Use of a rubber wood fly ash-based geopolymer for stabilizing marginal lateritic soil as green subbase materials

Rubber wood fly ash (RWFA) is one of the main components of biomass ash materials. This research investigates the possibility of using RWFA geopolymer (RWFAG) to stabilize marginal lateritic soil (MLS) as green subbase materials. RWFA was used as a starting material. The studied influence factors included MLS/RWFA ratio, sodium silicate (NS)/sodium hydroxide (NH) ratio, soaked and unsoaked conditions, and curing time. The study involved testing the unconfined compressive strength (UCS), indirect tensile strength (ITS), and conducting microstructure. The test results revealed that the optimal liquid content for the MLS-RWFAG specimens ranged between 12 and 24% for all ingredients. As the RWFA content increased, the maximum dry unit weight of the MLS-RWFAG decreased due to the lower specific gravity of RWFA. The MLS-RWFAG specimen with 30% RWFA content and an NS/NH ratio of 70:30 yielded the maximum UCS and ITS. The SEM-EDS analysis demonstrated the production of C-S-H and N-A-S-H gels, resulting in a dense and homogeneous matrix in the MLS-RWFAG specimens. Considering cost-effectiveness, the optimum ingredients for the MLS-RWFAG specimen were identified at an MLS/RWFA ratio of 70:30 and an NS/NH ratio of 10:90, meeting the 7-day soaked UCS requirement for pavement subbase materials. Moreover, the CO2-eq emissions from MLS-RWFAG specimens were lower compared to those from 3% cement-stabilized MLS samples. These findings strongly support the use of RWFAG as a viable alternative to Portland cement for stabilizing MLS in subbase materials.