Abstract

     This paper proposes an innovative seismic design approach for shallow rectangular cut-and-cover underground subway or railway stations. The traditional approach is to design rigid frame-like structures by connecting rigidly the main horizontal and vertical structural elements (side walls, top, bottom and intermediate slabs, and central columns); on the contrary, the proposed strategy consists of joining them by means of hinged and sliding connections, in order to obtain structures whose lateral stiffness is almost zero. The objective of this approach is to be able to adapt to the transverse racking motion imposed by the seismic ground motion without significantly increasing the internal forces in the structural members. The aforementioned flexibility of the joints is achieved by interposing rubber bearings between the connected structural elements. As a case study, an existing 2-story 3-bay subway station located in Southwest China is redesigned with the proposed technology; its seismic performance is numerically investigated by performing nonlinear dynamic analyses for a number of horizontal transverse input ground motions (accelerograms) representing the site seismicity. Such inputs are scaled to fit PGAs ranging from 0.1 to 0.6 g. As expected, the results of the time-history analyses reveal that the seismic damage to the structural members is significantly alleviated in the sliding-hinged alternative solution. This conclusion can be understood as a preliminary confirmation of the satisfactory seismic performance of the proposed technology.

Introduction

     The nowadays rapid development of buried structures, such as tunnels, underground parking lots, subway and railway stations, etc. provides alternatives to the insufficient ground space. Taking subway stations as an example, according to the International Association of Public Transport [1], there were 11,084 stations spreading over 13,903 km of subway operating lines at the end of 2017 in the world, and in the next few years another 1700 km were to be built. However, recent and past investigation reveals that earthquakes can damage underground stations [[2], [3], [4], [5], [6], [7], [8]]; therefore, further research is required on their seismic design.

     The traditional seismic design of underground stations is based on providing sufficient stiffness and strength to absorb the strains imposed by the seismic ground motion without excessive damage. This approach is basically correct and leads to safe constructions, but omits that earthquakes are indirect actions (i.e. imposed displacements): designing stiffer structures generates an increase of the soil-structure interaction force, thus providing little benefit (if any). Another smarter strategy is to try to reduce that force, either by lowering the lateral stiffness of the soil (locally) or the station. The first objective is achieved with seismic isolation [9,10], and the second with structural flexibilization measures [9,10]. Both approaches are briefed in the next two paragraphs, respectively.

Conclusions

     This paper proposes a new alternative seismic design solution for rectangular cut-and-cover underground stations; it consists of replacing the traditional rigid connections between the structural elements with hinged and sliding joints, as to obtain near-zero lateral stiffness. The required flexibility of the joints is achieved through the use of rubber bearings. The ensuing structures are expected to be able to accommodate the imposed seismic racking without relevant strains in the structure. As a case study, an existing 2-story 3-bay subway station located in Southwest China is redesigned with the proposed technology; its seismic performance is investigated numerically by time-history analyses for a set of input seismic accelerograms. These inputs are scaled to fit PGAs ranging from 0.1 to 0.6 g.

      The main output of this study is that the damage to the structural elements is considerably lessened in the sliding-hinged alternative solution; this trend is particularly intense for not only central columns but also structural connections. On the other hand, the acceleration and drift do not alter much; therefore, no higher damage to the acceleration and drift-sensitive nonstructural components is to be expected in the proposed alternative solution. These conclusions hold for all the considered levels of PGA. The remarks obtained can be read as a preliminary validation of the proposed seismic design approach.

Abstract

     While electrification of road transport is a key component of decarbonisation, the implications for the broader economy and related jobs remain underexplored. We quantify these impacts in the EU in a global Computable General Equilibrium (CGE) model, combining techno-economic assumptions about electric vehicles with deployment scenarios derived by energy models. We augment input-output tables underlying the JRC-GEM-E3 model with an explicit representation of vehicle manufacturing and upgrade the modelling of vehicle purchase and operation. Our findings illustrate that greater road transport electrification reduces the overall costs of climate mitigation, primarily driven by lower fuel costs for electric vehicles and a faster decline of battery costs. Transport electrification alters supply-chains and leads to structural shifts in employment from traditional vehicle manufacturing towards battery production, electricity supply and related investments. Finally, we expand the set of labour market indicators to cover skills and occupations, to refine the socio-economic assessments of climate policy.

