Yanjun Qiu

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.

Analysis of measured strain response of asphalt pavements and relevant prediction models

Abstract In order to investigate the actual strain response of asphalt pavement under real condition, three types of asphalt pavement sections with typical surface structures are built. The effects of axle configuration, axle load, speed and testing temperature on strain response of asphalt pavement were analysed through in situ dynamic loading. Experimental results indicate that the strain response at the bottom of the asphalt surface layer increases with increasing axle load and temperature, but decreases with the rise of speed. On the other hand, the temperature exerts different influence levels on pavement sections with different structures. It is also concluded that the tandem axle load could lead to a greater strain response than that of single axle load. Applying the analysis of variance, the effects of pavement surface temperature, axle load, speed and their double interactions are studied as well. Finally, the paper proposes prediction models of the strain response at the bottom of asphalt layer by means of multivariate regression analysis.

Comparative analysis on dynamic behavior of two HMA railway substructures

A numerical analysis using a finite element program was performed on three structures: hot mix asphalt (HMA) reinforced trackbed (RACS-1), HMA directly supported trackbed (RACS-2), and traditional Portland Cement Concrete (PCC) slab track (SlabTrack). Although the comprehensive dynamic responses of RACS-1 were similar with SlabTrack, HMA layer can positively affect the stress distributions. In particular, the horizontal stresses indicate that the resilience of RACS-1 was improved relative to SlabTrack. In addition, HMA reinforced substructure has the capacity to recover the residual vertical deformation. The effective depth for weakening dynamic loadings is mainly from 0 to 2 m, this being especially true at 0.5 m. The results from the analysis show that HMA is a suitable material for the railway substructure to enhance resilient performance, improve the stress distribution, weaken dynamic loading, and lower the vibration, especially at the effective depth of 2 m. The HMA constructed at the top of the stone subbase layer allows the vertical modulus a smooth transition. In terms of the comprehensive dynamic behaviors, RACS-1 is better than SlabTrack, while the results for RACS-2 are inconclusive and require further research.

Asphalt Concrete Layer to Support Track Slab of High-Speed Railway

Asphalt concrete (AC) is a traditional material that is used to construct highway pavement and offers the advantages of good bearing capacity, waterproofing, shock absorption, and noise reduction. In recent years, AC also has been used to construct railway infrastructure as part of the rapid development of high-speed rail in China. The study presented in this paper focused on the material composition and mechanical response of railway asphalt concrete (RAC) on the basis of mechanistic models and laboratory experiments. According to the material test results, the air voids of the material RAC-25 used for railway infrastructure should be controlled from 1% to 3%. The optimal asphalt content should be obtained from parameter tests. The recommended asphalt content should be less than 5.8%. Load-bearing infrastructure with the use of RAC-25 to replace partially the surface layer of subgrade, which was a stabilized layer on top of the subgrade, may yield a better performance. This design was No. 1 asphalt concrete railway substructure (ACRS-1). On the basis of the test results, the model with a 12-cm depth of graded gravel subgrade surface layer replaced by RAC-25 showed much better capacity and stability than other models. By comparison, the model reinforced by RAC-25 showed a higher K30 value, less deformation, good temperature sensitivity, and better loading performance. In summary, the ACRS-1 reinforced by RAC-25 was found to be a suitable type of structure for high-speed railway infrastructure.

Experimental study of a new modified waterproof asphalt concrete and its performance on bridge deck

The employment of asphalt concrete on the bridge surface paving has been widely used in long-span bridges owing to its merits such as light weight, seamless, good performance and simple maintenance. Currently, three types of asphalt materials – namely Guss asphalt , stone mastic asphalt and epoxy asphalt concrete – are principally applied in bridge deck pavement. However, these asphalt pavements have their own disadvantages. In order to further enhance the overall performance of asphalt concrete and its engineering applicability on bridge surface, in this research a new modified waterproof asphalt concrete is produced. The new modified asphalt from two aspects of the asphalt binder material and mixture were developed. To evaluate the performance of the new asphalt material and verify the feasibility of its application, a series of tests on bitumen and asphalt mixture were conducted. In addition, a comparative evaluation between the newly developed asphalt mixture and traditional ones was conducted. All in all, the results of this research could make a great contribution to the application of asphalt concrete technology on bridge surface paving.

