Eshan Dave, Assistant Professor of Civil and Environmental Engineering, CEPS travels to England

Professor Dave travelled to Nottingham to organize and participate in international meetings at the University of Nottingham. Presentations given and shared centered on the subject of asphalt pavement

Performance Evaluation of Coarse-Graded Field Mixtures Using Dynamic Modulus Results Gained from Testing in the Indirect Tension Mode

Historically, asphalt mixtures in Minnesota have been produced with fine gradations. However, recently more coarse-graded mixtures are being produced as they require less asphalt binder. Thus, it is important that pavement performance for coarse gradations be evaluated. Within this research work, performance evaluation took place with the use of the Dynamic Modulus Test in Indirect Tension mode on coarsegraded mixtures consisting of field cores from 9 different pavements located in five districts of Minnesota. From each pavement’s surface layer, 3 specimens were tested at three temperatures; 0.4°C, 17.1°C, and 33.8°C each at nine frequencies ranging between 0.1 Hz and 25 Hz. Additional volumetric characterization of the field mixtures was done to determine asphalt content, air voids, and blended aggregate gradations. Asphalt binders were extracted and recovered for use in determining binder shear complex master curves. Through this information the modified Witczak model was used to create │E*│ master curves which were then compared against the indirect tension (IDT) test │E*│ experimentally created master curves. From the results the Modified Witczak Model needs to be modified for IDT collected dynamic modulus data

Comprehensive Field Evaluation of Asphalt Patching Methods and Development of Simple Decision Trees and a Best Practices Manual

The long-term performance of pothole patches largely depends on the selection of the patching method. A number of pothole patching methods are in practice in Minnesota and other nearby states. However, pavement maintenance crews often encounter problems in selecting the most appropriate patching method because proper guidelines are not available. The objective of this project was to investigate the effectiveness of different pavement patching methods and to develop simple decision trees and a best practices manual. The performance of 20 different pothole patches, which were patched with four different types of patching methods and located at five different construction sites, were monitored for approximately two years. Based on the observed performance of the pothole patches considered in this study, two forms of decision trees and a best practices manual have been developed for selecting the most appropriate patching method for a given pothole condition. The developed decision trees can be used to select the patching method based on the location of the pothole (e.g., along longitudinal joints, localized potholes, etc.), construction season, condition of the pothole, and pothole area and depth. The best practices manual provides guidelines on the selection of patching method, pothole preparation, placement of patching materials, and compaction

Disc shaped compact tension (DCT) specifications development for asphalt pavement

The disc-shaped compact tension (DCT) fracture energy test has been shown to discriminate between asphalt mixtures with respect to their thermal cracking potential. This research refines the DCT fracture energy testing procedure, identifies needed adjustments in asphalt mixture to increase fracture energy, determines the suitability of DCT-test-based parameters as indicators of reflective cracking, and proposes threshold values to lower the potential for premature reflective cracking in asphalt overlays. A number of recommendations have been developed to implement outcomes of this research as well as to fill knowledge gaps identified through this study

