Mechanical Properties of Asphalt Pavement Structure in Highway Tunnel

A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles.The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer,the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the as- phalt layer were calculated.The influencing factors such as double-wheel weight;asphalt layer thickness;base course stiffness modulus and thickness;and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.

Damage Effects of Overload Axes on Pavement Structures

This paper established the axle load distribution model of overload axes by practical axle-meter investigations. To study the effects of overload axes on pavement distress, deflection and deflection basin tests with axle load from 60kN to 190kN were conducted on different pavement structures. The relationship between axle load and its deflection as well as its deflection basin curvature was obtained by statistical analyses. A methodology for deriving the equivalent conversion factors of overload axes to equivalent standard axle loads (ESAL) of 100kN is developed, obtaining the relationship between the equivalent conversion factors and the axle loads. Comparing the calculated defiections with the measured deflections, that elastic layered system theory is suitable for analyzing overload vehicles was verified. Consequently, the stresses and strains caused by overload axes were calculated by elastic layered system theory. The results showed that overload axes led to greater stresses and strains causing premature pavement fatigue distress. To guarantee the expected performance in overload axes pavement, the structure thickness needed increasing was obtained. The results are of referential values in the control of semi-rigid pavement overloadings.

Study of the Influence of Groundwater Table in Mechanical Behavior of a Full-Scale Pavement Structure Modeled in a Test-Pit

The mechanical characteristics of road pavement layers are influenced by moisture conditions. Drying and wetting change the moisture content of the materials used in pavement structures, consequently affecting the mechanical response. An experimental program was conducted to evaluate elastic deformations of a road pavement structure utilizing repetitive rigid plate load tests in a model test-pit facility. A typical Brazilian pavement （a multilayer system composed of a concrete asphalt and coarse base, and subbase） was simulated in this test-pit with devices for measuring humidity （TDR （time domain reflectometry）） and suction （tensiometers） installed every 20.0 cm along the profile. A pair of displacement transducers was attached on the surface of the pavement structure to record deformations due to dynamic loads. Two levels of groundwater table were analyzed, verifying that the pavement structure displacement increases with groundwater table growth. The structural response was evaluated and compared in physical and numerical models, and the results confirmed that the higher groundwater levels caused the greatest pavement displacements.

Structural Design of Roadbed and Pavement in Transition Section of Roads and Bridges

As the lifeline of social development,road and bridge projects are the main channel to realize resource transportation and economic circulation.Ensuring the quality of road and bridge project construction is crucial for the development of society,the economy,and people’s livelihoods.This paper studies the design of roadbed pavement structures in road and bridge transition sections.It aims to provide technical references and significance for China’s road and bridge engineering design and construction units,promoting scientific and standardized design in these actions.This will contribute to the safety and stable operation of road and bridge projects,offering effective technical support.Furthermore,it seeks to foster the sustainable and healthy development of China’s road and bridge engineering on a macro level.

Adaptability evaluation of pavement structure to replacement treatment subgrade of black cotton soil

Aiming at the typical engineering problem of black cotton soil(BCS)subgrade under the alternation of dry and wet climate in the region of Nairobi,Kenya,this paper takes the pavement structure as the research object,and the numerical calculation model of BCS subgrade is established based on the consolidation coupling theory of unsaturated soil.Taking the modulus and thickness of the subbase as variables,the deformation characteristics and additional stresses of different pavement structures are analysed.Then the adaptability of different pavement structures to replacement treatment subgrade of BCS is evaluated by gray incidence decision analysis method.The results show that whatever the pavement structure is,neither subgrade modulus nor thickness is sensitive to the pavement surface deformation,and the deformation differences between each pavement structure are more obvious in wet season;the additional stress at control layer bottom and pavement surface decreases with the increase of subbase modulus,whereas the stress may increase at subbase bottom;the additional stress at subbase bottom,control layer bottom and pavement surface all decreases with the increase of subbase thickness for pavement Structure I and II.For pavement Structure III,the change of subbase thickness is not sensitive to the additional stress at the control layer bottom and pavement surface,whereas the stress at subbase bottom increases with the increase of subbase thickness.It is concluded that the most adaptable structure is pavement Structure I,which can minimize the comprehensive level of pavement settlement and additional stress.

