Soil stabilization of fly ash/ground granulated blast furnace slag based geopolymer for subgrade application

Clay soil is considered a potential natural hazard that can cause extensive damage to road pavement structure built on clay soil (collapse, crack and decreased soil strength) due to clay soil properties such as low soil strength and high soil plasticity. Geotechnical properties of problematic soils such as clay soils are improved by various methods. Soil stabilization is a process or method which improves the physical and mechanical properties of soil, such as unconfined compressive strength and Atterberg limit. Previous research reported that ground granulated blast furnace slag (GGBFS) and fly ash can be used for clay soil stabilizations, but the results of past research indicate that the road pavement construction standards remained unfulfilled, especially in terms of clay’s subgrade soil. On that basis, this research is expected to solve the problem of finding out the optimum geopolymer formulation for soil stabilization using fly ash and GGBFS based geopolymerization process in subgrade applications. This study has been conducted to investigate the geopolymerization method for soil stabilization especially subgrade application, by mixing the soil, fly ash and GGBFS with alkaline solutions, producing soil with fly ash and GGBFS based geopolymer. This research briefly describes the suitability of the fly ash and GGBFS to be used in the stabilized clay soil. Unconfined compressive strength (UCS), dynamic cone penetrometer (DCP) and California bearing ratio (CBR) were used as indicators for the strength development and hence evaluating the performance of soil stabilization based geopolymer. This research was focused on the effect of fly ash and GGBFS/alkali activator ratio and curing time on geopolymer stabilized soil. Various mix designs at different fly ash and GGBFS/ alkali activator ratio of 1.0, 1.5, 2.0, 2.5 and 3.0 were prepared with 2 conditions for UCS sample such as 1 day and 7 days curing and for DCP and CBR test were cured for 7 days. Molarity and Na2SiO3/NaOH ratio were fixed at 10 molar and 2.0 respectively. Then the UCS sample was carried out on 38 mm diameter x 76 mm height specimens. For DCP and CBR samples, the cube mould with the dimensions of 15 cm length, 15 cm width and 15 cm height were used at the field. The results showed that the highest strength obtained is 3.15 MPa with GGBFS to alkaline activator ratio of 1.5 and Na2SiO3 to NaOH ratio of 2.0 at 7 days curing time, while, according to the DCP Index result, the maximum intensity obtained was 86.22% for CBR value with GGBFS to alkaline activator ratio of 1.5 and Na2SiO3 to NaOH ratio of 2.0 at 7 days curing time. A conclusion can be drawn that the laboratory UCS test results are directly proportional to the results of the DCP and CBR test on soil stabilization based geopolymer using GGBFS and fly ash in subgrade layer applications. Furthermore, the soil stabilization using fly ash and GGBFS based geopolymer could be used as the road subgrade since the UCS, DCP and CBR test values were achieved more than the 80% and 0.80 MPa as stated in Malaysia Public Work Department (PWD).