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1 S U M M A R Y Proposed AASHTO Practice and Tests for Process Control and Product Acceptance of Asphalt-Treated Cold Recycled Pavements Pavement recycling is a technology that can restore the service life of pavement structures and stretch available funding for pavement rehabilitation (Asphalt Recycling and Reclaiming Association 2015). In general, pavement recycling techniques remix the existing pavement material (either in situ or through a mobile plant) and reuse it in the final pavement in the form of a stabilized layer. Some of the most commonly cited benefits of using pavement recycling techniques to rehabilitate and repair asphalt concrete pavements include reduc- tions in costs, emissions, use of virgin materials, fuel consumption, construction time, and disruption to traffic. Limitations to further widespread implementation of pavement recycling processes have been reported in previous national research efforts. Among these limitations are a lack of rapid quality tests that can be used to assess the time to opening to traffic and time to surfacing a newly constructed recycled layer. This research study, which was conducted in three phases, investigated and suggest a series of tests that could be used for this purpose. Phase I included a review of the current literature related to tests that could assess the engineering properties of cold recycled materials stabilized with either emulsified or foamed asphalt, with or without a cementitious active filler. In addition, tests that were commonly used for other materials were considered. Also included as part of Phase I were an online stakeholder survey and a nationwide review of agency specifications. The stakeholder survey and specification review reinforced the concept that few tests were conducted routinely in the field that could assess desired properties beyond the currently used assessments of moisture content and density. Phase II included the assessment of identified tests in a laboratory setting on materials sampled from actual recycling projects in the United States and Canada. Sampled materials were collected and remixed in the laboratory, according to their mixture design, to produce test slabs. Early exploratory testing included development of the procedure to mix, fabricate, and then conduct testing on the test slabs at early curing times. Tests were arranged and conducted on multiple replicates to assess test variability, and multiple tests were conducted on the same slab where practicable. In addition, several exploratory tests were attempted that proved unsuitable for use with recycled materials for various reasons. The identified tests were assessed based on their potential to quantify expected changes in mixture properties with respect to curing time and presence of cement as an active filler, their variability, and their correlation to other tests. Test slabs were fabricated and tested over a series of curing times that ranged from 1 hour to 72 hours after fabrication. All curing was allowed to occur in a typical laboratory environment (that is, curing was not accelerated by heat or other methods). During Phase II, a ruggedness evaluation was completed that identified certain test fixture dimensions as being significant factors. From Phase II, selected tests were recom- mended for field study.
2 Phase III included the assessment of selected tests in a field setting where the proper- ties of materials from actual construction projects were assessed in situ. The properties of 16 recycled pavement sections were assessed where each section exhibited either a unique combination of recycling processes, a stabilizing/recycling agent, the presence of an active filler, or another property expected to influence the test result. Testing was conducted on the field projects immediately after compaction and at specified intervals up to 48 hours after compaction. The field study showed that the results of the selected tests followed trends similar to those observed in the laboratory. As part of Phase III, an interlaboratory study (ILS) was performed at a unique field-based research project. The ILS was performed in conjunction with research by others where multiple recycling processes, stabilizing/ recycling agents, and active filler contents were employed. This unique opportunity allowed an ILS to be conducted on field-produced and placed recycled materials at early ages that would not have been possible in a laboratory setting. The ILS was conducted to develop precision statements for the suggested tests. Based on the results of the testing in Phase III, the ILS, and a correlation analysis of the selected tests, a recommendation was made to use the shear and raveling properties of recycled materials in an effort to quantify the time to surfacing and time to opening to traffic, respectively. Specifically, the number of blows and torque values from a long-pin shear test and a short-pin raveling test were recommended. By use of a statistical approach, suggested threshold values for each test were developed. Draft guide specifications and preliminary draft standard practice documents were developed to assist agencies with using these new tests.