EFFECT OF FLY ASH GEOPOLYMER CONTENT AND ALKALI RATIO ON SILTY SUBBASE SOIL COMPACTION AND STRENGTH

Abstract

This study evaluates the compaction and strength properties of silty subbase soil treated with fly ash-based geopolymer (FAG) and determines the synergistic effects of FAG content and alkali ratio (AR) on the soil's Maximum Dry Density (MDD), Optimum Moisture Content (OMC), and California Bearing Ratio (CBR) under soaked condition. The silty subbase soil samples were treated with FAG content at 10%, 20%, and 30% by dry weight of the soil. 10 molars (M) of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃), with AR (NaOH to Na₂SiO₃) of 0.33, 1.00, and 3.00, were used to activate the FAG. Testing, such as Compaction and California Bearing Ratio (CBR), was carried out on the prepared soil samples using the guidelines indicated in AASHTO T 180 (Method D) and AASHTO T 193, respectively. Relative to untreated soil, the results showed a slight increase in MDD of about 0.65%, a decrease of about 17.34% in OMC, and a significant improvement in the CBR of about 775%. Moreover, a higher proportion of NaOH in the AR is observed to have developed a significant improvement in MDD, OMC, and CBR compared with a higher proportion of Na₂SiO₃. The extent of these improvements is influenced by the FAG content and AR, which indicates that the behavior is not governed by a single parameter but by their combined effects. Furthermore, the findings of this study present that geopolymer with fly ash is a viable, effective, and sustainable alternative to cement-based stabilization.