Introduction

     Global CO2 emissions from transport have continued to rise in recent years across all modes (IEA, 2020a). In the EU, transport greenhouse gas (GHG) emissions were 33 % higher in 2019 compared to 1990 levels, while other sectors achieved emissions reductions over the same period (e.g. energy supply −39 %, industry −35 %, EEA, 2020). This is in stark contrast with the EU’s objectives of 55 % emission reductions by 2030 compared to 1990 and to achieve net zero emissions by 2050.1

     Road transport, accounting for nearly one-fifth of total EU GHG emissions, has therefore become a priority sector for climate action and a key element of the European Green Deal (European Commission, 2019). To encourage rapid emissions reductions in road transport, Europe has recently proposed new initiatives for stronger emissions standards for cars and vans, the set-up of a new emission trading scheme for buildings and road transport, as well as new regulation for alternative fuel and charging infrastructure (European Commission, 2021, European Commission, 2021).

Conclusions and policy implications

     The electrification of road transport is accelerating across the globe, with significant increases in electric vehicle market shares in China, Europe and the United States in particular (IEA, 2020c). While long-term projections on the number of EVs in the car and truck fleets vary across models and methodologies, the technology is widely expected to make up the majority of the total vehicle stock by mid-century, as a result of increasingly stringent climate policies and technology advancements, notably in batteries. Such fleet transformation in the coming three decades will be associated with large shifts in the manufacturing of motor vehicles and their supply-chain in the near-term, as well as changes in the operation of vehicles (fuel shifting, energy efficiency, maintenance schedules, etc.).

     This paper explores the macroeconomic implications of road transport electrification as a contributing policy to reaching Europe’s climate targets. We combine techno-economic assumptions about the composition and operation of the fleet with fuel consumption projections from energy system models into a set of climate mitigation scenarios with varying degrees of road transport electrification. We run these scenarios in an augmented version of the JRC-GEM-E3 model, which explicitly represents the manufacturing of BEVs as a separate economic activity from the manufacturing of conventional ICE vehicles. This new methodology allows for a more detailed analysis of macroeconomic impacts in two major ways: first the supply chain implications of the deployment of EVs can be more clearly identified than if all vehicles were produced using a single input structure. This has large implications in terms of employment, and therefore on occupations and skills. Second, this also allows for a new decomposition analysis, where the various channels of impacts from EVs on macroeconomic results can be explored. Our modelling suggests that a higher degree of road transport electrification can contribute to reducing the costs of climate mitigation policies.

Highlights

Abstract

Keywords

1. Introduction

2. Designing and calibrating public transport models

3. Optimal supply policies

4. Emerging technologies and related policies

5. Conclusions

CRediT authorship contribution statement

Acknowledgement

Appendix.

References

Abstract

Public transport provision requires substantial organisational efforts, careful planning, financial contributions from the public, and coordination between millions of passengers and staff members in large systems. Efficient resource allocation is critical in its daily operations. Therefore, public transport has been among the most popular subjects in transport economics since the infancy of this discipline. This paper presents an overview of the literature developed over the past half century, including more than 300 important contributions. With a strong methodological orientation, it collects, classifies, and compares the frequently used analytical modelling techniques, thus providing a cookbook for future research and learning efforts. We discuss key findings on optimal capacity provision, pricing, cost recovery and subsidies, externalities, private operations, public service regulation, and cross-cutting subjects, such as interlinks with urban economics, political economy, and emerging mobility technologies.