A systematic review of steel bridge deck pavement in China

As an important part of steel bridge deck,the engineering quality and service condition of steel bridge deck pavement(SBDP)directly affects the capacity and operational efficiency of the bridge.This paper reviews the history of the development of SBDP in China over the past 20 years from the exploration stage,rapid development stage and prosperity stage.The development and application of SBDP at different stages are discussed in terms of materials,structure,design,performance evaluation,maintenance and rehabilitation,respectively.The advantages and disadvantages of different pavement materials and structures,and the application of different research methods are summarized.The review shows that the improvement of pavement materials and structures and the development of new materials should be further studied on the multi-scale to enhance the durability of pavement materials,so as to extend the service life of pavements.The design method of SBDP related to the synergistic effect of vehicle,pavement and bridge should be established,and the design concept and method standard of rigid base pavement structure should be improved and formulate a complete design standard.In addition,multi-disease intelligent identification system and equipment should be studied to track the entire course of disease development in real time.And it is necessary to develop appropriate algorithms to select and classify the complex data of disease and maintenance history.

Mechanistic-empirical pavement design guide(MEPDG):a bird's-eye view

Past editions of the American Association of State Highway and Transportation Officials （AASHTO） Guide for Design of Pavement Structures have served well for several decades; nevertheless, many serious limitations exist for their continued use as the nation＇s primary pavement design procedures. Researchers are now incorporating the latest advances in pavement design into the new Mechanistic-Empirical Pavement Design Guide （MEPDG）, developed under the National Cooperative Highway Research Program （NCHRP） 1-37A project and adopted and published by AASHTO. The MEPDG procedure offers several dramatic improvements over the current pavement design guide and presents a new paradigm in the way pavement design is performed. However, MEPDG is substantially more complex than the AASHTO Design Guide by considering the input parameters that influence pavement performance, including traffic, climate, pavement structure and material properties, and applying the principles of engineering mechanics to predict critical pavement responses. It requires significantly more input from the designer. Some of the required data are either not tracked previously or are stored in locations not familiar to designers, and many data sets need to be preprocessed for use in the MEPDG. As a result, tremendous research work has been conducted and still more challenges need to be tackled both in federal and state levels for the full implementation of MEPDG. This paper, for the first time, provides a comprehensive bird＇s eye view for the MEPDG procedure, including the evolvement of the design methodology, an overview of the design philosophy and its components, the research conducted during the development, improvement, and implementation phases, and the challenges remained and future developments directions. It is anticipated that the efforts in this paper aid in enhancing the mechanistic-empirical based pavement design for future continuous improvement to keep up with changes in trucking, materials, construction, design concepts, computers, and so on.

The Application of Impact Echo Scanning on Nondestructive Test of Pavement

A new nondestructive test method-Impact Echo Scanning was introduced. Application of this method on pavement structure test was discussed. A method to increase the measurement accuracy of the test on multi-layers was proposed, and was verified by field test. The test results show that the basic structural information can obtained rapidly and accurately by 3-D scanning of the impact echo system.

A New French Rational Design Method for Airfield Pavements

The aim of this paper is to present the results of a long-term research project consisting in the elaboration of a new rational airfield pavement design procedure applied to flexible pavements. The described methodology is based on the principles and the feedback obtained from the highway pavement design process which has been applied for more than 30 years in France as well as in many other countries. Adaptations to airfield pavements have been made, including features such as accurate traffic description, consideration of lateral wander of aircrafts for instance. The results of these developments have led to a new methodology which enables optimizing pavement designs by considering various input parameters such as the type of pavement section （runway, taxiway or apron）, the material properties and the temperature. The complete description of this method is available in the new pavement design manual and it is implemented in the dedicated software Aliz6-Airfield Pavement.

Concept Paper： Developing Pavement Structural Deterioration Curves

A SN （structural number） can be calculated for a road pavement from the properties and thicknesses of the surface, basecourse, sub-base and subgrade. Historically, the cost of collecting structural data has been very high. Data was initially collected using Benkelman Beams and now by FWD （falling weight deflectometer）. The structural strength of pavements weakens over time due to environmental and traffic loading factors but due to a lack of data, no structural deterioration curve for pavements has been implemented in a PMS （pavement management system）. IRI （international roughness index） is a measure of the road longitudinal profile and has been used as a proxy for a pavement’s structural integrity. This paper offers two conceptual methods to develop PSDC （pavement structural deterioration curves）. Firstly, structural data are grouped in sets by design ESA （equivalent standard axles）. An ISN （“initial” SN）, SNI （intermediate SN） and a TSN （terminal SN）, are used to develop the curves. Using FWD data, the ISN is the SN after the pavement is rehabilitated （Financial Accounting “Modern Equivalent”）. Intermediate SNIs, are SNs other than the ISN and TSN. The TSN was defined as the SN of the pavement when it was approved for pavement rehabilitation. The second method is to use TSD （traffic speed deflectometer） data. The road network already divided into road blocks, is grouped by traffic loading. For each traffic loading group, road blocks that have had a recent pavement rehabilitation, are used to calculate the ISN and those planned for pavement rehabilitation to calculate the TSN. The remaining SNs are used to complete the age-based or if available, historical traffic loading-based SNIs.

