PERFORMANCE EVALUATION OF THE UT AUTOMATED ROAD MAINTENANCE MACHINE
This final report mainly focuses on evaluating the overall performance of the University of Texas' (UT's) Automated Road Maintenance Machine (ARMM). First, the ARMM's man-machine-balanced control loop was further developed then rigorously tested and evaluated based on (1) accuracy, (2) time, and (3) quality of the resultant seal. For the efficiency evaluation, thirty pavement crack images, which included longitudinal, transverse, and block cracking, were collected from a UT research campus, and field trials were completed at five locations (Austin, San Antonio, Dallas, Corpus Christi, and Travis County) in the state of Texas. Several additional significant improvements were made to the ARMM during the course of this project. Second, the ARMM's productivity was estimated based on (1) the results of the efficiency evaluation of the man-machine control loop, (2) observations made during the series of field trials, and (3) a productivity model. The mathematical model that predicts the productivity of the ARMM under various work conditions was developed as a means for job estimating and for rating the performance of the ARMM. The ARMM's estimated productivity was then compared with the typical productivity rate associated with conventional crack sealing methods. Evaluation results from the field trials and implementation recommendations are also made in this final project report. It was concluded that the introduction of automated methods to the pavement crack-sealing process will improve productivity and quality and can reduce costs and safety risks. The latter is a direct result of reducing normal crew sizes of seven to eight workers to only three to four workers. The reduction in crew size and the increase in productivity of the sealing process translate directly into significant potential cost savings. By automatically recording work completed, the ARMM should help improve project controls; by its ability to work at night, the ARMM should reduce road user costs.
Evolution of an automated crack sealer: a study in construction technology development
Demographic, regulatory and competitive forces impose increasing pressures on the construction industry. Automated pavement crack sealing is a typical example of the technology developments that are emerging in response to these industry pressures. Development of automated construction technology such as the crack sealer involves several issues including the design cycle, economic feasibility analysis, financing, and implementation. An examination of these issues, using the development of the crack sealer as a case study, leads to the conclusion that revolutionary construction technology developments are feasible and that in the United States (US) they will be financed and carried out in the form of a variety of industry, government, and academic consortia.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.