Long Term Durability Studies On Chemically Treated Reclaimed Asphalt Pavement (RAP) Materials
Ganne, Vijay Krishna
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Reclaimed Asphalt Pavement (RAP) is a well known construction material which has been used in Hot Mix Asphalt (HMA) to reduce material costs and stabilizing the pavements for several years. It has been reported that out of 45 million tons of RAP produced every year in US, only 33% is being used in HMA. It is clear that a large amount of RAP produced is disposed off as a waste material in landfills. Hence, in order to utilize the maximum percentage of RAP and reduce the disposal rate, stabilized RAP can be effectively used as a base layer instead of local base material. In this way, the use of RAP in pavement construction not only reduces the project cost but also helps in conserving the naturally occurring aggregates. Recent studies have demonstrated that the RAP can be effectively used in base layers when blended with aggregate base materials and stabilized with chemical additives. The blending and stabilization of RAP has been proposed by previous researchers to improve the mechanical properties of the virgin RAP. In addition, the studies reported in the literature related to the use of RAP in base layers were based on only strength and stiffness parameters. But achievement of the specified strength does not always ensure durability. Therefore, in this research durability tests were conducted to determine the long term performance of the RAP mixtures. In order to accomplish this task, a comprehensive series of basic and engineering tests were conducted on various blended RAP mixtures at the UTA geotechnical and geo-environmental engineering laboratories. These RAP mixtures were designed based on minimum unconfined compression strength (UCS) achieved at the end of 7 day curing period. The required UCS strength for treated samples is achieved by adding different dosage levels of chemical stabilizers such as Portland cement or Class C fly ash. In this research, the RAP from three different locations in Texas was studied to account for the source variability. The basic tests conducted include the gradation, specific gravity and standard proctor compaction tests. The engineering tests consist of the strength and durability tests. Long-term durability of stabilized RAP has been studied by conducting wetting/drying cycles to replicate the moisture fluctuations in the field due to seasonal variations. Besides, the leachate studies were conducted on the RAP mixtures to study the rainfall infiltration and leachability of the chemical stabilizer in the long run from blended RAP mixture. In addition, mineralogical studies were carried out to ascertain the chemical stabilization of RAP mixtures. The results obtained from the engineering tests were compared among different RAP mixtures to identify the best performing mix. Out of several RAP mixtures studied, the RAP mixture prepared as 75% RAP mixed with 25% base material stabilized with 4% cement was identified as a best performing mixture. The 60% RAP with 40% base material was also yielded reasonably good results in this study. However, to promote the usage of higher percentage of recycled materials, 75% RAP mixture has been proposed. The mineralogical tests involving X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) studies confirmed that the necessary pozzolanic compounds were formed due to chemical stabilization of the RAP mixtures.