High-Order Spectral Finite Elements in Analysis of Collinear Wave Mixing

Implementing collinear wave mixing techniques with numerical methods to detect acoustic nonlinearity due to damage and defects is of vital importance in nondestructive examination engineering. However, numerical simulations in existing literatures are often limited due to the compromise between computational efficiency and accuracy. In order to balance the contradiction, spectral finite element (abbreviated as SFE) with 3 × 3 and 8 × 6 nodes is developed to simulate collinear wave mixing for 1D and 2D cases in this study. The comparisons among analytical solutions, experiments, finite element method (FEM), and spectral finite element method are presented to validate the feasibility, efficiency, and accuracy of the proposed SFEs. The results demonstrate that the proposed SFEs are capable of increasing computational efficiency by as much as 14 times while maintaining the same accuracy in comparison with FEM. In addition, five 3 × 3 nodes’ SFEs or one 8 × 6 nodes’ SFE per the shortest wavelength is sufficient to capture mixing waves. Finally, the proposed 8 × 6 nodes’ SFE is recommended for collinear wave mixing to detect damage, which can offer more accuracy with similar efficiency compared to 3 × 3 nodes’ SFE.

Measured Dynamic Response of Asphalt Pavement under FWD Load

To study the real dynamic response regularity of asphalt pavement structure under dynamic load, a road test was conducted for three types of typical asphalt pavement. Dynamic and static deflection basins were established. The characteristics of the dynamic deflection basin were studied. The set-in dynamic strain sensors at the bottom of the surface layer collected the dynamic strain response under falling weight deflectometer (FWD) load. Results show that the static deflection basin is deeper than the dynamic deflection basin, but the range of the latter is larger than that of the former. The characteristics of the two deflection basins differ. The change trends of dynamic response with an increase in FWD load reflect nonlinear characteristics. The dynamic strain of three typical asphalt pavements at the bottom of the surface layer does not induce fatigue failure in the pavement structure. The longitudinal strain is larger than the lateral strain. Different prediction models on dynamic strain on the basis of dynamic deflection basin parameters are established.

Study of Strength Forming Mechanism and Influencing Factors of Half-Warm Mix Asphalt

In order to study the strength forming mechanism and influencing factors of half-warm mix asphalt (HWMA), the stability of Marshall samples is tested under different test conditions such as gradations, asphalt quantities, forming methods, number of compaction passes, maintenance period, and forms of maintenance. The results show that (1) the suspension dense gradation is satisfactory for early strength of HWMA, and its strength varies with asphalt quantity; (2) the number of compaction passes and maintenance period are two major external factors influencing strength forming, and the increase in strength reduces significantly when the number of compaction passes on both sides increases above 130. (The Marshall samples acquire final strength in 49 days of maintenance.); and (3) both loading and maintenance time significantly affect the strength forming process. Moreover, the cohesion of the material and internal friction increase, and the Marshall samples gain strength more rapidly with both the factors. Loading and maintenance time affect the internal friction and cohesion of the material, respectively. The results of this study provide guidance for design and construction of HWMA.

Research on Dynamic Response of Pavement under Moving Vehicle Loading Using Three Dimensional Finite Element Method

To analyze the dynamic response of the pavement structure under moving vehicle loading is always a hot point in pavement engineering. In this paper, the moving vehicle has been simplified as spring-dashpot components and the pavement structure has also been discrete using three-dimension finite element model. Based on Newton iteration and central difference integration algorithm, the static and dynamic coupling reactions between pavement structure and vehicle have also been considered using finite element platform ABAQUS. The numerical results and analytic results can fit very well in static analysis, meanwhile the numerical results and experiment results can fit very well in dynamic analysis. Based on preceding verified numerical model, a few interesting phenomenon have been discovered. The pavement dynamic vertical displacement in upper layer is much higher than the situation in static analysis, because the vertical displacement is superimposed during the dynamic response analysis. Furthermore the vertical fluctuation of the vehicles bar center exists even the vehicle moving in the initial even pavement, and the inertial forces is the most important reason to induce this behavior. In the last, this paper has proposed a more accurate, fast and concrete evidence to explain the reason that the dynamic response has obvious relationship with the diseases in pavement layer.

Data needs and implementation of the Pavement ME Design

ABSTRACT Highway agencies across the United States are moving from empirical design procedures towards the mechanistic-empirical (ME) based pavement design. The Pavement ME Design presents a new paradigm shift with several important improvements, and it requires extensive data needs for full implementation. Based on extensive research conducted in the past two decades, this paper provides a comprehensive review of the data needs and processes related to the Pavement ME Design. A full spectrum of the art-of-the-state implementation activities in sensitivity analysis, climate data, traffic inputs, material characterization, and local calibration approaches and practices have been investigated. Special emphasis is on Weigh-in-Motion (WIM) data processing algorithms and software developed by the authors, and the interpretation of the damage models in the Pavement ME Design. The efforts in this paper can aid in the continuous implementation and enhancement of the Pavement ME Design.