Use of gasification fly ash, sodium carbonate, and ground granulated blast-furnace slag for soft clay stabilization

Gasification fly ash (GFA) generated from the municipal solid waste (MSW) slagging-gasification is strongly alkaline and has the potential to be used to activate ground granulated blast-furnace slag (GGBS) for soil stabilization. However, heavy metals like Pb and Zn in GFA would retard the hydration of GGBS and reduce the final strength of stabilized clay. Thus, sodium carbonate (Na2CO3) is added to mitigate the negative effect caused by heavy metals. In this study, GFA-Na2CO3-GGBS stabilized soft clay with a high initial water content was studied and compared with conventional ordinary Portland cement (OPC) stabilized soft clay. The unconfined compressive strength of stabilized soft clays at 14, 28, and 56 days was measured to assess their mechanical performance. To analyze the stabilization process, the concentrations of Ca, Si, Al, and Zn in pore water separated from stabilized clay slurries at early ages were measured. The results revealed that GFA was effective to activate GGBS for soft clay stabilization, and the addition of a proper amount of Na2CO3 accelerated the hardening of stabilized clays, led to higher strength at early ages, and reduced the leached heavy metals.