Evaluating the effects of carbon black from recycled tires on subgrade stabilization, pavement design, and construction-phase CO₂ emissions

Abstract

This study has investigated the effects of subgrade stabilization using carbon black (CB) derived from recycled vehicle tires on the pavement structure, and subsequently on sustainability based on CO₂ emissions during the initial construction of the road. Soil samples (A-6 class per AASHTO) have been prepared with CB additions of 0%, 2.5%, 5%, 10%, 15%, and 20%. Tests have determined the optimal CB ratio as 10%, leading to 28%, 77%, and 186% increases in CBR values after 1, 7, and 28 days, respectively. Pavement thickness and costs have been designed using AASHTO 1993, showing that the best results depending on the curing times have been achieved with a 30.44% reduction in flexible pavement thickness and a 26.08% decrease in unit area cost, while rigid pavement thickness and unit area cost have been reduced by 9.67%. For a 1000 m × 20 m road, the most favorable cost savings depending on the curing times have been estimated at USD 62,890 for flexible pavement and USD 24,052 for rigid pavement. Sustainability analysis has indicated that the optimal outcomes depending on the curing times have included CO₂ reductions of 25.91% and 9.33% for flexible and rigid pavements, respectively, mainly due to material production, which has accounted for 67% and 95% of total emissions.