1. Introduction

Public transport, defined in this paper as high-capacity vehicle sharing with fixed routes and schedules, is the backbone of urban transport systems in global cities, especially in densely populated metropolitan areas. It is unlikely that mobility will become completely private in the near future, simply because of the inevitable traffic congestion and the difficulties of storing individual vehicles when they are not in use. In other words, even though technological development may transform the appearance of public transport, the fundamental challenge of coordinating between individual travellers who share vehicles of high capacity will remain. The purpose of public transport economics is to make this coordination more efficient, ensuring optimal resource allocation to unlock all societal benefits of mass mobility.

This work reviews more than 300 papers, including the most influential contributions that shaped our understanding of the economics of public transport over recent decades. The earliest studies date back to the 1960s and the 1970s when advanced quantitative methods were not available to calibrate disaggregate supply models, estimate sophisticated demand models, and simulate policy interventions’ impact on large urban networks. Did public transport economics significantly change over half a century? Interestingly, the main messages and policy recommendations of the economists in this field are still the same. Scale (density) economies, road pricing, substitution with underpriced car use, socially optimal subsidies, and the peak load problem are still on the research agenda in various forms, just like decades ago. However, the prevalence of popular subjects does not imply that theoretical and empirical results have achieved maximum impact on policymaking. Despite the surrounding consensus among members of the scientific community, the links between scale economies and subsidisation or the limitations of public transport pricing in congestion mitigation are not obvious in the wider transport industry, to mention only two examples. One of the challenges of public transport economics as a sub-discipline will emerge in knowledge dissemination and cross-fertilisation with related disciplines and professions. We believe that a critical overview of past research efforts is crucial in making impactful discoveries in the future.

1- Introduction

2- The new model

3- Linear stability analysis

4- Nonlinear stability analysis

5- Simulations

6- Conclusions

References

Abstract

Advanced communications technology enables us to obtain the Headway Variation Tendency (HVT) of the next moment in a car following scenario. To maximize the benefits of the new technology, we developed a new traffic flow model that takes into consideration the effect of HVT. First, linear analysis method is used to derive the linear stability condition, that determines whether the HVT can improve traffic system stability. Then, using the reductive perturbation method, a modified KdV (mKdV) equation is obtained and the kink–antikink solutions are derived. The phase diagram of driver sensitivity against equilibrium headway is also plotted by using the neutral stability line, derived from linear analysis and the coexisting line, derived from nonlinear analysis. This diagram demonstrates that HVT does have the ability to improve the stability of traffic stream. Finally, the effect of HVT is validated through numerical simulations, where it is evident that the information of HVT can smooth the traffic stream and prevent the formation of traffic congestion.

Introduction

The growing traffic jam causes excessive fuel consumption as well as emissions to the urban environment. Such adverse impacts pose a severe threat to the traffic system performance. Various traffic flow models have been developed, to explore the mechanism of traffic jam formation [1–40]. Generally, traffic flow models are divided into macroscopic models based on fluid mechanics, mesoscopic models based on gas dynamics theory and microscopic models based on self-driven particles. The macroscopic models include continuum [1–5] and lattice hydrodynamic models [6–13]. The mesoscopic models [14], as a bridge between microscopic and macroscopic models, can capture the probabilistic nature of interactions between vehicles and describe the macroscopic characteristics of the traffic system. The microscopic models investigate the movement of the individual vehicle, and mainly include cellular automata [15–19], car-following models [20–28] and application of microscopic models in various scenarios [29–34].

