Abstract
Abstract A coarse mineral with 70% kaolinite and 30% quartz was calcined and chemically activated by alkaline solutions of Na 2 SiO 3 and NaOH. The compressive strength evolution was investigated as a function of the curing temperature at 20 and 80 °C, and the molar ratios of SiO 2 /Al 2 O 3 (2.64–4.04) and Na 2 O/Al 2 O 3 (0.62–1.54). For curing at 20 °C, the best composition was SiO 2 /Al 2 O 3 = 2.96 and NaO/Al 2 O 3 = 0.62, reaching 85 MPa at 28 days. Curing at 80 °C had a positive effect on the strength development only in the first 3 days. X-ray diffraction of the geopolymeric formulations showed the formation of amorphous silicoaluminates of similar nature. The microstructure consisted of unreacted quartz and metakaolinite particles in a matrix of silicoaluminate polymer and condensed silica gel from the unreacted sodium silicate.
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