Geothermal clay-based geopolymer binders: Synthesis and microstructural characterization

Geothermal clay rich in kaolinite was first prepared into geopolymer binders. Preparation conditions of calcination on geothermal clay, Na2SiO3 and NaOH combination in alkaline activator, and water content were studied. Thermal nature of the geothermal clay was characterized by TG-DSC and XRD measurements, which shows characteristics of kaolinite and cristobalite during calcination. Mechanical property, morphology and microstructure of the geothermal clay-based geopolymers were characterized by compressive strength measurements, SEM observation and NMR spectra analysis. With optimal synthesizing parameters, geothermal clay-based geopolymer possessed a compressive strength of 19.5 MPa, as well as a homogeneous geopolymeric gel with high percentages of Q4(2Al) and Q4(1Al). As geothermal clay is supposed to be of intermediate dissolution reactivity in geopolymerization, this synthesis might extend the kinds of raw aluminosilicates in geopolymer formation.