For sustainable pavement construction, this research paper aims to investigate the feasibility of using Waste Cooking Oil (WCO) and Waste Engine Oil (WEO) as rejuvenators on the rheological properties of aged bitumen extracted from Reclaimed Asphalt Pavement (RAP). The aged bitumen was extracted from milled RAP recruited from an old pavement. The rheological characteristics of the rejuvenated bitumen were determined by penetration, softening point, Brookfield viscosity, Dynamic Shear Rheometer (DSR), and Bending Beam Rheometer (BBR) tests. In addition, the chemical composition of virgin (control), aged and rejuvenated bitumen by WCO, and WEO was investigated using Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray (EDX). The quality of the rejuvenated bitumen was also evaluated by the Scanning Electron Microscopy (SEM) imaging technique. Based on penetration and softening point testing results, the optimum percentages of the waste oils were found to range from 3.5 to 4.0% for the WCO and from 5.5 to 6.0% for the WEO. The aged bitumen properties were significantly improved by rejuvenators as evidenced by the chemical analysis (FTIR and SEM/EDX) along with the ratio of asphaltenes to maltenes. Furthermore, the surface morphology was renovated as well as the fundamental physical properties of the rejuvenated aged bitumen. Additionally, the rejuvenated bitumen showed less tendency to short-term aging as confirmed by the DSR results. BBR results of rejuvenated aged bitumen samples exhibited comparable performance to those of the control samples at different low temperatures having a performance grade of PG 64-28. Moreover, rejuvenated 100% RAP mixes were found to cope with Egyptian requirements for heavy traffic as binder courses and medium traffic as wearing courses in terms of Marshall stability and flow. Finally, Indirect Tensile Strength (ITS) results were within the specification limits.

Introduction

Despite the limited resources, about 110 million tons of bitumen are used annually in the highway industry worldwide [1]. Bitumen is an organic hydrocarbon material with high thermal sensitivity. Exposure to elevated temperatures during mixing and placement of the Hot Mix Asphalt (HMA), and the environmental conditions throughout the pavement service life, lead to aging of the asphalt binder. The loss of volatiles and oxidation of bitumen (as bitumen is a hydrocarbon material) are the main causes of aging, which result in higher viscosity and stiffer bitumen [2]. Aged bitumen tends to lose its flexibility and turns into a brittle material that is prone to crack easily [3]. There has been an enormous increase in the use of Reclaimed Asphalt Pavement (RAP) worldwide as an economic and environmentally sound alternative for sustainable pavement construction [4–6]. However, some road authorities are hesitant in encouraging the use of RAP in pavement construction on a large scale due to some limitations. The barriers that limit the use of high RAP percentages (more than 15%) are the high variability in milling processes, mixing RAP from different sources, different properties of aged bitumen than required for virgin bitumen, in addition to one more additional material to care about during HMA manufacturing [6,7].

Icing on asphalt pavement may lead to potential hazards for driving safety. To reduce the security risk, this paper aims at preparing a hydrophobic emulsified asphalt coating on asphalt pavement by adding a hydrophobic agent (HPA, Polytetrafluoroethylene powder) to emulsified asphalt. Considering the factors influencing hydrophobic effect, such as roughness of hydrophobic agent, dosage and incorporation method, the ice-repellency of hydrophobic emulsified asphalt coating was characterized by means of contact angle. It was found the hydrophobic properties of emulsified asphalt were significantly affected by roughness, dosage and incorporation methods of HPA and the highest contact angle was 94.3
when the HPA with 1250 meshes and dosage of 15% was added by the external addition method. Through the interlayer shear test and the indoor anti-icing test, hydrophobic asphalt pavement could reduce the bond strength between pavement and ice so that the ice layer could be easily broken and cleared, and the bond strength could be reduced by about 40% at 0.3 kg/m2 dosage of hydrophobic emulsified asphalt. It was proved that the skid resistance performance of the hydrophobic emulsified asphalt coating could conform to the requirements of the specification. The addition of interfacial agent can significantly improve the adhesion between emulsified asphalt and aggregates. These findings demonstrated the potential of using hydrophobic emulsified asphalt coating on highways in adverse weather to provide better anti-icing performance and contribute to traffic safety in winter.

