Effect of humic acid and fulvic acid on mechanical and durability properties of geopolymer stabilized soft soil

Geopolymer with eco-friendly and excellent performance is regarded as a new generation of soil stabilizer. Although geopolymer is effective in improving the mechanical and durability properties of soft soil, the mech-anism of the influence of organic matter (humic acid and fulvic acid) in soft soil is often neglected. Therefore, in this work, the effects of different contents (0%, 0.5%, 1.5%, 2.5%, 3.5%, 4.5%, 5.5%) of humic acid and fulvic acid on the mechanical and durability properties of geopolymer stabilized soft soil (GSSS) were elucidated. The mechanical characteristics, durability and microstructure of GSSS were characterized by UCS test, sulphate so-lution attack test, XRD and SEM analysis. The samples for the UCS test were cured in a standard curing box (temperature regulated at 20 +/- 2 celcius and humidity not less than 95%) for 7 d/28 d, while the samples for the sulphate solution attack test were cured in a standard curing box for 28 d beforehand. The results demonstrated that there existed a limit content (4.5% and 3.5%) for the effect of humic acid and fulvic acid on the UCS of GSSS, respectively, beyond which the UCS of GSSS almost ceased to change with the increase of humic acid and fulvic acid contents. With the increase of organic matter content, the damage mode of GSSS changed from brittle damage to plastic damage accompanied by the decrease of peak stress. After exposure to Na2SO4 solution, the UCS deterioration rate of GSSS incorporated with fulvic acid was faster compared to humic acid when the organic matter content did not exceed 2.5%, while the opposite was true when the organic matter content exceeded 2.5%.