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114 CHAPTER 4 Conclusions and Suggested Research Following the completion of this research study, conclu- proposed to quantify the material behavior. Based on a statis- sions and suggested research topics were developed and are tical analysis of the collected data, threshold values for each included in the following sections. of the four tests were proposed, as shown in Table 4.1. The long-pin shear test requirements (both number of blows and torque value) would be used to determine the 4.1âConclusions appropriate time to surface a recycled layer. The short-pin Based on the information obtained from the literature raveling test requirements (both number of blows and torque review and the online stakeholder survey, the most used value) would be used to determine the appropriate time to methods for assessing the quality of constructed recycled allow traffic on a recycled layer. Given the length of the pins, pavement layers are not adequate for determining the time the shear and raveling tests are appropriate only for recycled to opening to traffic or the time to surfacing. Assessing the layers having a thickness greater than 3 in. moisture content and density were found to be the most used tests in current practice. However, the moisture content value 4.2â Suggested Research is more of a surrogate for the amount of curing that has taken place within the recycled layer than an actual measure of One limitation of a civil engineering research study is the the curing progress. Similarly, low density is often considered ability to collect enough data on field-produced and field- to be an indicator of poor quality, and thus poor expected placed materials. During this study, the research team was performance, but high density values do not necessarily predict able to assess the properties of 16 recycled pavement sections good performance. where each section exhibited a unique combination of a During this study, a series of tests that could be used to recycling process, a stabilizing/recycling agent, the presence describe performance properties of an FDR, CIR, or CCPR of an active filler, or another property expected to influence layer were evaluated in laboratory and field settings. These the test results. The development of the threshold values for tests were assessed based on their potential to quantify each of the recommended tests was based on an analysis of expected changes in mixture properties with respect to curing the data collected. However, each project, by virtue of being time and presence of cement as an active filler, their vari- part of a constructed facility for public use, was constructed ability, and their correlation with other tests. As part of the with the best possible materials and construction practices. laboratory study, a ruggedness evaluation was conducted For the purposes of this study, it would have been beneficial and showed that certain physical dimensions of the test fix- to construct some sections purposefully having known tures and the angular rate at which the torque was applied defective material properties in addition to the two 0% binder were significant factors. During the field study, an ILS was trials. This would allow for the assessment of the response of completed. The ILS was used to develop precision statements the recommended tests to these defects. Future testing should for each of the recommended tests. Following the work in be undertaken on such materials in an effort to verify the the laboratory and the field, the study recommended that threshold values for each of the recommended tests. This the shear and raveling properties of recycled materials be verification could either be conducted on special test sec- assessed to quantify the time to opening to traffic and surfac- tions in the field or be completed as part of a typical recycling ing. Specifically, the number of blows and the torque value project where the reclaimer or cold recycler would process from a long-pin shear test and a short-pin raveling test were adjusted materials or other modifications.
115  Table 4.1.â Recommended test threshold values. Threshold Value Recommended Test (Average of Three Tests) Short-pin Number of blows 7.1 raveling test Torque, ft-lb 20.2 Long-pin shear Number of blows 19.3 test Torque, ft-lb 62.9