Introduction

After the rain and snow in winter, the accumulated water or snow on asphalt pavement is easy to freeze in the lowtemperature environment, resulting in a sharp decline in the anti-skidding performance of the pavement [1]. On the pavement with ice and snow, the emergency braking distance is greatly increased which poses a serious threat to the safety of life and property of pedestrians and vehicles even causes serious traffic congestion inducing a series of traffic accidents [2]. In view of the icing problems on asphalt pavements, the frequently-used methods of removing ice currently include artificial mechanical snow removal, spraying chloride ice-melting agents, thermal melting technology include microwave heating, thermal cables, solar energy collection technology, and electrically conductive pavements [3–11]. Nevertheless, the methods above will either aggravate pollutants, corrode metal structures, reduce the performance of asphalt binders or be quite expensive. A large number of literatures have shown that hydrophobic surfaces have good hydrophobic and anti-icing properties [12,13]. The larger contact angle and the smaller wetting lag angle can effectively make the droplets rolling and sliding on the surface of the object, thus making it difficult to freeze.

The effects of cement and emulsified asphalt contents on the performance of cement-emulsified asphalt mixture were systematically evaluated, including the indirect tensile strength, compressive strength, modulus of resilience, tensile strength ratio, dynamic stability, maximum bending strain, and Cantabro loss. In addition, the mesoscopic images and void characteristics of cement-emulsified asphalt mixtures with different material compositions were obtained, using scanning electron microscopy (SEM) and computed tomography (CT). The results indicated that at a constant cement content of 3%, when the emulsified asphalt content increased from 6% to 9%, the indirect tensile strength, compressive strength, and modulus of resilience first increased and then decreased. At a constant emulsified asphalt content of 8%, when the cement content increased from 0% to 4%, the indirect tensile strength first increased and then decreased, and the compressive strength and modulus of resilience each reached its maximum at a cement content of 3%. The addition of cement significantly improved the high-temperature stability and moisture stability of the asphalt mixture but was not conducive to its low-temperature performance. In addition, a minimum Cantabro loss was observed at a cement content between 2% and 3%. The mesoscopic void structures formed in different cement and emulsified asphalt contents also significantly affected the mechanical properties and mixture performances.

Introduction and literature review

A cement-emulsified asphalt mixture contains cement, emulsified asphalt, and aggregates, and is mixed at a normal temperature. In the mixture, the emulsified asphalt aggregates and demulsifies, and the cement hydrates, crystallizes and solidifies, forming a new engineering material [1,2]. Emulsified asphalt is liquid at normal temperature, and the process of mixing, paving and compacting with aggregate and cement would cause emulsion asphalt to demulsification [3,4]. Part of the moisture produced by the demulsification was consumed by the hydration reaction of the cement, and the other part was lost by evaporation. The asphalt and aggregate heating process were avoided throughout the construction process, thus avoiding the emission of asphalt smoke from heating, thereby greatly reduced energy consumption and carbon emissions during construction [5,6]. Therefore, it has been applied more and more in civil engineering, especially in pavement engineering. Because a cement-emulsified asphalt mixture contains both cement and emulsified asphalt, which have different engineering properties, the properties of the mixture are thus between those of cement and emulsified asphalt [7–9].

Mechanical characteristics of the asphalt binders and mixtures were enhanced by utilising modifiers. The crumb rubber modifier has been introduced to the asphalt modification as an environmentally friendly procedure of scrap tires, to improve the mechanical characteristics of the asphalt. This study aims to modify the dry method for mixing crumb rubber modifier with asphalt and aggregate based on the binder mix design. To achieve this goal crumb rubber modified asphalt mixtures were prepared and tested by applying various tests such as Marshall Stability test, indirect tensile strength test, and wheel tracking test. Three mixing methods of CRM were studied regarding evaluating the stability, rutting, and moisture susceptibility. The crumb rubber modifier dry mixing method was modified and named the complex process. Better results were achieved for enhancing mechanical properties.

