Unconfined Compressive Strength of Geopolymer-Stabilized Reclaimed Asphalt Pavement Incorporating Fly Ash and Water Treatment Sludge for Roadway Applications

Abstract

This study aims to investigate the unconfined compressive strength (UCS) of base course material made from reclaimed asphalt pavement (RAP) improved with geopolymer derived from fly ash and water treatment sludge. The alkaline solution, consisting of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3), was used to activate the geopolymerization reaction. The base course specimens were prepared by mixing RAP with different proportions of fly ash, water treatment sludge, and the alkaline solution. The combined weight of fly ash and water treatment sludge was fixed at 20% of the RAP weight. The fly ash-to-water treatment sludge ratio was varied at 100:0, 75:25, and 50:50 by weight. The alkaline solution had a concentration of 10 M and was mixed at NaOH-to-Na₂SiO₃ ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 by volume. The specimens were compacted using a modified Proctor test, cured at room temperature for 7 days, and then tested for unconfined compressive strength. The study found that base material specimens made from RAP combined with fly ash and water treatment sludge at a FA:WTS ratio of 100:0 for all NaOH:Na₂SiO₃ solution ratios, as well as those with a FA:WTS ratio of 75:25 using NaOH:Na₂SiO₃ solution ratios of 75:25 and 50:50, were able to develop UCS values exceeding 40 kg/cm² after 7 days of curing at room temperature. This meets the standard specified by the Department of Highways, indicating the potential for application of these materials as base layers in road construction.