Subgrade stability of cold in-place recycled asphalt projects
Date
1998
Authors
Ellsworth, Brian James
Major Professor
Advisor
Jahren, Charles T.
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Abstract
Cold in-place asphalt recycling (CIR) has proven to be an effective technique for the rehabilitation of asphaltic concrete pavements. Though the process provides economic and performance benefits, engineers and contractors may be unfamiliar with project selection, design, and construction procedures. Some projects designed as CIR projects have failed during the construction process. After such failures occur, alternate rehabilitation methods must be used. This is expensive and inconvenient for both the contractor and the contracting agency. Subgrade stability problems can prevent a CIR project from being successful. After the existing asphalt is milled for recycling, construction equipment is only supported by the subgrade materialand the little asphalt that remains.
If the subgrade is soft, the milling machine can break through the remaining asphalt and become stuck. Soft subgrades also compromise the effectiveness of the compaction equipment. A testing method was developed to assess subgrade stability before recycling. A series of dynamic cone penetrometer (DCP) tests were conducted on a CIR project that experienced varying levels of subgrade failure. Based on this case study, it was determined that the DCP testing can discriminate between pavements that can be recycled and those that cannot. The test was also conducted on projects that experienced subgrade stability failure in the past to verify the results. After a test method was developed, tests were conducted on CIR projects that were planned for the summer of 1997 in Iowa. Most tests indicated probable success. All of the pavements were successfully recycled. This test is recommended for use as a tool during the project selection phase to identify pavements that are candidates for CIR.
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