Evaluation of Variability in Recycled Asphalt Pavement and Development of Intelligent Software for Determining Maximum RAP Content

<div class="section abstract"><div class="htmlview paragraph">The asphalt pavement plant mixing hot recycling technology not only reduces the consumption of natural resources by recycling discarded asphalt pavement, but also effectively saves economic costs. However, the composition of recycled asphalt pavement (RAP) materials exhibits significant variability, which hinders the widespread use of RAP in recycled asphalt mixtures (RAM). To address this issue, this article evaluated the variability of RAP with different rock types and the addition of new aggregates and asphalt-aggregate ratios, and developed intelligent software to determine the maximum allowable RAP content for different road grades. At the same time, homogenization measures such as classification and stacking of RAP should be taken to increase the RAP content. The results show that Basalt RAP exhibits more significant variability in grading and asphalt-aggregate ratio compared to Limestone RAP. Additionally, the variability in RAP grading is greater than that in asphalt-aggregate ratio. There is also some fluctuation in the ratio of newly added aggregates to asphalt, with the fluctuation of new aggregates being greater than that of new asphalt. The maximum RAP content determined by intelligent software is controlled by the RAP asphalt-aggregate ratio, and due to the greater variability of basalt RAP asphalt-aggregate ratio, its determined maximum content is smaller than that in limestone RAP. In addition, the homogenization treatment of RAP can reduce the coefficient of variation of the 4.75mm, 2.36mm, and 0.075mm sieve size pass rates of RAM by 3.65%, 3.25%, and 3.31%, respectively, while reducing the coefficient of variation of asphalt aggregate ratio by 1.21%. Through this homogenization measure, the factory can produce RAM with more stable gradation and asphalt aggregate ratio.</div></div>