Development in innovative characterization, modeling and simulation of pavements and materials

To understand the behavior of pavements under complicated loading conditions and maximize the benefits from advances in paving materials and other disciplines, innovations in numerical modeling, laboratory testing, and new construction technologies have been explored to meet these challenges (Al-Qadi et al. 2004, Wang et al. 2007, Kringos et al. 2008, Huang et al. 2009). This special issue includes ten technical papers in these areas, which can be classified into four categories: (1) innovations in paving materials; (2) advanced pavement modeling; (3) intelligent construction technology; and (4) innovative pavement testing techniques.

Paving materials

In this category, three papers were included, covering the topics of recycled concrete aggregate, colored asphalt and asphalt mastic containing fibers.

The feasibility of using RCA for various applications, such as asphalt mixture, reinforced and prestressed concrete, has been evaluated by many studies. In this special issue, Sun et al. investigated the viability of adding recycled concrete aggregate (RCA) into asphalt concrete mixture. They tested asphalt mixtures made with different portions of natural aggregate replaced by RCA. Their results showed that as the RCA dosage increases, the optimum asphalt binder content increases along with a reduced mixture bulk density. A replacement ratio of 20 to 40% RCA yields satisfactory performance. However, once the replacement ratio exceeds 50%, the performance declines drastically to an unacceptable level. Liang et al. designed an experiment to detect the flexural creep of concrete beams exposed to sealed and drying conditions. The measured creep properties were incorporated in finite element analysis to investigate the creep effect on warping deformation. It is found that creep effect is significant in slab bonded with base.

Use of asphalt is not limited to the structural pavement layer. It can also be used as functional materials in pavement marks and labels. As a type of pavement marking material, colored asphalt has gained wide application because its improves the visual setting and helps promote a safe and smooth of driving environment. This special issue presents one paper in this respect. Xu et al. looked into the preparation techniques and performance of the clear asphalt for colored micro-surfacing. They found that the properties of synthesized clear asphalt varies with the type and content of resin. In addition, the clear asphalt mixed with SBS achieved better low- and high-temperature performance than the unmodified base asphalt, while its resistance to fracture and healing with aggregate are comparable to the unmodified base asphalt.

Plain asphalt binder sometimes is not able to meet with the challenges of severe moisture susceptibility, permanent deformation, fatigue and thermal cracking. On these occasions, the inclusion of fiber into asphalt binder and mixture has been a well-recognized efficient technique. This special issue contains one paper in this regard. Zhang et al. investigated the rheological behavior and the mechanism of reinforcement of asphalt mastic containing fibers. A finite element model was developed with ABAQUS to simulate the reinforcement of the fibers. Their results indicate that the fibers have a significant reinforcing effect on the mastic, which is represented by the decreased accumulated strain and changing rate as well as increased creep stiffness moduli.

Pavement modeling

With the rapid progress in the computation capacity of modern computers, it is now possible for researchers to consider extremely complicated problems in pavement engineering on both macroscopic and microscopic scales. On the macroscopic side, in this special issue, Li et al. used finite element methods (FEM) to determine the resilient modulus of three types asphalt treated binder (ATB) course, which considered the nonlinear behavior of asphalt mixtures. They provided a user defined material subroutine to conisder the nonlinear behavior of ATB materials. Their results showed the developed FEM model was able to generate resilient modulus closely resembling to the triaxial results. Ling et al. applied extended-FEM (XFEM) in examining the effect of geotextile in controlling the thermal reflective cracking. A three-dimensional XFEM model was developed to investigate the propagation of reflective cracking and the role of geotextile in helping hinder this process. Their results showed that cracks initiate and propagate during the earlier stage as the temperature drops. Additionally, geotextile with a higher tensile strength outperforms those with a lower strength or no reinforcement in reducing crack propagation. To prevent the thermal cracking from propagating, the optimal location for installing the geotextile is the top of the existing asphalt layer.

Asphalt mixture is a composite consisting of asphalt mastic, aggregate and air voids, and it presents discrete behavior as the relative positions of particles change with the loading process. Although FEM and DEM are different in nature, they can be combined to make an even powerful tool for pavement research. In this special issue, Hou et al. presents a combined DEM-FEM model was used to study the tire-pavement friction. They investigated the tire-pavement friction by combining the finite element and discrete element methods to consider the discontinuity during the tire-pavement friction process. The FEM and DEM components of the model were connected with a layer of interface region, where the particles of the DEM model and the nodes of the FEM model are overlapped and tied directly together. Their simulation results proved that the combined DEM and FEM is a promising technique for understanding the friction behavior between vehicle tires and pavement.

Construction technology

With the advance of pavement construction machinery, it is now possible to control the pavement construction process with a high precision. Recently, a great emphasis has been placed on intelligent compaction (IC) of soil, granular base, and asphalt mixture in pavement construction. This special issue includes one technical paper on this topic. Hu et al. analyzed the relationships between different influence factors (such as temperature, underlying support, roller vibration frequency and amplitude) and the compaction meter value (CMV) from a project using intelligent compaction technology. A statistical analysis was performed first to determine the factors with significant impacts on the CMV. Along with these factors, the CMV was correlated with the modulus of asphalt layer via Witzak dymanimc modulus |E*| model. In addition, they examined the effect of underlying support of the stiffness of asphalt layer using FEM. The results indicate that after removal of the irrelevant factors, there exists a stronger correlation between the CMV and the density of asphalt mixtures.

Pavement testing and monitoring

Pavement professionals have always been striving to optimize the resource for managing existing infrastructure. One of the most important tasks for this is to monitor and evaluate the performance of the existing pavements. This special issue presents one paper on assessing pavement condition with information from the internal of the pavement system. Dong et al. attempted to establish a wireless sensing network to acquire dynamic responses of airport asphalt pavement. In their study, the Fiber Bragg Grating (FBG) sensors were utilized, and the moving average filter and Fast Fourier Transform (FFT) filter were adopted to process the digital signal from the FBG sensors. They found that the interval for wandering determination sensors depends on both the sizes of the aircraft gear and sensors. The duration of dynamic response is inversely proportional to the speed, whereas the propagation distances of stress and strain are irrelevant to the speed.

The accelerated pavement testing (APT) is a powerful tool in closing the gap between laboratory and in situ testing with realistic traffic loads and environmental exposure. Since its debut in 1909 in Detroit, APT has received extensive applications and played an important role in developing new strategies for pavement structure design and evaluating new materials. This special issue contains a technical paper in this respect. Jansen et al. presented an innovative full-scale accelerated pavement testing in Germany using a mobile load simulator (MLS). A test track was built and instrumented with pressure cells and strain gauges to monitor the structural responses from rolling-wheel loading. Several nondestructive tests, such as FWD, Ground Penetrate Radar (GPR), and cross-section profiling were also conducted. They concluded that the use of indoor and in situ APT provides another tool for addressing the challenges faced in pavement engineering.

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgments

We would like to thank Prof. Tom Scarpas and Dr. Imad Al-Qadi, the Editors in Chief of the International Journal of Pavement Engineering, and the Tylor & Francis publishing office personnel for their help and support during the production of this special issue. Special thanks are extended to all the reviewers of this special issue for their valuable comments and suggestions, which significant helped improve the quality of the technical papers.