Environmental impact assessment of recycled HMA with RAP materials from the rotary decomposition process compared to virgin HMA and conventional recycled HMA

Reclaimed asphalt pavement (RAP) is often utilized in asphalt concrete due to its significant environmental gains. This study focused on the environmental impact of recycled hot mix asphalt (HMA) with RAP materials from the rotary decomposition process compared to virgin HMA and conventional recycled HMA. SMA-13-, AC-16- and AC-20-type pavements were considered using the life cycle assessment (LCA) method. The energy consumption and air emissions at various phases were determined. Multiple impact categories, including the global warming potential (GWP), eutrophication potential (EP), photochemical smog potential (POCP) and acidification potential (AP), were calculated based on the life cycle inventory (LCI) data at varying phases. The LCI results showed that the recycled HMA was superior to the virgin HMA in terms of their energy consumption and CO2 emissions, with decline rates of approximately 10% for the AC-16 and AC-20 pavements and 5% for the SMA-13 pavement. In addition, the results indicated that two processes (the material transportation phase and the mixture production and transportation phase) contributed the most to energy consumption and carbon emissions, accounting for more than 83% overall. The life cycle impact assessment (LCIA) results revealed that all the impact categories of recycled HMA decreased greatly compared to those of virgin HMA, especially the GWP. After normalization and weighting, the significant impact category that should be given more attention was the GWP for all types of pavements. The monetized value results showed that it decreased by 10.92% for SMA-13Ⅱ compared to SMA-13Ⅰ, and by 20.85%, 30.74%, 19.53% and 32.17% for AC-16Ⅱ, AC-16Ⅲ, AC-20Ⅱ and AC-20Ⅲ, respectively, compared to that of the virgin HMA. Finally, the changes in the environmental impact of multi-rotary decomposition processes were also evaluated. And the environmental impact between the rotary decomposition process and the conventional recycling method was compared and discussed. The monetized values of AC-16-R-one-50% and AC-16-R-two-70% HMA were reduced by 8.2% and 22.8%, respectively, compared to AC-16-C-30% HMA.