GEOPOLYMER STABILIZATION OF KHON KAEN LOESS USING RICE HUSK ASH AND METAKAOLIN FOR PAVEMENT APPLICATIONS

Abstract

Loess, a highly compressible and moisture-sensitive silty soil found in Khon Kaen, Thailand, is generally unsuitable for pavement construction without stabilization. This research investigates the geotechnical performance of loess stabilized using a traditional 5% Ordinary Portland Cement (OPC) benchmark, versus geopolymer binders. The geopolymer system utilized 5% total binder (by dry mass of soil) of Rice Husk Ash (RHA) and metakaolin (MK), activated by 8M NaOH and Na₂SiO₃ (1:2 ratio). Standard tests, including compaction, UCS, CBR, and wet–dry durability, were conducted. Results showed RHA/MK additions slightly impacted compaction properties. The optimal mix, 1% RHA + 4% MK (1R4M), achieved a maximum Unconfined Compressive Strength (UCS) of 9,234.05 kPa, a 2.4-fold strength increase over the 5% cement (3833.39 kPa) reference. Durability assessment, conducted using wet–dry cycles with drying at 105°C, confirmed high strength retention (>90%). This superior performance is attributed to the optimal Si/Al ratio achieved in the 1R4M mix, which promoted the formation of a dense Sodium Aluminate Silicate Hydrate (N-A-S-H) geopolymer gel. The resulting CBR values support RHA/MK stabilization as an effective and sustainable alternative solution for pavement subgrade applications.