Evaluation Of Resilient Modulus Of Cement And Cement-fiber Treated Reclaimed Asphalt Pavement (RAP) Aggregates
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Natural aggregates derived from a variety of source rocks have been used as a road base material. But the extraction of natural aggregates resources is increasingly being constrained by urbanization, increased costs and environmental concerns. Thus, increased amounts of reclaimed materials are being used to supplement natural aggregates in road construction. The 1993 EPA report mentioned that approximately 73 million tons of asphalt pavement material was recycled annually, which amounts to about 80% of the asphalt removed from pavements each year. The use of Reclaimed Asphalt Pavement (RAP) materials in road construction reduces both the amount of construction debris disposed of in landfills and the rate of natural resource depletion. Although RAP aggregates could be used as a base material in pavement construction applications, product variability (source dependent) and strength characteristics usually limit their application in road bases. Hence, their use should be evaluated based on their cost and strength factors. Stabilization with lime or cement allows the use of low quality RAP materials meeting the targeted characteristics. In this research, a comprehensive experimental program utilizing American Association of State Highway and Transportation Officials (AASHTO) recommended repeated load triaxial tests was designed to characterize the resilient behavior of RAP aggregates in both natural and stabilized forms. Amendments were done by using different dosage levels of Portland (Type I/II) cement and with fibrillated polypropylene fibers. Compacted aggregate specimens with no fibers (control specimens) were tested at 0, 2, and 4% dosage levels of Portland cement and those with fibers (fiber-reinforced) were tested at 2, 4, and 6% dosage levels of Portland cement. Test methods provided repeatable and reliable results. The resilient moduli of untreated aggregates varied between 180 and 340 MPa and the same of cement and cement-fiber treated aggregates varied between 200 and 580 MPa. Test results indicate that cement and cement fiber treatment provided enhancements that are statistically significant. Both two and three parameter models were used to analyze the present experimental moduli results. The structural coefficients were determined using AASHTO recommended correlation and these values were used in the development of design charts and tables for the estimation of base material thickness for a variety of variables including subgrade, traffic and category of pavements.