Effect of Reclaimed Asphalt Pavement on Ontario Hot Mix Asphalt Performance
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The use of Reclaimed Asphalt Pavement (RAP), sometimes called Recycled Asphalt Pavement, in Hot Mix Asphalt (HMA) provides many benefits and has been successfully used in Ontario for several years. The production and usage of this material results in numerous environmental and economic advantages. Using RAP in HMA has various proven benefits including: reuse of high quality materials, saves on dwindling non-renewable aggregate resources, diverts large volumes of materials from overloaded landfills, reduces road building costs and contributes significantly to provincial and municipal recycling obligations. However, the usage of this material is still very conservative. Several challenges can be faced when introducing RAP in HMA, particularly in higher amounts. The characteristics of the RAP, particularly the aged (stiffer) asphalt cement (AC) in the recycled material, can affect the performance of the mix. The primary concern with increasing RAP percentages in HMA mixes are its effects on endurance against fatigue and thermal cracking. The common question in many agencies within the pavement industry is whether RAP acts as a “black rock” or the aged AC in RAP blends with the new AC in the mix. Accordingly, this research evaluated the impact that RAP in varying percentages has on a conventional Ontario mix, Superpave (SP) 12.5mm, and provided some new guidelines on the usage of RAP. Using virgin aggregates and RAP collected from a local contractor, twelve mixtures were modelled in the laboratory, with 0%, 20%, and 40% RAP contents and AC with different Performance Grade (PG). The research also examined how the addition of RAP to HMA alters the performance of the mix, and how HMA can be tested to determine the RAP content. This research intended to answer the following questions: First, can the RAP percentage be determined from the recycled hot mix asphalt characteristics or performance? And second, can the blended binder PG be deduced from performance testing of recycled hot mix? This research demonstrated that is possible to design Superpave mixes incorporating 20% RAP and 40% RAP without compromising the specified consensus properties and volumetric characteristics. Based on the results, it was determined that the performance of the recycled hot mixes regarding low temperature cracking, rutting and stiffness, which is related to the fatigue susceptibility of the mix, was simultaneously influenced by the RAP content and the virgin asphalt PG. The effect of the RAP addition was more dramatic for the mixes with virgin binder PG 52-xx than for the mixes with PG 58-xx. A method to determine the presence and quantity of RAP was formulated, and also an estimation of the performance grade of the resulting blended binder without extraction and recovery of the asphalt was possible.