Introduction

To reduce the environmental effects of roads building and maintenance, necessary to find solutions capable of increasing the performance of the pavement while decreasing the negative impacts. In this context, the utilisation of recycled materials appropriate for other re-uses must be progressed and enhanced [1,2]. The fields of application of CRM in road constructions are miscellaneous. The previous researchers validate them are as numerous as the number of positive results achieved in recycling this material [1]. The usage of the recycled rubber from the End of Life Tires into the bitumen concretes was began in the 1960s. The technology that has spread more is the so-called Asphalt Rubber (AR) one. AR binders produced with the manufacturing process innovated by Charles McDonald, and that is at the foundation of the wet process. This method began with the mix of the end of life tire ground rubber with the asphalt binders utilising mechanical stirring systems, operating at temperatures ranging between 190 and 218 C, for a time interval of 45–60 min [3–6].

High temperature in asphalt pavements often leads to rutting of asphalt pavements and heat island effects in urban areas. In this study, to improve the thermal resistance of asphalt pavement, hollow glass microspheres (HGM) modified asphalt and HGM/Styrene-Butadiene-Styrene (SBS) modified asphalt were used to prepare asphalt concrete (AC) and stone mastic asphalt (SMA) respectively. The effects of HGM on the penetration, ductility, softening point and rheological properties of asphalt binder and the cooling performance, mechanical property, high temperature stability, low temperature resistance, water stability and other properties of asphalt mixture were investigated. Finally, the composition of the thermal resistance surface layer was recommended. Results showed that, adding HGM increased the high temperature stability of both matrix asphalt and SBS modified asphalt while the low temperature performance of both the two types of asphalts decreased. For the asphalt mixture, the addition of HGM improved the cooling performance of the AC-13 mixture but had no effect on the cooling performance of the SMA-13 mixture. HGM also showed positive effects on the pavement performance of the asphalt mixtures. For the AC-13 mixture, it improved the mechanical property, high-temperature stability, low-temperature cracking resistance and immersion residue stability but had no effect on the thaw-splitting strength ratio (TSR). For the SMA-13 mixture, it improved the Marshall stability, high-temperature stability, immersion residue stability, scattering resistance while impaired the low-temperature crack resistance, TSR and anti-drainage ability. Finally, it was recommended to use 5% HGM modified AC-13 mixture as the thermal resistance surface layer.

Introduction

Due to its dark color, asphalt mixture has a high solar radiation absorption rate in the natural environment. Long sunshine exposure causes the asphalt pavement to absorb a large amount of heat, resulting in the continuous increase of the road surface temperature and rutting. As one of the most typical and extensive forms of distress, rutting reduces the comfort and safety of driving, affects the performance of asphalt pavement [1]. Besides, the high temperature of road surface also causes urban heat island effect in cities [2]. The heat accumulated due to heat island effect also leads to urban heating, aggravates air pollution and causes harm to residents’ health [3]. In order to reduce the negative impact of high temperature on the road surface, many measures have been taken.

Estimating the impact of transportation factors on environmental pressure is essential to find decarbonization pathways for the transportation sector. Existing research mainly focused on the economic impact of transportation factors, the environmental impact is not fully involved. To identify the coupling effect of transportation factors, this study explored the spillover effects of multiple factors on CO2 emission using the panel data of 30 administrative regions in China. A hybrid model combining expanded Stochastic Impacts by Regression on Population, Affluence, and Technology (STIRPAT) and Spatial Durbin Model (SDM) was used to estimate spillover effects of population, economic, technological and transportation factors on CO2 emissions. And CO2 emission was calculated by the carbon emission from fossil fuel consumption (coal, oil and gas) and cement production according to the Intergovernmental Panel on Climate Change (IPCC) accounting method. The estimation results indicate the spatial and time-lagged effects were both obvious for CO2 emission. In addition, transportation factors including the railway factor and the road factor were both found to have significant positive effects on CO2 emission, 0.344% and 0.129% influence respectively. Based on research findings three main policy implications were proposed including the joint decision-making, the cross-regional de-carbonization evaluation and the integrated management. This study not only reveals important experimental problems but expands a rigorous model specification process.

