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Cold In-Place Recycling Mix Design, In-Place Density, and Long-Term Performance in Nevada
AuthorCastro Ortiz, Jorge A.
AdvisorSebaaly, Peter E.
Civil and Environmental Engineering
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The objectives of this study were: a) analyze the impact of different variables on a performance based mix design method for cold in-place recycling (CIR), b) develop a practical method for CIR in-place density determination during construction, and c) conduct long-term performance and benefit-cost analysis of CIR pavements throughout Nevada over the period of 2000-2015.Four types of asphalt emulsions, two contents of lime slurry (4.5 and 6.0%), and two types of reclaimed asphalt pavement (RAP) gradations; a medium graded RAP according to the Pacific Coast Committee on Asphalt Specifications (PCCAS), and a non-graded RAP passing 1.0 inch sieve, were used for the mix design of CIR. The mix designs were conducted following a method using the Superpave gyratory compactor, and evaluated for their moisture susceptibility and raveling performance. Gradation plays a role on the optimum emulsion content (OEC) determination for CIR mixtures, whereas there is no noticeable increase on the performance by using 6.0 or 4.5% lime slurry.Three test methods were used to determine the in-place density of CIR pavements; the Sand Cone test method, the Balloon test method, and permeability testing using the NCAT field permeameter. Density tests were conducted on full scale CIR slabs produced in the laboratory and compared to the actual density of the compacted CIR layer obtained from core samples drilled out of the slabs. Permeability test was difficult to perform, and was discarded due to water leaks around the base of the equipment causing fines to wash away from the CIR mixture while performing the test. The best alternative to estimate the in-place air voids is the Sand Cone method coupled with measuring the bulk density of the cores using the parafilm technique. Field verification conducted on a CIR project in Fernley, Nevada, confirmed the selected test method results.Long-term performance analysis was conducted on CIR pavements constructed in Nevada during the period of 2000-2015. A total of 94 CIR pavements were identified throughout Nevada; 63 CIR pavements with AC overlays and 31 CIR pavements with surface treatments. Pavement condition index (PCI) data indicated that most of the CIR projects are in excellent or in very good condition, at the age of 15 years for CIR pavements with AC overlays and at 12 years for CIR pavements with surface treatments. The benefit cost analysis determined that pavements with lower AADT and lower CIR thickness tend to have higher benefit cost ratio, indicating a strong interaction between the structural design of the CIR pavement and its long-term performance.