Review and evaluation of cold recycling with bitumen emulsion and cement for rehabilitation of old pavements

The article presents Polish experience with cold recycling of asphalt pavements with the usage of bituminous emulsion and cement. In the 1990 s numerous roads in Poland required immediate reinforcement due to their significant degradation. Implementation of the cold recycling technology was one of the solutions to this problem. Cold recycled mixtures contain e beside the recycled asphalt pavement and aggregate e two different types of binding agents: bituminous emulsion and Portland cement. First Polish requirements were developed in the 1990 s and were based on the Marshall test. After several years of application of these requirements, numerous transverse cracks appeared on the pavements. Field investigation showed that the frequency of transverse cracking was not uniform on all evaluated sections and that the growth rate of the number of cracks was decreasing. The main reason of extensive cracking was the overly high amount of the Portland cement and insufficient amount of the bituminous emulsion. This led to production of very stiff mixtures, with dominance of hydraulic bonds, which behaved similarly to cement-treated mixtures. The idea of flexible cold recycled base course was not utilized. This experience motivated the Polish Road Administration to develop new requirements. Second part of the article presents the new requirements for cold recycling.New test methods as well as requirements concerning resistance to frost and water action were introduced in 2013. Implementing of the new requirements resulted in significant reduction in stiffness of the MCE mixtures. Values of stiffness modulus are even three times lower, which should significantly decrease the amount of potential reflective cracks on the pavement surface. Presently two types of technology of cold recycling are used in Poland, in-place and in-plant.

Application of semi-analytical finite element method coupled with infinite element for analysis of asphalt pavement structural response

A specific computational program SAFEM was developed based on semi-analytical finite element （FE） method for analysis of asphalt pavement structural responses under static loads. The reliability and efficiency of this FE program was proved by comparison with the general commercial FE software ABAQUS. In order to further reduce the computational time without decrease of the accuracy, the infinite element was added to this program. The results of the finite-infinite element coupling analysis were compared with those of finite element analysis derived from the verified FE program, The study shows that finite-infinite element coupling analysis has higher reliability and efficiency.

Advanced industrial informatics towards smart,safe and sustainable roads:A state of the art

The road is one of the most important civil infrastructures for serving society,where its service quality and life have direct impacts on the safety and comfort of users.Therefore,road construction,condition detection and monitoring,and timely maintenance are particularly important for engineers.Many engineering applications of industrial informatics approaches,like image processing technology,widely used computer-based algorithms,and advanced sensors,have been initially and gradually applied to roads.This state-of-the-art review first summarized the research on industrial applications of advanced information technologies in recent years,while analyzing and comparing the advantages and disadvantages of each technology.Especially,five topics were focused on road construction,road maintenance with decision strategy,road structure evaluation,smart sensing in the road,and cooperative vehicle infrastructure system.It is expected that advanced industrial informatics can help engineers promote the development of smart,safe,and sustainable roads.

Potential of South African road technology for application in China

One of the main problems with roads and highways in China is the reflection cracking caused by the cement stabilized subbase layers passing through the overlying asphaltic layers. The cracks permit the ingress of moisture which softens the layers below the subbase resulting in loss of support and accelerated breakdown of the subbase layer and reduction in the tiding quality. The aim of this paper is to present the use of South African pavement design approach of deep structure and thin surfacing to overcome the existing problems. The deep pavement structure provides good long-term support and avoids the influence of moisture ingress, which means that only surfacing damage needs to be repaired. An unbound crushed stone base layer which is an integral component of the pavement structure limits reflection cracking. The paper first deals with the South African pavement design procedure and contrast this with the Chinese pavement design method. The inherent weaknesses of these methods are discussed and flowing from this discussion proposals for adapting the South African approach to China is presented. The resultant proposals have a high likelihood of success and will counteract the influences of extreme climate and rampant overloading that occurs on the Chinese roads.