United States Department of Transportation
i
Laboratory comparison of solvent-loaded and solvent-free emulsions
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2000-09-01
[PDF-2.26 MB]
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TRIS Online Accession Number:00800210
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OCLC Number:45182427
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Edition:Interim Report: Dec 1997 - Jan. 2000
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Abstract:Asphalt emulsions have been widely used in highway construction and maintenance since the 1920s, initially as dust palliatives and spray applications. More recently, they have been used in more diverse paving applications such as base and surface course mixes, surface treatments and maintenance activities. The Oregon Department of Transportation (ODOT) uses nearly 450,000 Mg (500,000 t) of cold mix, i.e., emulsified asphalt concrete (EAC), for construction and maintenance at a cost of approximately $10 million per year. For safety, environmental and economic reasons, the use of emulsions is likely to increase dramatically in the next ten years. The decrease in highway funding and the public's heightened environmental awareness demand innovative technology for roads of the 21 st century. Recognizing the opportunities inherent in this challenge, some commercial enterprises have already developed solvent-free alternatives. Preliminary laboratory testing of solvent-free emulsions in standard dense- and open-graded EAC mixes indicated that mechanical properties are comparable to or exceed those of conventional solvent-loaded emulsions. Accordingly, the objective of this research was to quantify the difference
between conventional solvent-loaded and solvent-free EAC as measured by indirect tensile strength. Two aggregates typically used in ODOT Regions 4 and 5 were combined with three asphalt emulsions: a conventional CMS-2S and two commercially produced solvent-free emulsions. The results from this laboratory study are extremely promising. Specimens made with solvent-free emulsions had consistently greater indirect tensile strengths than did those made with conventional solvent-loaded emulsions. Furthermore, specimens made with the solvent-free emulsions achieved that strength gain more rapidly. Minor problems with the solvent-free emulsion consistency, i.e., uniformity, were encountered, but are considered an artifact of the production process rather than a problem with the material. Given the obvious effects on mixing, coating, adhesion and strength properties, this product consistency problem should be addressed prior to field trials, the logical extension of this very promising laboratory study. To that end, experiment designs for additional laboratory testing and field trials have been proposed. The results of this and subsequent research could reduce, if not entirely eliminate the use of volatile solvents in EAC, yielding both economic and environmental benefits. Elimination of volatile solvent minimizes the fire hazard enhancing worker safety during manufacture of the emulsion and construction of the pavement section. Two-fold environmental benefits are expected with the use of solvent-free emulsions: improved air quality because of the elimination of volatile fumes; and reduction in the possibility of ground water contamination.
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