Effect of metakaolin on natural volcanic pozzolan-based geopolymer cement

This work describes the effect of metakaolin on the microstructure and compressive strength of geopolymeric systems based on natural volcanic pozzolans. The effect of the molar ratios of SiO2/Al2O3 and Na2O/Al2O3 and the percentage of metakaolin present in the mixture was studied. The proportion of MK varied between 0 and 30%. A mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as an alkaline activator. The mechanical strength of the geopolymeric pastes and the microstructural properties were evaluated, and techniques such as X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used. The optimum proportion of MK was 20%, incorporated as a replacement of the natural pozzolan. The results obtained in the present study reveal the possibility of obtaining a geopolymeric cementing material with a compressive strength of up to 68 MPa at 28 days of curing at room temperature (25 ± 3 °C).