The Effect of Adding Mixture of Gypsum-Lime with Geopolymer on the Properties of Swelling Soil

This study was to investigate the influence of adding optimum percentages of gypsum (G) - lime (L) mixtures (i.e. 6% lime and 4% gypsum) with three percentages of fly ash geopolymer (FAG) (i.e. 6%, 9%, and 12%) on some engineering properties of expansive soil. The tests results indicated that adding the percentages for the gypsum-lime mixture (6% lime + 4% gypsum) affected the soil’s properties by decreasing the plasticity index, swelling potential, and swelling pressure by 48.2%, 85%, and 87.9%, respectively. Adding (6% L + 4% G + 12% FAG) decreased the plasticity index, swelling potential, and swelling pressure of prepared expansive soil by about 66.1%, 96.4%, and 96.9%, respectively. The California bearing ratio increased up to 33.3% and 95.1% with the addition of (6% L + 4% G) and (6% L + 4% G + 12% FAG), respectively. Also, adding the same percentages of gypsum-lime mixture and gypsum-lime mixture with geopolymer caused increasing in Unconfined compressive strength value by 109.5% and 322.6%, respectively. The results show the significant effect of gypsum-lime mixture with geopolymer on compaction parameters of the prepared soil, so there was a decrease from 22% to 18% for the optimum moisture content and an increase from 1.473 g/cm³ to 1.516 g/cm³ for the maximum dry density.