Introduction

As one of the fundamental infrastructures, transportation network has an enormous impact on local, national and international environmental and economic system (Guimera et al., 2005; Wandelt et al., 2017). With the rapid urbanization, more and more transportation infrastructures were constructed to support passenger and freight transport. According to the statistical data from the Organization for Economic Co-operation and Development (OECD), China’s passenger turnover and freight turnover volume ranked first in the world in 2015 (OECD, 2015). Huge transport capacity not only brings challenges to transportation network but impacts environmental conditions and economic activities. CO2 emission is the main environmental negative output during the expansion of transportation network coupling economic development (Xie et al., 2017). The International Energy Agency (IEA) estimates the transportation sector consumes approximately 19% global energy directly and accounts for 23% CO2 emission related to energy (Van der Hoeven, 2012). And it is predicted that CO2 emission in the transportation sector will increase by approximately 50% by 2030 (IEA, 2009). In addition, it has been proved that the transport infrastructure plays an increasingly important role in the evolution of city networks (Jiao et al., 2017), the human mobility (Lee et al., 2014) and the city accessibility (Shaw et al., 2014). Therefore, exploring the socio-environmental impacts of the transportation network is essential for understanding the role of the transportation network and finding sustainable pathways for the transportation sector.

Abstract

The objective of this study is to investigate the micro-mechanical characteristics of High Modulus Asphalt Concrete (HMAC) pavement structure under loads. The Discrete Element Method (DEM) was employed in this study to build the models for HMAC pavement and conventional asphalt pavement structures. The laboratory tests and DEM simulations of uniaxial compression tests were conducted on the materials of HMAC pavement structure layers. To simulate the mechanical behavior of the asphalt mixture, micro-parameters were adjusted to fit with the strain–stress curve results from lab-test. The displacement and stress distribution in vertical and horizontal directions, and the shear stress in the horizontal direction were analyzed for the HMAC pavement and conventional asphalt pavement. The results showed that the maximum vertical displacement of HMAC pavement (0.25–0.293 mm) was less than that of the conventional asphalt pavement (0.3–0.324 mm). The application of HMAC decreased the vertical stress in all structural layers except the upper surface layer. The HMAC decreased the horizontal stress in the subbase layer. Though the HMAC pavement had a slightly greater horizontal shear stress in the upper and middle surface layers than the conventional asphalt pavement, its shear resistance was. Therefore, the results indicated HMAC layer can enhance the resistance to deformation and reduce the rutting potential in asphalt pavement.

Introduction

High-modulus asphalt concrete (HMAC) was originated from France in 1980s to increase the rutting mitigation resistance and the stiffness of asphalt base layers [1]. Generally, there are three methods to obtained high modulus binders which contributes the most of the higher stiffness of HMAC: use hard-grade asphalt binders that have low penetration and high softening points [2]; use polymer modifier, such as SBS and lake asphalt [3–5]; use high-modulus agent [3,6,7]. HMAC shows evident higher stiffness when compared with conventional asphalt concrete. Pavements with HMAC base layers were reported to have good resistance to rutting and fatigue with the context of climate in France [7]. By applying HMAC, the thickness of the base layer can be greatly reduced while the performance remains the same. However, researchers still have great concerns on the mechanical performance of the HMAC in more inclement climate condition, especially its low temperature performance. Researchers from Spain carried out the repetitive loading axial tests at high temperature (40–45 C) and found the permanent deformation resistance of HMAC was highly related with the asphalt grade and voids contents [2,7].

