United States Department of Transportation
i
In-Situ Mechanical Characterization for Compacted Aggregates
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2018-10-01
[PDF-906.03 KB]
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Edition:Final report, May 2017 – May 2018
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Abstract:The evaluation of compacted unbound aggregate layers is perhaps the most common undertaking in transportation-related projects. The assessment of compaction compliance in engineered fills, subgrades, subbases, and bases in roadways and railways is central to ensure longevity of ground transportation infrastructure. In many cases, premature failures in roadways that originate in the unbound aggregate layers can be traced back to inadequate compaction. These failures are preventable, provided the problem areas can be identified by a suitable field test during construction. The most widely used method for compaction assessment during construction is the nuclear density gauge (NDG) test. While the device itself is easy to use, the complexity associated with the transportation and servicing of the radioactive device makes the test logistically and economically expensive. Furthermore, NDGs were designed to extract density and moisture content only, which are not sufficient to describe the mechanical performance of compacted unbound aggregates. This project was set out to identify available non-nuclear alternatives to the NDG test and evaluate if their failure to replace NDGs was traced to shortcomings that could be overcome through automation. It was found that the successful implementation of a non-nuclear, in-situ, mechanical performance evaluation test device requires satisfying the current information needs of practice in a system-wide context. Unavoidably, the device must be able to provide reliable density and moisture content measurements to fit within the established construction control regulatory framework, provide measurements of strength and stiffness to advance the state-of-the-practice, and be useful for the state department of transportation (DOT) in the transition from empirical to mechanistic analysis and design. Unfortunately, none of the available devices can provide on its own direct measurements of all of these parameters. In conclusion, automation may play a role in the design of a replacement for the NDG, but the real need lies in the development of a new transitional device that can measure density, moisture content, strength, and stiffness.
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