Browsing by Author "Chadbourn, Bruce A."

Now showing 1 - 5 of 5
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    An Asphalt Paving Tool for Adverse Conditions
    (1998-06-01) Chadbourn, Bruce A.; Newcomb, David E.; Voller, Vaughan R.; DeSombre, Rachel A.; Luoma, James A.; Timm, David H.
    Poor compaction can lead to early deterioration of an asphalt pavement. It often happens when paving occurs during adverse weather conditions. Yet, in Minnesota, paving must often occur under adverse conditions. A new tool now simulates the cooling of an asphalt mat behind the paver under a variety of environmental conditions. The software, PaveCool Version 2.0, offers users insights into how adverse climate conditions will affect their ability to produce a durable, quality road surface. Users input the type of existing surface, type of asphalt mix, and weather conditions. The output shows a cooling curve with recommended compaction starting and stopping times. Field tests confirm the value of this program as an aid to cold weather paving. A Windows program, PaveCoo12.0 runs on laptop computers (Windows 95, 98, or NT required). This report documents the study of thermal properties and compactibility of hot-mix asphalt, related laboratory tests on the thermal diffusivity and thermal conductivity of hot-mix asphalt at typical compaction temperatures, a literature review, and testing results. It also includes a copy of the PaveCaol Version 2.0 software.
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    The Effect of Voids in Mineral Aggregate (VMA) on Hot-Mix Asphalt Pavements
    (Minnesota Department of Transportation, 1999-09) Chadbourn, Bruce A.; Skok, Eugene L. Jr.; Newcomb, David E.; Crow, Benita L.; Spindle, Samantha
    This research project investigates the level of Voids in the Mineral Aggregate (VMA) in Minnesota paving projects. Researchers analyzed 10 paving projects from 1996 to determine if a VMA decrease occurred, the magnitude of the decrease, and the potential causes of the decrease. Potential causes include the generation of fines, high-production temperatures, and long storage or cure times. Three of the 10 projects had a VMA decrease of 1.9 or more. These three projects also had the highest plant temperatures and fairly long storage times, which makes increased asphalt absorption a likely cause of the VMA decrease. Five projects showed a moderate drop in VMA. Most had some increases in fines, and some had moderately high plant temperatures and storage times. The two projects with little or no changes in VMA had very little change in gradation, and moderate to low plant temperatures and storage times.
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    Initial Characterization of Subgrade Soils and Granular Base Materials at the Minnesota Road Research Project
    (Minnesota Department of Transportation, 1995-12) Newcomb, David E.; Chadbourn, Bruce A.; Van Deusen, David A.; Burnham, Thomas R.
    This research was conducted on the behavior of materials at the Minnesota Road Research Project (Mn/ROAD), the construction of which was completed in 1994. Falling-Weight Deflectometer (FWD) tests were conducted on the test sections at all stages of pavement construction (pre-base, post-base, and post pavement). Deflection values were highly variable due to variability in surface condition, soil moisture content, density, and stressdependent effects. In general, backcalculated subgrade moduli tended to increase with increasing FWD sensor offset (decreasing stress). Post-base and post-pavement testing also indicated an apparent increase in subgrade modulus relative to pre-base values. Moduli values were also determined for granular base results. These results were compared to Dynamic Cone Penetrometer (DCP) penetration index values as well as to resilient moduli values from tests conducted on subgrade and granular base materials in the lab. The backcalculated subgrade soil modulus values compared well with the laboratory resilient modulus values, but no correlation was seen between backcalculated moduli and penetration index values. The results of this testing will provide a baseline for future analysis of the test sections at Mn/ROAD.
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    Investigation of Recycled Asphalt Pavement (RAP) Mixtures
    (2002-02-01) Sondag, Michael S.; Chadbourn, Bruce A.; Drescher, Andrew
    This report presents the results of a study on recycled asphalt pavement (RAP) mixtures. The report includes a literature review on RAP and a summary of past research. The research focuses on the use of resilient modulus and complex modulus testing to compare mixtures compacted with only virgin materials to those compacted with varying amounts of RAP. The additional of RAP makes the mixture stiffer, as evidenced by an increase in resilient modulus and complex modulus measurements, according to the research. The addition of RAP also decreases the mixture phase angle, which corresponds to an increase in the elastic properties and a decrease in the viscous mixture properties. The report includes recommendations regarding the proper temperatures and loading frequencies for use in the complex modulus test. It also gives the percentage of RAP and the respective asphalt binder grade necessary to yield the stiffness similar to a virgin mixture.
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    Superpave Level One Mix Design At The Local Government Level
    (2001-07-01) Clyne, Timothy R.; Hanson, Mark P.; Chadbourn, Bruce A.; Newcomb, Dave
    This report presents the results of an investigation into the use of the Superpave asphalt mix design methodology at the local government level in Minnesota. In the project, researchers combined low-cost natural sand with locally available aggregates from four sources: limestone, quartzite, and partially crushed river gravel, and granite. They evaluated coarse and fine aggregate gradations, along with the use of two asphalt grades. It was difficult to achieve the Superpave volumetric requirements of voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) at 4 percent air voids, regardless of the gradation. A target air void content of 3 percent satisfied the VFA requirement, even though the VMA requirement could not be fulfilled. The fine aggregate gradations produced densities indicating that the mixtures might be tender during construction, but not necessarily be susceptible to rutting. The coarse-graded mixtures did not show the tenderness problem, but did show that they might be susceptible to rutting. Resilient modulus testing showed little or no difference in the mixtures, regardless of aggregate source or gradation. The difference in resilient modulus due to asphalt grade was apparent only at the intermediate temperatures, and not at the highest or lowest test temperatures. Moisture sensitivity testing showed that all the mixtures studied had adequate durability. Indirect tensile creep and APA rut testing indicated that resistance to low temperature cracking and rutting may be improved by decreasing the lower PG binder grade and increasing the upper PG binder grade, respectively.