DingXin Cheng

SURFACE ENERGY MEASUREMENT OF ASPHALT AND ITS APPLICATION TO PREDICTING FATIGUE AND HEALING IN ASPHALT MIXTURES

Cohesive and adhesive bonding within the asphalt—aggregate system are directly related to the surface energy of the asphalt. The thermodynamic changes in the surface energy of adhesion and cohesion are related to the de-bonding of the interface between asphalt and aggregate and to cracks that may occur within the mastic, respectively. However, it is also true that thermodynamic changes in the surface energy are required to heal a fracture between the surfaces of the asphalt and the aggregate or within the mastic. The methodology and testing protocol for measuring the surface energy of asphalt are presented. Both the surface energy of dewetting (fracture) and the surface energy of wetting (healing) can be obtained from the contact angle measurement with the Wilhelmy plate method. Ten asphalts were tested; surface energies varied substantially as a function of asphalt composition and the level of aging to which the asphalt was subjected. By using thermodynamic theory, the adhesion and cohesion bonding energy within the asphaltaggregate systems were further analyzed. This analysis has the potential to select the most compatible asphalt—aggregate combination for mixtures. The surface energy is also a very important parameter in the fatigue and healing analysis of the asphalt pavement.

Analytical Approach to Evaluating Transit Signal Priority

Abstract Successful deployment of transit signal priority (TSP) systems requires thorough laboratory evaluation before field implementation. Traffic simulation is a powerful tool in this regard; however, it requires tremendous efforts toward network coding, data collection, and model calibration. Besides, simulation models tend to be project specific, and the models developed for one project are often discarded upon the completion of that project. In this paper, it is shown that the impacts of two fundamental TSP strategies (early green and extended green) can be evaluated using an analytical approach. The impacts of the above two strategies on both the prioritized and the nonprioritized approaches are illustrated using graphical as well as analytical methods. A simulation study is then conducted for comparison analyses, followed by a statistical approach for the test of generality.

Implementing Actuated Signal-Controlled Intersection Capacity Analysis with Pedestrians

For an actuated signalized intersection, pedestrian calls are likely to affect the effective greens serving the vehicle movements, which affect the capacity and delay of the intersection. However, the current procedure in the Highway Capacity Manual 2000 (HCM) for analyzing actuated signalized intersections treats pedestrian crossing and timing statically, with either pedestrian calls at all signal cycles or no pedestrians at all. In reality, pedestrian arrivals are random events with some cycles having more pedestrians than others and other cycles having no pedestrian call at all. This paper demonstrates that the current procedure can lead to erroneous results in capacity and delay estimations. A model is introduced to overcome the shortcomings in the current procedure. The model takes into account the stochastic nature of pedestrian crossings and their effects. The model computes the probability of having pedestrian calls in a cycle and the corresponding capacities and delays for traffic movements. An implementation framework was developed to help practitioners conduct capacity analyses using the model. The models results on a semiactuated signal-controlled intersection were comparable with the results from the SimTraffic microsimulation model. The effects of pedestrians on intersection capacity and delay were analyzed using the proposed model. Depending on the pedestrian volume and traffic conditions, the current HCM procedure could produce significant error, especially when the pedestrian volume is low, because it does not consider the stochastic nature of pedestrian arrivals.

Development of Enhanced Alaska Pavement Preservation Program and Strategy Selection Guide

The Alaska Department of Transportation and Public Facilities (DOT&PF) wished to enhance its existing pavement preservation management program by using effective pavement preservation treatments for cold regions. This initiative would extend pavement life and defer the need for more costly rehabilitation. By collaborating with the California Pavement Preservation Center and the Alaska University Transportation Center, the Alaska DOT&PF recently completed a pavement preservation research project to improve its pavement preservation program for flexible pavements. Research tasks included conducting an international survey of pavement preservation in cold regions, reviewing literature on cold region pavement preservation treatments, monitoring existing preservation treatments that Alaska used, developing a pavement preservation database, and creating an online computer program for treatment selection. The database for pavement preservation treatment tracking is a web-based online program that includes standard types of pavement preservation strategies used in Alaska; pavement construction, traffic, weather, and other performance-related information; an integrated Google Map function to show the location of pavement preservation projects; and multiple pavement condition survey results with supporting documents. The strategy selection program is integrated within the pavement preservation database. The program sees results of the survey and other information on Alaska treatments to conduct treatment strategy selection and life-cycle cost analysis. Workshops have been given on preservation treatments used in cold regions and use of the database and strategy selection process. Tools developed for the Alaska DOT&PF should be helpful for long-term implementation of an effective pavement preservation program. Other agencies could learn from Alaskas experience.

Evaluation of Polyester Grout for Use in Dowel Bar Retrofit Treatments

Dowel bar retrofit (DBR) is an effective concrete pavement preservation technique to restore the load transfer efficiency at joints of the jointed plain concrete pavement. So far, more than 5 million dowel bars have been installed in the United States. Although the majority of DBR projects were successful, some have had issues, including early failures. Recently, it has been proposed that polyester grout may perform better than conventional DBR grout materials. Polyester grout is a grout using polymerized resin as a binder instead of fast setting concrete backfill material. Compared to conventional grout materials containing high alumina or magnesium phosphate materials, the polyester grout has more flexibility, better adhesion with the existing pavement, and a low viscosity for better consolidation. This paper presents the results of evaluation of performance of US 50 DBR project constructed with polyester grout in 2010 for the California Department of Transportation. In 2012, a team of researchers and engineers conducted visual inspections and nondestructive tests. Core extractions were also performed at a later date based on the visual inspection and non-destructive test results. In the laboratory, the tests included shear bonding strength tests as well as dowel bar pull out tests. The results in both the laboratory and field showed that the polyester grout has worked very well to date.

Incorporating Expert System Concept into Pavement Treatment Strategy Selection

Pavement preservation treatment selection is a complex process which involves many factors ranging from pavement engineering to economic analysis. To determine the most preferable treatment is very challenging to many pavement engineers, especially for someone with limited experience. Most states or local agencies utilize either decision trees or decision tables to assist with the treatment selection. However, there are some disadvantages of using these decision trees or decision tables. This paper proposes to incorporate the expert system concept into the pavement treatment selection process. The California Department of Transportation (Caltrans) decision tables for treatment selection have been converted to a prototype expert system which includes a user interface, an inference engine, and a knowledge base. The prototype system allows one to evaluate various treatment alternatives. The best alternative based on user provided roadway conditions and weighting scores can then be selected by the expert system. The system can help inexperienced engineers to make a better choice; it can also help streamline the decision making process for seasoned pavement engineers.