé Class) high modulus asphalt mixture and China 15# hard asphalt was analyzed comparatively, where six typical high modulus asphalt mixtures corresponding to two low-grade hard asphalts were designed referring to the design requirements of French high modulus asphalt mixtures. The road performance of a high-modulus asphalt mixture was evaluated to verify the feasibility of its application in engineering. The research results show that the performance indicators of both Chinese and French asphalts meet the requirements of binder materials used in high modulus asphalt mixtures, and the performance of their corresponding mixtures of the two asphalts also meet the specifications of high modulus asphalt mixtures. However, the two asphalts and the performance of their corresponding mixture are slightly different. The high modulus asphalt mixture of Chinese low-grade hard bitumen can be used well in road engineering applications in China. It can strongly promote the wide application of high modulus asphalt mixture in China. [ABSTRACT FROM AUTHOR]

In the French high-modulus asphalt mixture design system, the complex modulus of the mixture under the conditions of 15 °C and 10 Hz is taken as the design index. However, in China, the dynamic modulus under the conditions of 15 °C, 10 Hz, 20 °C, 10 Hz and 45 °C, 10 Hz was taken as the stiffness modulus index of high-modulus asphalt mixture. The difference in modulus values between the two systems caused the pavement structure layer to be thicker and the construction cost to be higher in China. In order to find out the appropriate modulus value of high-modulus asphalt mixture suitable for China's modulus parameter conditions to better carry out the reasonable design and evaluation of high-modulus asphalt mixture in China, the modulus of four types of high-modulus asphalt mixtures under the two systems through the two-point bending complex modulus test of the CRT-2PT trapezoidal beam and the SPT uniaxial compression dynamic modulus test were analyzed in this paper. Under the premise of meeting the stiffness modulus index of the French high-modulus asphalt mixture, the relationship conversion models between the dynamic modulus and complex modulus of high-modulus asphalt mixture under different temperatures were established. According to the conversion models, the design evaluation value range of dynamic modulus suitable for China's condition was recommended. It is recommended that the dynamic modulus of China's high-modulus asphalt mixture at 15 °C and 10 Hz is not less than 16,000 MPa, the dynamic modulus at 20 °C and 10 Hz is not less than 14,000 MPa, and the dynamic modulus at 45 °C and 10 Hz is not less than 2500 MPa. Five kinds of high-modulus asphalt mixtures used in actual road engineering were tested to verify the reliability of the recommended dynamic modulus values based on the modulus conversion model, and the results are consistent with the recommended value range of the model. [ABSTRACT FROM AUTHOR]

The design parameters are one of the important factors to ensure the quality of asphalt pavement design. In "Highway Asphalt Pavement Design Specification" (JTGD50-2017), the stander of China, used the asphalt mixture anti-pressure resilience modulus at a single temperature of 20 °C as the design metrics. However, asphalt mixture, as a sticky-bullet plastic material, shows different mechanical properties at different temperatures. China is a vast territory, and there are great differences between the high and low temperature value (m and n) of each region. Therefore, it is unreasonable to design asphalt pavement only with the asphalt mixture anti-pressure resilience modulus value at 20 °C. Studies show that the design parameters using PG technology can improve the high temperature anti-rutting and low temperature cracking performance of asphalt pavement. [ABSTRACT FROM AUTHOR]

The expansion of road networks in emerging economies such as China causes significant greenhouse gas (GHG) emissions. This development is conflicting with China's commitment to achieve carbon neutrality. Thus, there is a need to better understand life cycle emissions of road infrastructure and opportunities to mitigate these emissions. Existing impact studies of roads in developing countries do not address recycled materials, improved pavement maintenance, or pavement-vehicle interaction and electric vehicle (EV) adoption. Combining firsthand information from Chinese road construction engineers with publicly available data, this paper estimates a comprehensive account of GHG emissions of the road pavement network to be constructed in the next ten years in the Shandong province in Northern China. Further, we estimate the potential of GHG emission reductions achievable under three scenario sets: maintenance optimization, alternative pavement material replacement, and EV adoption. Results show that the life cycle GHG emissions of highways and Class 1–4 roads to be constructed in the next 10 years amount to 147 Mt CO2-eq. Considering the use phase in our model reveals that it is the dominant stage in terms of emissions, largely due to pavement-vehicle interaction. Vehicle electrification can only moderately mitigate these emissions. Other stages, such as materials production and road maintenance and rehabilitation, contribute substantially to GHG emissions as well, highlighting the importance of optimizing the management of these stages. Surprisingly, longer, not shorter maintenance intervals, yield significant emission reductions. Another counter-intuitive finding is that thicker and more material-intensive pavement surfaces cause lower emissions overall. Taken together, optimal maintenance and rehabilitation schedules, alternative material use, and vehicle electrification provide GHG reduction potentials of 11%, 4%–16% and 2%–6%, respectively. • Road construction implies significant amounts of GHG emissions. • China's road expansion plans are at odds with its target of GHG neutrality. • We assess GHG emissions of Shandong's roads to be constructed through 2030. • We combine life cycle assessment based on primary data with a new optimization model. • Individual mitigation measures can reduce life cycle GHG emissions by up to 16%. [ABSTRACT FROM AUTHOR]

In order to evaluate the energy consumption and emission reduction effect of warm mixed asphalt (WMA) comprehensively and precisely, a novel evaluating method of the effect of WMA on emission and energy consumption of asphalt pavement construction was established and applied on the road construction project in northeast region of China. Considering the production of asphalt mixture and construction process of road engineering, a series of evaluating indices were selected and divided to the Level I and II indices respectively for establishment of evaluating system. Then, the level ranking intervals of Level I and II indices were confirmed based on the Hierarchical cluster method and Bayesian method. Finally, the single index evaluation (SIE) and multi-objective comprehensive evaluation (MOCE) methods were combined to evaluate the reducing effect of WMA on the emission and energy consumption during the highway construction process of project in northeast region of China. The results indicated that i. target WMA could achieve excellent reduction effect on COx and the reduction rate was above 60% and also promote the reducing effect on NOx and SO2 emitted during the production process of asphalt mixture. ii. The improving effect of WMA on emission was mainly reflected in the production stage of asphalt mixture rather than construction stage. iii. The application of WMA could help saving energy consumption obviously in transportation and onsite construction of asphalt mixture. This evaluating index system and method could provide reference for the reduction effect evaluation of WMA in road construction, which could help promoting the wide application of WMA in further road construction project. [ABSTRACT FROM AUTHOR]

The resonant compaction method using a crisscross-shaped probe was implemented in highway engineering projects for eliminating liquefaction in the east coastal region of China. To evaluate the compaction effectiveness in the treatment of liquefiable sand deposits with clay lenses, seismic piezocone tests (SCPTUs) and standard penetration tests (SPTs) were performed, as well as excess pore water pressure measurements. The results showed that the cone stress, sleeve friction, shear wave velocity and SPT blows increased due to vibratory compaction, and the soil liquefiable potential was eliminated. The execution of projects was highly efficient due to the simple compaction procedure and the quick dissipation of excess pore water pressure. However, the existence of a clay lens reduced the compaction effectiveness, particularly the development of SPT blows. Nevertheless, the resonant compaction method was still applicable for the treatment of soils with low to mild liquefaction levels and provided an alternative soil liquefaction countermeasure with remarkable benefits in efficiency and convenience. [ABSTRACT FROM AUTHOR]