Evaluating the Effect of Para-fiber on the Technical Properties of in Plant Hot Recycled Asphalt Mixture and Determining a Suitable Combination

Today, due to the rapid increase in the bitumen price and environmental problems, the hot mix recycling is taken into consideration in the construction of asphalt pavements. From a technical point of view, fibers are materials that improve a number of behaviors of asphalt mixtures. The aim of this research is to investigate the technical properties of reclaimed asphalt pavement (RAP) in the presence of para-fibers in order to achieve a suitable combination of these parameters. For this purpose, a new approach was utilized to design the experiment, analyze the results and choose the appropriate asphalt mixture. This approach uses a two-level factorial design in the Design Expert software environment based on desirability functions. The results showed that in the mixture containing 50% RAP and 6% bitumen, increasing the fibers from zero to 0.2% increases the Marshall strength value by 17.4% and decreases the Marshal flow value by 3.8%. In the same mixture with 4% bitumen, with the increase of fibers from zero to 0.2%, Marshall's strength and flow increase by 1.8 and 21.5, respectively. The most air voids are related to the mixtures, containing 50% RAP, 4% bitumen and 0.2% fibers. The results for selected materials showed that the suitable combination for the production of reclaimed asphalt mixtures according to the design criteria in Iran Highway Asphalt Paving Code is 6% bitumen, 50% RAP and 0.2% para-fiber.