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The Effects of Reclaimed Asphalt Pavement (RAP) on the Laboratory Performances of Hot Mix Asphalts
AdvisorSebaaly, Peter E.
Civil and Environmental Engineering
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The use of reclaimed asphalt pavement (RAP) in flexible pavement surface layer has been a major sensitive issue in the construction industry. Due to limited space available in landfills, the amount of high quality virgin aggregate declines, and the high price of oil, the use of RAP in new asphalt concrete mixtures has become very attractive. This research has been conducted to study the laboratory performances of HMA mixture containing RAP, in which thermal, fatigue, rutting, moisture sensitivity, and resilient modulus characteristic were evaluated. A Marshall mix design 19 mm mixture containing 0% RAP with binder grade of PG64-22 and PG64-28NV were used as the control mixtures for evaluating properties of mixtures containing 15% and 30% RAP for three different sources of RAP which include one fresh plant waste RAP material.The effects of RAP on the laboratory performances of RAP added HMA mixture depends on type of RAP, amount of RAP, target binder grade to be produced, mixture performances. RAP binders grading, blending, and selection of new virgin binder required to blend with RAP in order to achieved target binder were performed. The final mixtures binder grades were evaluated to verify the blending chart. RAP binders were reasonably graded using standard PG binder grading system, although the NCHRP 9-12 recommends use of the modifies method for RAP binder grading. This search showed that NCHRP method of binder grading is more suitable for old aged RAPs, but not for newly produced RAP such as plant waste RAP which is less than one year old.Blending of RAP binders with virgin binders to produce target binders were successfully accomplished using blending chart method, however the results of the final target binders were found to be conservative. The conservative results might be due to grading system of 6 degree increment at higher and lower performance temperature. Mix design process of RAP added mixtures, although similar to standard mix design, are more complex and involves many calculation steps. The actual effect of RAP binder in final mix should be calculated carefully. To prevent dry mixture short term curing of the HMA mixture before compaction is strongly recommended in the Marshall Mix Design process. Regardless of sources of RAP, age, proportion (up to 30 percent in this study), RAP added mixtures can reasonably perform as better as virgin mixtures. The study of laboratory performances of RAP added mixtures have shown significant better performances in the thermal cracking and the rutting resistances. However, fatigue performance showed mixed type of results. This author is very optimistic that the fatigue performance of RAP added mixtures can be improved significantly by curing a mixture during mix design process, which ultimately increases the binder contents in the mixture and prevent from being too dry mixture.Limited research conducted during this project showed that better understanding of fatigue and rutting performances of the HMA containing RAP mixtures can be obtained if mechanistic approaches of pavement analyses are conducted. Better benefit from use of RAP can be achieved from mechanistic analysis, which generally can not be achieved from comparison of laboratory performances only. Based on this study, it has been revealed that cost ratio (with RAP/without RAP) using RAP in HMA mixtures could range from 0.97 to 0.73 when 15-30 % RAP is used. Besides the economic benefits, they also provide tremendous environmental conservation and prevention, which are immeasurable in terms of dollar value.