The present study was designed to prepare the road base material by using electrolytic manganese residue (EMR), red mud (RM) and carbide slag (CS) as main raw materials. The mix was optimized and mechanical properties, durability, strength formation mechanism and environmental behavior were investigated. X-ray diffraction (XRD), Mercury intrusion porosimetry (MIP), 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and electron probe microanalysis method (EPMA) were used for microstructure characterization. The results show that after curing for 7 days, the EMRRM-CS exhibited the highest unconfined compressive strength (UCS), showed the best durability, the best pore diameter distribution and critical pore size. Hydration characteristics reveal that C-A-S-H gel and AFt are generated in EMR-RM-CS, which is positive to the form of UCS and durability. 29Si analysis demonstrates that the synergy of EMR, RM and CS has the best polymerized structure. Al in the hydrated pastes exists in the form of AlIV and AlVI, and one part of the dominant AlIV is activated and another one is converted to AlVI. The leaching results meet the Chinese groundwater standards which indicate that EMRRM-CS system can well solidify the heavy metals. The road base material prepared by EMR not only consumes a significant quantity of solid wastes but also provides a new idea for the synergistic utilization of solid wastes.

Introduction

Electrolytic manganese residue (EMR), red mud (RM) and carbide slag (CS) are three kinds of solid waste which are largely produced and difficult to recycle. EMR is a potentially harmful industrial solid waste, its major hazardous substances are heavy metals and ammonia nitrogen, which are harmful to the environment [1]. China is the largest producer of electrolytic manganese in the world with about 1.66Mt produced in 2018 [2]. Every ton of manganese produced generates 10–12 tons of EMR [3], implying that more than 15.5Mt EMR are produced annually. Red mud is the powder solid residue of bauxite after strong alkali leaching of alumina. For every ton of alumina produced will bring 1.0–1.8 tons of red mud [4,5]. Red mud contains a large number of strong alkaline chemicals with a pH value of more than 12 [6], and the main harmful element in RM is sodium. Carbide slag is an industrial waste produced by calcium carbide hydrolysis to prepare C2H2 gas, PVC, etc. [7,8]. The carbide slag had been identified as an industrial solid waste, which is difficult to be recycled. [9,10].

Rail fastening systems on a slab track at railway bridge ends are often damaged, which increases the maintenance costs. The serviceability evaluation of a rail fastening system on a slab track at railway bridge ends is based on the assumption that the stiffness of the rail fastening system is linear. The behavior of the rail fastening system on slab track at the railway bridge ends is studied in detail in this study. In the experimental model, the abutment and pier of the railway bridge were considered to be directly connected to two H-beams through a rail and rail fastening systems. A stiffness model of the rail fastening system for the finite-element analysis was established by performing a clamping-force test. In the finite-element analysis, the rail fastening system was considered as both linear and nonlinear stiffness models. The experimental and numerical results were very similar when the rail fastening system was considered as the nonlinear stiffness model. With the same uplift force acting on the rail fastening system, the displacement results of the nonlinear stiffness model were larger than those of the linear stiffness model. Therefore, it is necessary to employ the nonlinear behavior of the rail fastening system and investigate a displacement-based design method of the rail fastening system when evaluating the serviceability of the rail fastening system on the slab track at railway bridge ends.

Introduction

With the exponential growth of high-speed railway (HSR) networks [1–3], construction of railway bridges is constantly increasing. Because bridges are essential parts of HSR infrastructures for crossing valleys, existing train lines, and other obstacles. In addition, the application of slab track systems [4,5] to the railway bridges is constantly increasing. The slab track systems have been developed and implemented in a number of situations, including high-traffic and high-speed lines, in a number of countries. The slab track is being installed to offer increased passenger comfort and require minimal maintenance over time. In the case of railway bridges with slab tracks, vertical deformation of girders can lead to excessive rail deformation at the bridge ends, which may result in a larger load being applied to the rail fastening systems, which is in contrast to ballasted track systems. The geometric tolerances and tension and compression forces have a significant influence on the design of closed and open bridge joints for slab track [6]. Additionally, in the case of a rail fastening system with high stiffness, a large load is generated in the slab track [7]. These problems at the railway bridge ends need to be more attention as the high-speed lines increase.