Determining the relationship between the percentages of reclaimed asphalt pavement used in asphalt concrete mixtures and its low temperature performance

This research intends to determine the low temperature properties of asphalt concrete mixtures containing Reclaimed Asphalt Pavement (RAP). As a part of this study, a set of asphalt concrete mixtures with varied RAP content were prepared in the laboratory, and tested along with a set of a field prepared asphalt concrete mixtures containing RAP obtained from a plant. The mixtures prepared were compacted using the Superpave Gyratory Compactor (SGC). These compacted specimens were then cut into thin beams of size 12.7 mm x 6.35 mm x 125 mm (width x thickness x length) and tested at low temperatures using a bending beam rheometer (BBR). The stiffness and creep compliance values of these specimens were obtained through the BBR testing at low temperatures of -18°C, -12°C and -24°C. Time-temperature superposition principle was applied to individual compliance values of all specimens in order to obtain a master creep stiffness curve for all asphalt mixtures tested. Using a Laplace transformation the relaxation moduli for the asphalt mixtures was predicted. With the help of the calculated relaxation moduli and the strain caused by the thermal contraction of the material in the field, the thermal stresses of asphalt concrete pavements constructed with these mixtures were determined. Following the determination of thermal stresses, a comparison study was conducted for all the percentages of RAP considered. The thermal stresses determined were used to generate plots between stress and temperature were drawn. These plots provided the critical cracking temperatures for different percentages of RAP incorporated asphalt concrete mixtures used in this study. The critical cracking temperatures, TCR of -33.4°C, -32.5°C, -31.5°C and -30°C were obtained for no RAP condition, 5% RAP, 15% RAP and 25% RAP containing asphalt concrete mixtures respectively. These results were evaluated based on the Long-Term Pavement Performance (LTTP) data obtained from Federal Highway Administration (FHWA). It was concluded that the addition of RAP would increase the critical cracking temperature, TCR and thus decrease the performance of the pavements.