Development of Department Writing Guide for Civil Engineering

This paper describes the development of a writing guide for a civil engineering department. Motivation for developing a writing guide came from several sources. Freshmen enrolled in an introduction to civil engineering course turned in writing assignments demonstrating a need for improvement. The introductory course is frequently taken concurrently with a required freshman level writing class and well before a required discipline specific advanced writing class, so this was generally expected. Continued issues in junior and senior level classes, however, have clarified the need for additional program focus on written communication. Students have continually expressed frustration at having to adapt to varying lab report expectations from different faculty members and, most importantly, capstone design reports have demonstrated that student writing is not at industry expectations. The writing guide was a collaborative effort between civil engineering faculty and writing studies faculty. The initial phase focused on defining the content of the writing guide: reports (lab, project, etc.), memos, homework submittals, figures, tables, equations, professional e-mails, and references. The second phase was to develop an outline for the rubrics; the goal was for the rubrics to be general enough to be adapted by each faculty member for a given assignment, but still provide students with a consistent outline to assess their writing prior to submitting it for grade. Finally, in the third phase, the level of detail in the writing guide was discussed. In order to be useful, the writing guide was made specific enough for the students to use it to successfully complete writing assignments but general enough to allow individual faculty to adapt assignments toward the specific outcomes in each course. Above all else, the main goal of the writing guide is to prepare students for real world written communication. Therefore, it must not leave students with the impression that there is a template that can be applied regardless of audience. These concerns were considered during the development of the writing guide and will be part of in-class writing instruction within both civil engineering and writing courses. Written work will be assessed using both university and ABET assessment processes. Example work collected as part of the ABET process from the Fall 2012 semester will be retroactively assessed using the newly developed rubrics. In addition, Fall 2014 work will be assessed as it is submitted. Spring 2015 work will represent the first semester using the department writing guide. Pre-writing guide assessments will be compared to assessments of writing after the department guide is introduced. By comparing work over the next several years, senior year writing submittals will be used to determine if a greater level of competency was achieved by students exposed to the writing guide for their entire undergraduate experience as compared to students who received the writing guide late in their undergraduate career

Cracking in asphalt materials

This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.Peer ReviewedPostprint (author's final draft

Impact of Low Asphalt Binder for Coarse HMA Mixes

Asphalt mixtures are commonly specified using volumetric controls in combination with aggregate gradation limits, like most transportation agencies, MnDOT also uses this approach. Since 2010 onward, several asphalt paving projects for MnDOT have been constructed using coarser asphalt mixtures that are manufactured with lower total asphalt binder contents. Due to the severe cold climate conditions in Minnesota, there are concerns of premature cracking and inferior durability in asphalt mixtures with lower asphalt binder contents. This research project evaluated 13 low asphalt binder content mixes from 10 actual field projects to determine whether there is potential for poor cracking performance and high permeability. Assessment of field performance indicated an average of 7.75 years of life until 100% transverse cracking level is reached. The pavement structure played a significant factor in controlling the cracking rates. Thin overlays showed almost ten times inferior transverse cracking performance as compared to asphalt wearing courses on full-depth reclamation. Asphalt mixture volumetric factors did not show a statistically significant effect on cracking rates; however, the asphalt binder grade did show a strong effect. Eight out of the 13 coarse asphalt mixtures evaluated in this study have higher permeability than the typical dense graded asphalt mixtures. Performance evaluations using lab measured properties predicted poor thermal cracking performances. No discernable trends were observed between measured or predicted cracking performance and mix volumetric measures. Use of performance tests based on specifications for design and acceptance purposes is reinforced through this study

Life Cycle Costs Analysis of Reclaimed Asphalt Pavement (RAP) Under Future Climate

Reclaimed asphalt pavement (RAP) has received wide application in asphalt pavement construction and maintenance and it has shown cost-effectiveness over virgin hot mix asphalt (HMA). HMA with a high content of reclaimed asphalt (RA) (e.g., 40%) is sometimes used in practice, however, it may have significant adverse effects on the life cycle performance and related costs. In particular, challenges may arise as the life cycle performance of RAP is also affected by local climatic conditions. Thus, it is important to investigate whether it is still economic to use RAP under future local climate, with consideration of life cycle performance. A case study was conducted for various road structures on Interstate 95 (I-95) in New Hampshire (NH), USA for the investigation. The case study utilized dynamic modulus testing results for local virgin HMA and HMA with 40% RA (as major material alternatives) to predict life cycle performance of the selected pavement structures, considering downscaled future climates. Then, a life cycle cost analysis (LCCA) was considered to estimate and compare the life cycle cash flow of the investigated road structures. Responsive maintenance (overlay) and effectiveness were also considered in this study. It was found that using 40% RA in HMA can reduce agency costs by up to approximately 18% under the 2020–2040 predicted climate and NH should consider this practice under predicted future climate to reduce agency costs