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.

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.

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.