Stabilization of demolished road materials for pavement base applications: Utilization of bagasse ash and fly ash geopolymer composite

This paper investigates the enhancement of recycled crushed rock and recycled asphalt pavement aggregates with bagasse ash (BA) and fly ash (FA) geopolymers, as pavement base materials, aiming to conserve natural resources and minimize waste. The mechanical performance and compaction workability are evaluated. BA geopolymer with 5 % BA activated with NaOH–Na₂SiO₃ at 10 and 12 M NaOH improves strength, achieving an unconfined compressive strength (UCS) of 2613–5980 kPa, whereas mixes with 8 M NaOH at low liquid contents do not meet the UCS requirement standards (≥ 2413 kPa) [1]. Partial replacement of BA with FA in the geopolymer increases the material density and enhances the geopolymer reactivity by adjusting the SiO₂/Al₂O₃ ratio and CaO content. FA contents up to 60 % of the total ash improves the UCS and reduces the alkali liquid content and NaOH concentration. Excessive FA, however, reduces the workability and strength because of insufficient alkali solution. The optimal mixes—40 % FA with 8 M NaOH and 60 % FA with 5 M NaOH—achieve UCSs of 2557 and 2667 kPa, respectively, balanced strength, energy absorption, workability time, and improved residual California Bearing Ratio index under soaked conditions ranging from 82.0 % (0 % FA) to 99.6 %. The two mixes reduce the greenhouse gas emissions by 37.8 % and 44.8 %, respectively, compared to that of the cement-stabilized virgin aggregates, while maintaining comparable costs. This demonstrates that BA–FA geopolymer-stabilized recycled aggregates are sustainable alternatives for pavement base layers.