Charles Hope and Dr. Spencer Guthrie, Civil and Environmental Engineering
General Information about the Project
This study was funded in the spring of 2009 and commenced immediately afterward. The scope of the project included researching the effectiveness of microcracking of cement-treated bases (CTBs) in construction of asphalt-surfaced pavements. Microcracking is a method of reducing the amount of “block cracking” or “shrinkage cracking” that typically propagates up through the asphalt layer overlying a CTB layer. Microcracking involves making several passes over a newly constructed CTB with a heavy roller to induce a network of hairline cracks throughout the layer. Identifying equipment that can be used to determine how many passes are adequate was the focus of this project. The research included field work, where distress surveys were performed and extensive testing was conducted with the use of portable instruments; laboratory work, where material properties were tested in the BYU Highway and Materials Laboratory; and literature reviews, where the most recent studies on microcracking and CTB were compiled.
The project followed the time table in the original proposal. Field data were collected on Redwood Drive in Salt Lake City, Dale Avenue in Salt Lake City, and Black Butte Road near Rock Springs, Wyoming. The three portable instruments used for collecting data were the portable falling-weight deflectometer, soil stiffness gauge, and heavy Clegg impact soil tester. The field samples were collected and tested for material gradation, asphalt content, moisture content, and strength. The field data collected using the portable instruments were evaluated with an analysis of variance. Finally, a distress survey of Redwood Drive was performed in June 2009 to evaluate conditions 1 year after construction.
Discussion of Results
The distress survey showed that there were no reflective cracks in the asphalt on Redwood Drive after 1 year; therefore, microcracking has proved successful so far in eliminating reflection cracking from the CTB. Other findings from the study are that both the portable falling-weight deflectometer and the soil stiffness gauge are sensitive to microcracking, but the Clegg impact soil tester is not sensitive to microcracking. Therefore, the Clegg impact soil tester should not be used for monitoring microcracking. The laboratory results showed that the contractors did a reasonable job at following construction procedures and supported other findings relevant to microcracking of CTB layers in this research.
Scholarly Productivity
The receipt of this ORCA grant led to additional founding from the Portland Cement Association (PCA) in the amount of $20,000 for further study of the construction of CTB and the use of microcracking. The results of this research are 1) the production of a high-quality video on microcracking, 2) the future publication through PCA of two research reports on CTB construction, 3) the future publication of at least two peer-reviewed papers in the Transportation Research Record (TTR) and/or in American Society of Civil Engineers (ASCE) journals, and 4) at least two presentations involving the results from this study to students and professionals.
The instructional video produced as a result of this research was finalized in July 2009 and is currently being distributed nationally. Those benefitting from the production of the video include department of transportation (DOT) personnel; professionals in the cement and construction industry such as Geneva Rock, Holcim, Salt Lake City Corporation, etc.; and industry leaders both in academics and engineering practice.
The two reports intended for publication through PCA are full-scale research documents including several chapters each and data enhancing the cutting-edge knowledge of CTB microcracking. One of these two reports will be the basis for a M.S. thesis.
Journal paper submissions planned for 2010 will be submitted to leading journals commonly referenced by members of the pavement industry.
Two presentations on this research have already been given, one at the Utah Conference on Undergraduate Research (UCUR) and the other at the American Concrete Pavement Association (ACPA) Annual Conference. Approximately 50 attendees were present in that session at the ACPA conference, where several professionals requested additional information on the subject. The findings and video were shared at both conferences in early 2009 to students and professionals alike.
Conclusion
The ORCA grant received for this project funded research on microcracking of CTB layers and led to additional funding on the subject. The results of this ORCA grant include production of a video on microcracking, future publication of two research papers through PCA, future publication of peer-reviewed technical papers in scholarly journals, and two presentations where the results of this study were presented to students, professors, and professionals.
The recipient thanks the donors for funding this ORCA grant. The funding benefited the field of study in several ways, and the findings will soon be available in several academic reports and journals.
